Tree of the Month

A  Feature of History at Home
by Paul W. Meyer, Conservancy Board Member and
Morris Arboretum’s Retired F. Otto Haas Executive Director

Trees are essential to Chestnut Hill’s sense of place. Not only do they beautify our community but they also clean and cool the air, fix co2, while producing life-giving oxygen. Trees are critical in protecting our watershed, insuring a steady and clean supply of water.

Residents of Chestnut Hill are fortunate to have inherited a bounty of large canopy trees as well as smaller flowering trees. But we can’t take this wonderful legacy for granted. We must not only care for our aging trees but also plan and plant for the future urban forest.

Going forward, the Chestnut Hill Conservancy will regularly highlight special trees in our community, both large and small, as well as common and obscure. In doing so, we hope to promote an appreciation of our arbor legacy and foster a culture of stewardship and renewal of this invaluable resource.

APRIL – YELLOW MAGNOLIAS

In recent decades, new hybrid selections of yellow flowering magnolia have been introduced and are now becoming more widely available.  Many of the yellow magnolias are the result of crosses made between the American cucumber tree magnolia, Magnolia acuminata, and the Yulan magnolia, Magnolia denudata. The combination of these two parents has resulted in many cultivars which flower later (late April) than the more common star and saucer magnolias.  They are sometimes fragrant and range from light butter yellow to a golden yellow.  Since they flower later, they are less likely to get hit by a late frost.

These selections are generally destined to become big, tall trees.  The American parent is a canopy tree growing to over 100’ tall.  Its flowers are relatively small compared to other magnolias and it flowers after the foliage emerges.  Though the flowers are somewhat inconspicuous, its genetics enable the yellow pigment important to this breeding line.  Its Chinese cousin can reach 60 feet tall and has large, showy creamy-white flowers, which appear before the leaves.

The cultivar ‘Elizabeth’ was an early hybrid selection introduced in 1978 by the Brooklyn Botanic Garden.  Its pale butter yellow flowers are produced at a very young age.  It is a rapid grower, and it is a good tree for the impatient tree planter.   Three fine maturing trees frame the upper curve on the Morris Arboretum driveway.  It is a Pennsylvania Horticultural Society Gold Medal winner.

‘Butterflies’ is another outstanding selection that is becoming available from nurseries.  It seems to be somewhat smaller in stature and the flowers are a deeper yellow.  Its form tends to be somewhat irregular, differing from the more formal upright, pyramidal form of ‘Elizabeth.’ 

With each passing year, more yellow cultivars of Magnolia are being introduced.  The Morris Arboretum has many in its plant collection and offers a good opportunity to pick your favorite.  The Scott Arboretum at Swarthmore College also has an outstanding collection. 

Arbor Day in Pennsylvania is the last Friday in April.  Celebrate by planting a tree for future generations, in your garden or your neighborhood.  Make a difference… plant a tree.

Photos by Paul W. Meyer (See gallery below for more photos)

MARCH – CORNELIAN CHERRY DOGWOOD

Cornelian Cherry Dogwood – Cornus mas

The cornelian cherry dogwood is among the first trees to flower here in Philadelphia in the late winter or early spring.  The individual yellow flowers are small, but the profusion of flower clusters create a showy display that is a welcome respite from winter.  Unlike its American relative, common flowering dogwood (Cornus florida) which has large colorful bracts, the flower bracts of Cornus mas are small and not conspicuous. This species has a broad native range across Europe and into Asia.   Its Asian form is generally considered a separate species – Cornus officinalis.  Though it is slightly showier, it is relatively rare in cultivation in the US, though fine specimens can be seen at the Morris Arboretum, including one dramatic specimen growing along Hillcrest Avenue. 

The flowers are followed by small fruits which ripen to a bright red color in the autumn. They are tart but edible and rich in vitamins.  In their native lands, fruits are harvested and used for fruit juices and jams.  In both Europe and Asia, clones with larger, sweeter, and more prolific fruits have been selected for orchard cultivation.  Some of these cultivars are becoming available from specialty nurseries in the US.  Birds and other wildlife also benefit from the fruits.

Fruits are also widely used in traditional medicine as a tonic and to treat many ailments including diabetes, obesity, and gastrointestinal disorders.  Scientific studies support the efficacy of some of these treatments, but further clinical trials are needed.

The wood of the cornelian cherry dogwood is very hard and durable.  Traditionally, its wood has been used for bows, spears, wheel spokes and ladder rungs.

The Cornelian Cherry dogwood is a small tree, not usually exceeding 25 feet and often broader than tall.  It can be grown as a single or multi-stemmed specimen.  It is a useful stress-tolerant urban tree, more adaptable to difficult conditions than our native flowering dogwood.     It is generally resistant to insects and diseases.             

Photos by Paul W. Meyer (See gallery below for more photos)

FEBRUARY – SAWARA FALSECYPRESS

Sawara Falsecypress – Chamaecyparis pisifera

The Sawara falsecypress is perhaps the most unknown but common conifers growing widely in Chestnut Hill, Mt. Airy, and the surrounding older northwest suburbs. I believe it is little known because its beauty is subtle, with olive green foliage and somewhat irregular form at maturity. With no showy flowers or fall color, at no time does its beauty jump out and demand attention like a magnolia or dogwood. Hence, it tends to recede into the background.

The genus Chamaecyparis is in the Cypress Family (Cupressaceae), related to bald cypress, junipers, and arborvitae. This species is from central and southern Japan and was first introduced into the U.S. in 1861. By the early 20th century, it was widely available from nurseries in our region. In Japan, it is an immense forest tree, growing to be over 150 feet tall and can live for many hundreds of years. Here in Chestnut Hill, I suspect that landscapers in the early 1900s saw small, handsome, pyramidal trees in the nursery and had no idea that these were truly tall, forest trees. Hence, we today see them growing to 60-70 feet on older properties as foundation plantings and hedges, used the way small clipped yew trees might be planted today. Though not always growing in an ideal location for such a big tree, many are now over a century old. They have survived and thrived and contribute significantly to the sense of place of Chestnut Hill.

In its native land, Sawara falsecypress is a valued forestry species. Its rot resistant, lemon-scented wood used for furniture, construction, boxes, coffins, and musical instruments.

The Sawara falsecypress is remarkably variable. Today, most sawara falsecypress available in nurseries are cultivars, selected for outstanding texture, foliage color and slower growth rate. Common selections include ‘Boulevard’ with silvery blue needle-like foliage, ‘Filifera’ with thread-like weeping branchlets, and a golden threadleaf form – ‘Filifera Aurea’. Perhaps the oldest is C. pisifera ‘Squarosa’. This remarkable form maintains its distinctive juvenile needle lite leaves into maturity. Its needles are silvery blue with a soft texture. These are just a sampling of the scores of cultivars cultivated throughout the world.

Sawara falsecypress is well-adapted to our climate, most moist, well-drained soils and is relatively pest free. It will grow in full sun or light shade.

Look around your neighborhood, especially around properties developed in the early 20th century and try to find one. Then, take time to admire its beautiful, shredding reddish bark and picturesque branch habit. Before long, I think you will be surprised how many fine old specimens of sawara falsecypress you will find growing throughout our community!

Photos by Paul W. Meyer (See gallery below for more photos)

JANUARY – EASTERN WHITE PINE

Eastern white pine is the tallest tree in the eastern North American forest. Many trees more than 150 feet have been recorded and historical accounts note trees exceeding 200 feet. It is a long-lived species, often living more than 200 years, and trees over 450 years old have been observed. Its natural distribution ranges from the southern Appalachian Mountains in Georgia northward into southeastern Canada, and northwest into Ohio, Michigan, Wisconsin, and Minnesota.

Before settlement, extensive forests of enormous white pine were common within its range. Its wood has been highly valued for many purposes including construction, interior woodwork and furniture. Historically, the tall, straight, strong trunk was the favored wood for ship masts. The wood is very strong in relation to its light weight, making it ideal for this use. In 1691, an act of the British Parliament of England declared the tallest and best of the trees were property of the Crown. Because of the white pines’ great value, this declaration led to increasing unrest in New England culminating in the 1772 Pine Tree Riot in New Hampshire. These disputes with the crown over ownership of white pines is often considered a contributing cause of the American revolution.

The old growth white pine forests were heavily cut in the 19th century, until only a few inaccessible stands of virgin pine survived. Today, white pine is widely planted for reforestation and reclamation of mining sites and is still considered a valuable lumber tree.

Here in Chestnut Hill, white pine is an important landscape tree. Once established, it grows rapidly, up to 3 feet a year for the first few decades of its life. After that, growth gradually slows to less than 1 foot a year. When young, eastern white pines have a formal, pyramidal form, but as they mature the crown opens and becomes more irregular. It is common for eastern white pine branches to break in storms, contributing to a picturesque habit. Beautiful mature white pines can be seen throughout our communities, often towering over nearby homes. Notable white pines can be seen in Pastorius Park and the Morris Arboretum.

Because of their eventual size, white pines should be sited with care, allowing them space to grow. They grow best in well drained, acidic soils, and in full sun; in shade, they are less dense and spindly.

White pine is considered an excellent tree for wildlife, providing food, shelter and habitat for birds, foxes, squirrels and small rodents. Mature white pines are a favored nesting tree for bald eagles.

Often, when trees are grown literally by the millions, unusual forms caused by genetic mutations may occur. When these mutants are of special interest to landscapers and gardeners, they can be selected, asexually propagated, and given a cultivated variety (cultivar) name. White pine has many cultivars including ‘Nana’ (slow growing), ‘Fastigiata’ (upright) and ‘Pendula’ (weeping). These can especially be useful in small gardens, where the full height and breadth of a white pine can be overwhelming.

Photos by Paul W. Meyer (See gallery below for more photos)

DECEMBER – WINTERBERRY HOLLY

Winterberry Holly – Ilex verticilla

A heavily fruited winterberry holly is one of the most outstanding plants of the holiday season.  It is beautiful outdoors in the garden and fruited cut branches hold up well as indoor decorations.  Though not technically a tree, it grows to be a large, multi-stemmed shrub reaching 10-15 feet tall.

It is native to eastern North America and is most commonly found growing in moist areas along streams and on the edges of swamps.  Unlike the evergreen American holly, its leaves turn yellow in the autumn and quickly drop, highlighting its bright red fruits borne on dark charcoal colored branches.  As the holiday season approaches, bundles of fruited branches can be found on sale in garden centers and markets.

In cultivation, winterberry holly adapts well to most moderately moist, acidic soils.  Though it tolerates shade, it fruits most heavily in sunny locations.  As plants mature, they sucker from the ground, eventually forming a dense thicket.  This characteristic, along with its prolific root system, makes it useful in stabilizing stream banks and controlling erosion.

Hollies are dioecious, bearing male and female flowers on separate plants.  Since this shrub is grown primarily for its fruit, most gardeners prefer female clones, selected for their especially prolific fruit set.  But, of course, a male must be in the neighborhood to get pollination and consequently good fruiting.

In recent decades, many clones of winterberry holly and its hybrids have been selected, with a variety of fruit colors including reds, oranges and yellows.   Clones can flower at slightly different times in the spring, so it is important that the male match the flowering times of the female.  To facilitate this match-making, male clones are sold paired with particular female clones.  This chart can help with pairing:  https://www.skh.com/wp-content/uploads/2011/06/Winterberry-pollination.pdf

‘Winter Red’ is one of my favorite cultivars.  Its fruits historically have lasted long into the winter, providing late winter food for birds when it is otherwise scarce.  But in recent year, birds have stripped my ‘Winter Red’ winterberry hollies much earlier, sometimes even before the end of the year.  To be safe, if you want the fruited branches for indoor holiday decorations, harvest early and store the cut stems in a cool protected location until ready to use.

Good pollinators for ’Winter Red’ include ‘Southern Gentleman’ and ‘Apollo’.  One mature male will provide pollinators with enough pollen to fertilize many flowering females throughout the neighborhood. For smaller gardens, choose one of the slower growing, compact selections.  ‘Red Sprite’ and ‘Shaver’ are two widely grown dwarf female cultivars.  ‘Jim Dandy’ is a good dwarf male pollinator.

In planning any garden, it is important to include plants that will provide dynamic interest every month throughout the year.  Winterberry Hollies will dramatically fill the early winter gap when little else is happening in the garden.

Photos by Paul W. Meyer (See gallery below for more photos)

NOVEMBER – PERSIAN PARROTIA

Parrotia persica – Persian Parrotia

The Persian Parrotia is a tough, adaptable tree, well suited to the rigors of urban life in Philadelphia.  As its name implies, it grows natively in Iran but also in nearby Azerbaijan, in the mid-elevations of mountains along the Caspian Sea.   It was first grown in the U.S. in 1881 at the Harvard Botanic Garden and soon after at the Arnold Arboretum of Harvard University, but even today, it is relatively rare in cultivation outside of botanic gardens and arboreta.

Parrotia is a member of the witch hazel family.  In addition to witch hazel, its well-known close relatives include sweet gum and Fothergilla.  It has small flowers which appear here in early March.  The flowers lack petals but have a dense cluster of red stamens that are beautiful when viewed closely.   in flower, from a distance the entire tree has a maroon-red haze.  As Parrotias age, they develop mottled, exfoliating bark that is attractive year-round.  Parrotias grab the landscape limelight in late October when the foliage takes on shades of deep burgundy.  As the autumn progresses to mid-November, the foliage takes on brilliant shades of scarlet, mixed with orange and yellow.  At the Morris Arboretum the most brilliant autumn display is usually between the 10^th and the 15^th of November. 

Among the Parrotias at the Morris Arboretum are 8 plants that were received as seed from Iran via the Royal Botanic Garden, Edinburgh.  These seedlings represent new wild-collected germplasm for a species that has been genetically underrepresented in this country.  One of the most outstanding trees from this accession is growing in a prominent site on Bloomfield Farm along Northwestern Avenue near the main entrance.  This tree consistently has outstanding fall color.

In recent years, a few plantings of Parrotia on Philadelphia streets have demonstrated the species’ urban adaptability.  Once established Parrotia is highly heat and drought tolerant and remarkably free from pests.  As we consider the impact of climate change on our urban trees, Parrotia is a tree that is likely to continue to thrive in warmer, drier conditions and is likely to be among the urban survivors.  Also, its wood is strong and hard and resists breakage, an important quality for urban trees.  One is growing in a tree planting pit along Germantown Avenue and have been doing well there since 2016. 

As we work to diversify our urban street tree plantings, Parrotia is a species that is an excellent candidate for planting more widely. 

Photos by Paul W. Meyer (See gallery below for more photos)

OCTOBER – BLACK GUM, TUPELO

Nyssa sylvatica – Black Gum, Tupelo

For a native tree that is widely distributed across most of eastern North America, black gum (Nyssa sylvatica) is surprisingly little known in our landscapes.  Perhaps it is because its entire, dark green, oval leaves are relatively nondescript.  Or maybe it is because it is usually widely scattered in woodlands, seldom in pure stands.  Also, since it is relatively slow-growing and difficult to transplant, many landscapers elect to plant another tree that might provide more instant gratification.  Though not widely planted here in its native homeland, it is revered and celebrated in gardens and arboreta abroad, especially in the U.K. and Europe.

Black gum is indeed an exceptional shade tree that should be more widely planted here in its homeland.  In the Wissahickon Valley it can be found growing naturally on the streamside as well as on the dry, higher slopes. It is a tall canopy tree and its foliage in the forest is often hard to observe.  Its flowers are small, and not likely to attract attention, unless you are a honeybee.  Honey from tupelo flowers (especially the more southern species Nyssa ogeche) was made famous by the 1971 Van Morrison hit song and is sometimes called the “queen of honey”.  Flowers on individual trees tend to be largely male or female (polygamo-dioecious).  Female flowers successfully pollenated produce small blue-black fruits in the autumn that are relished by birds and other wildlife.

Black gum’s outstanding moment of fame comes in late October and early November when the shiny, dark green leaves take on shades of yellow, orange and especially, vivid crimson.  The iconic grove of black gums at the Morris Arboretum, growing on the slope above the rose garden, creates a dramatic show year after year.    

Increasingly, black gum trees grown in large containers are being sold, making transplanting easier and more reliably successful.  Also, in recent decades, cultivars have become available that are selected for their upright form, resistance to leaf spot diseases and most important, exceptional fall color.  Two popular cultivars that are becoming available are ‘Green Gable’ and ‘Wildfire’.  

Planting a black gum is an investment for the next generation.  Though slow growing, a black gum can live for hundreds of years and achieve heights of over 100 feet.  It is well adapted to most soil conditions, but not high pH.  I have seen evidence in recent years that black gum can tolerate stressful streetside conditions, including several trees growing here in Chestnut Hill along Germantown Avenue.  Last spring two black gums were planted in the small park just below Mermaid Inn and a small specimen of Nyssa sylvatica ‘Wildfire’ will soon be planted in Pastorius Park near Lincoln Drive by the Friends of Pastorius Park.

Photos by Paul W. Meyer (See gallery below for more photos)

SEPTEMBER – RIVER BIRCH

River Birch – Betula nigra

As the common name suggest, river birch is a riparian species, well adapted to moist streamside soil conditions and occasional flooding.  It is distributed widely across the eastern U.S., from Texas and Florida northward through the upper Midwest and New England.  In Chestnut Hill, it is widely cultivated and can be found growing naturally scattered along the banks of the Wissahickon Creek. 

Unlike the more northerly birch species with pure white bark, it is tolerant of summer heat and thrives in the south.  Though it lacks the dramatic smooth, white bark of paper birch, its flakey bark is attractive in a more subtle way.  The color and texture of the bark varies from one individual to the next, ranging from a deep cinnamon color to a pale tan.  Cultivars have been selected for their light-colored, heavily flaking bark.  The most widely planted cultivar is ‘Heritage’.  Trees found in the wild are more likely to have darker bark that is less strongly exfoliating.

Here in southeast Pennsylvania, river birch is the preferred choice for a long-lived birch, since it is well adapted to our hot summers and resistant to the bronze birch borer which can devastate paper birches and the European white bark birch.  River birch tends to drop its leaves early in a drought, but usually no lasting harm is done.

River birch can be grown with a single stem or with multiple stems.  Multi-stem specimens highlight its beautiful bark character.  It is a relatively fast-growing tree and can exceed a height of 70 feet.   As it matures, branches can be somewhat brittle, so it is best to plant a safe distance from structures.

Photos by Paul W. Meyer (See gallery below for more photos)

AUGUST – GREEN ASH

Green Ash – Fraxinus pennsylvanica

Green Ash is a native tree, widely distributed across eastern North America.  In its natural setting, it occurs most frequently along streams and in low, moist areas.  The wood of ash trees is notably strong and relatively light.  It is the preferred wood for baseball bats, and it is also often used for tool handles.  Until recently, it was widely planted in some cities as a street tree. 

That strategy changed dramatically with the arrival of the emerald ash borer, a destructive insect which arrived from Asia.  First documented in Southeastern Michigan in 2002, it is believed that the borers came hidden in the wood of shipping crates from China.   The beautiful emerald-green female adults lay their eggs in bark crevices of the ash trees.  When the eggs hatch, the larvae bore into the tree and feed on the inner bark and phloem, girdling the tree, thereby causing extensive canopy dieback and eventual death.  When the emerald ash borer moves into an area, it is nearly 100% fatal to both green ash and its close relative the white ash (Fraxinus americana).  Today, dead and dying ash trees are a common site in Chestnut Hill.  Once infested, the tree should be quickly removed before it becomes brittle and dangerous.

Trees that are still healthy can be protected with systemic insecticides.  These insecticides can be applied as soil drenches, trunk injections or as sprays on the bark of the lower trunk.  They cannot reverse damage that is already done, so it is important to begin treatment early, ideally before symptoms of crown thinning and branch dieback begin.  Detailed information on the emerald ash borer and its treatments can be found here:  www.emeraldashborer.info

 For now, of course, ash should not be planted.  Looking to the future, US Department of Agriculture is conducting research on several species of stingless wasps that attack the emerald ash borer larvae and eggs.  They have been released in 25 states and early results are encouraging. 

Also, some Asian species of ash have shown natural resistance to the emerald ash borer.  Many of these have been collected by the Morris Arboretum in collaboration with other arboreta in the US, Canada and China, and are growing successfully in their collections.  These may be used in breeding or gene editing to produce resistant hybrids.  These are potentially long-term solutions, but meanwhile many more millions of ash trees will die.

The demise of the ash is another cautionary example of the importance of maintaining high levels of diversity in our urban tree plantings.  As with the American elm, American chestnut, and the Canada hemlock, virulent insects and diseases have devastated our populations of these susceptible species.  By maintaining maximum species diversity, we can hedge our bets and help ameliorate the impact of these and future epidemics in our community’s urban forest.

Photos by Paul W. Meyer (See gallery below for more photos)

JULY – HONEYLOCUST

Thornless Honeylocust
Gleditsia triacanthos var. inermis

The thornless honeylocust is one of the most widely planted street trees in Philadelphia and with good reason.  It has good upright form, and a light, open crown. Its doubly compound leaves with small leaflets give the tree an airy feel, allowing dappled light to pass through the crown.  It is also tolerant of heat, drought and deicing salts.   In short, is an ideal urban street tree, often seen thriving in inhospitable streetside tree pits.  In some areas of the city, it is so widely planted that its planting should be limited to insure adequate diversity in the urban forest.

Honeylocust is a native tree, often found growing on floodplains.  It occurs naturally from Pennsylvania west to Nebraska and south to the Gulf Coast.  It is dioecious, bearing male and female flowers on separate plants.  Female plants bear long, twisted seed pods that drop throughout the fall and winter, creating potential tripping hazards when they fall on sidewalks.  Thus, male clones are preferred for landscape plantings.  In the wild, honeylocusts bear long, sharp branched thorns that are hazardous in landscape plantings. 

Fortunately, many clones that are both male (fruitless) and thornless have been selected.  These clones also have been selected for uniform canopies, ranging from narrow upright to broad spreading forms.  Some commonly planted clones are ‘Skyline’ (upright, central leader), ‘Halka’ (rounder, more spreading form) and ‘Shademaster’ (vase-shaped, ascending canopy).  These are just a few of the many cultivated clones available from nurseries.

The pods of honeylocust are sweet and devoured by wild and domestic animals including cattle, pigs, deer, rabbits and squirrels.  Honeylocust wood is strong, durable and rot resistant, formerly used for railroad ties, fence posts, and structural beams.  It was the favored tree for bow making by the Cherokee tribe of Tennessee.

Photos by Paul W. Meyer (See gallery below for more photos)

JUNE – KOREAN STEWARTIA

Korean Stewartia – Stewartia koreana

I am often asked what is one tree I would I choose for a small garden.  It would be a tree that has relatively small stature, beautiful flowers, excellent fall color and winter interest.  If one can have only one tree, it should be attractive every season of the year.

A number of trees come to mind, but a favorite is the Korean stewartia.  It has outstanding white flowers for 2-3 weeks in June, orange to red fall color, and beautiful smooth, mottled bark that is attractive year-round.  Its native range is limited to South Korea, but it has a close relative, Stewartia pseudocamellia, from Japan.  Some botanist have argued that these are the same species, but recent molecular work has confirmed that they are genetically distinct species, though closely related.

Though Korean stewartia has been grown in the US since 1917, it is still relatively rare in landscapes outside of Arboreta, where is considered a must-have specimen.  It is generally available from specialty nurseries or garden centers that cater to connoisseurs.   A few cultivars have been selected for particularly showy flowers, but tese are not widely available.

Korean stewartia is easy to grow in soils that are moist but not too wet and is generally pest resistant.  It is not highly drought tolerant, especially when newly planted.  I would not normally recommend Stewartias for stressful street-side conditions, but a prominent plant on Highland Avenue in front of BMT offices is doing well.  Stewartia is relatively slow growing.  I have seen Stewartia in South Korea up to 60’ tall, but here in cultivation, it is typically under 35’. 

Photos by Paul W. Meyer (See gallery below for more photos)

MAY – TULIPTREE

Tuliptree – Liriodendron tulipifera

The tuliptree is among the tallest and most majestic native trees of Pennsylvania.  The trunk is usually very straight and clear of branches high up into the tree.  For that reason, it is valued not only for its landscape beauty but also for the lumber it yields.  The wood tends to be straight grained and useful for construction grade lumber and plywood.    It is also used for cabinets, veneer, furniture and pulp.  Because the wood is light, it was used by Native Americans for dugout canoes.  In the lumber industry it is referred to as yellow poplar, though it is not a poplar, but rather a member of the Magnolia Family.

It is widely distributed across eastern North America.  In the southeastern part of its range it can grow to monumental heights, reaching over 200 feet tall with a diameter of 10 feet or more.  Closer to home, fine specimens of tuliptree occur throughout with Wissahickon Valley.  Particularly outstanding groves can be easily seen from Forbidden Drive, a short distance downstream from Valley Green Inn.  Here and throughout its range, the largest specimens tend to grow best in the lower valleys where the soil is deeper and richer. 

In the managed landscape, tuliptree is a fast growing, upright tree, but it can sometimes be brittle.  Thus, it is best suited to larger properties and should not planted too close to structures.  It is largely resistant to serious pests, though aphids and Magnolia scale are sometimes a problem.  As in its natural habitat, it grows best in deep, rich, moist but well-drained soils.  It is not a good choice for stressful street side conditions where soil volume is limited.

Our American tuliptree is admired and grown throughout the temperate world.  It is valued for its unusual leaves, its dramatic orange yellow flowers which appear in early May, and its clear, luminous yellow autumn color.   It is an outstanding tree worth growing in natural areas, forest restorations and cultivated landscapes where it has plenty of space for both its roots and its expansive canopy.

Photos by Paul W. Meyer (See gallery below for more photos)

APRIL – YOSHINO CHERRY

Yoshino Cherry – Prunus x yedoensis

 Flowering cherries, sakura, have been an important part of Japanese culture for centuries.  They symbolize the coming of spring and the renewal of life.  In Japan each year, when they reach their peak of bloom, work life pauses, and people flock to the parks to eat and drink under the strikingly beautiful cherries.

There are many species and many hundreds of cultivated varieties of flowering cherries.   The Yoshino cherry is considered to be among the most beautiful and floriferous.  Its flowers open pale pink and quickly fade to pure white.  In Japan the ephemeral nature of the flowers are considered to be part of its magic.  The origin of Yoshino cherry is not known, but modern gene sequencing has confirmed that it is a hybrid, probably of natural origin.  For centuries, this hybrid has been cherished and widely planted in Tokyo and other Japanese cities.

In the 19^th century, the Japanese flowering cherries were admired by western visitors and introduced slowly to the western world.  In 1912, over 3,000 flowering cherries were sent as a gift of friendship to the people of the United States from the people of Japan.   Though this gift contained a number of varieties, and Yoshino comprised well over half of the shipment.  These were mainly planted around the Washington D.C. tidal basin.  Today, Yoshino cherry continues to predominate the tidal basin because of its beauty, vigor and adaptability.

Closer to home, in 1926, 1600 cherry trees were gifted from Japan to Philadelphia in 1926 in honor of the American Sesquicentennial.  In 1933, Japanese residents of Philadelphia donated 500 flowering cherries to be planted along the Schuylkill River near Kelly Drive.  More recently between 1998 and 2007,  the Japan American Society of Greater Philadelphia planted 1000 cherries, including many Yoshino cherries, in Fairmount Park, while sponsoring intercultural cherry blossom festivals throughout the city, including at the Morris Arboretum.

Yoshino cherry is easy to grow and relatively pest free.  It transplants readily and grows quickly.  It is precocious, flowering heavily from a young age.  Yoshino cherry grows to 50-60 feet and is usually broader than tall at maturity.  Flowering cherries as a group are not long lived, but Yoshino sometimes lives 100 years or more.  At the Morris Arboretum we have had success in rejuvenating old, declining trees with a very hard pruning, greatly extending their life span.

The weeping form of Yoshino cherry is among the most graceful of the many weeping cherries cultivars.  A fine example of this rare form can be seen at the Morris Arboretum.

Photos by Paul W. Meyer (See gallery below for more photos)

MARCH – SHADBUSH, SERVICEBERRY

Amelanchier arborea, Amelanchier laevis, and the hybrid, Amelanchier x grandiflora
Shadbush, also known as serviceberry, will soon push forth its delicate white flowers.  These members of the rose family are native Pennsylvania trees, typically found growing on the woodland edge or woodland understory.  The two arboreal species occur throughout Pennsylvania and are among the first trees with showy flowers to bloom in early to mid-April.  The delicate flowers stand out because most of their forest neighbors are still dormant. 

Its common name, shadbush, suggests that it blooms at the time the migratory shad are running in the coastal Atlantic rivers.  Also, legend has it that the name serviceberry was given because it blooms at the time the early itinerant ministers made their call for the first services of the spring.  The wood of mature Amelanchier is quite dense and was traditionally used for tool handles because of its durability and strength.

Today, shadbush is very useful in urban and suburban cultivated landscapes.  It is often multi-stemmed and its sculptural silhouette is very attractive against a wall or building.  Its bark is smooth, silvery-gray in color with subtle striations.   Flowers are followed by fruits, which turn from green to red and eventually dark blue as they ripen in June.  The fruits are edible and provide a feast for birds, who quickly devour them.   It is a relatively small tree, seldom growing beyond 40’ and is appropriate for planting near buildings or in confined spaces.  In forest restorations it is best planted in canopy gaps or on the forest edge. 

Shadbush leaves can be infected with a variety of fungal problems, causing early leaf drop.  Usually, this does little lasting harm, but detracts from late summer and fall attractiveness, particularly in garden settings.  Therefore, when planting shadbush in the garden, select cultivars that have been chosen for their disease resistance.   This will help insure the leaves will persist until autumn when they typically turn to brilliant shades of red and orange. 

With its flowers, fruit, fall color and attractive bark, shadbush is truly a plant with four seasons of interest.  Some common improved cultivars to consider planting are ‘Standing Ovation’, ‘Autumn Brilliance’,   and ‘Princess Diana’.       

FEBRUARY – WINTER BLOOMING WITCH HAZELS

As winter drags on into February and March, nothing lifts our spirits and kindles the hope of spring like the winter-blooming witch hazels that sometimes starts blooming as early as January.   These are large shrubs or small, usually multi-stemmed trees, occasionally growing up to over 20 feet in height.  They are primarily derived from three species – Chinese witch hazel (Hamamelis mollis), Ozark witch hazel (H. vernalis) and Japanese witch hazel (H. japonica).

I first encountered winter blooming witch hazel while working in the famed Hillier Arboretum in southern England.  After traveling to Germany for the Christmas holiday season, I returned to the Arboretum in early January, 1974  and was delighted to discover Hamamelis x intermedia ‘Pallida’ in full flower, seeming to glow in the dim English winter light.  This particular one grabbed my attention from afar, but I soon discovered a number of others growing nearby.  Thus began my annual winter fascination with these surprising winter blooming witch hazels.

Until recent decades, winter blooming witch hazels were relatively unknown outside of botanic gardens and connoisseur’s gardens, and little work had been done in selecting superior flowering forms.  In 1963, the Arnold Arboretum of Harvard University introduced one of the early hybrid cultivars, ‘Arnold Promise’.    The original plant was grown from seed taken from a Chinese witch hazel in the collection where the Japanese species was growing nearby.  As the seedling matured, its profuse flowering attracted attention, and its characteristics were determined to be intermediate between the Chinese and Japanese species.

Working independently in Belgium, Jelena de Belder of Kalmthout Arboretum was smitten with witch hazels.  Building upon an existing collection, she raised and evaluated thousands of seedlings, ultimately introducing many cultivars selected for heavy flowering, scent and various shades of yellow, orange and red.  Some of her most famous introductions include ‘Jelena’, ‘Diane’, ‘Limelight’, Primavera’ and ‘Ruby Glow’.

In recent decades, many other enthusiasts have continued to hybridize and select new cultivars.  Today there are well over one hundred cultivars, and that number continues to grow.  Many of these can be seen at the Morris Arboretum but most are not easily available commercially.  A number of my favorites are pictured here to demonstrate the range of variation.

These witch hazels are fully winter hardy and easy to grow in full sun or light shade.  They grow best in moist but well-drained soils.  Functionally, it is best to site plants where they can be easily seen and enjoyed from the indoors on a cold winters day.

The flower petals are coiled in the buds like watch springs, and early in their flowering period, have the ability to curl back up when the colder weather hits.  The petals themselves are remarkably cold-hardy, though they tend to be more easily damaged toward the end of their flowering period.  Branches can be cut and brought indoors any time after the New Year, and they will quickly open and bring the color and fragrance of spring into your home.

Our local garden centers may carry some selections.  Joe Ascenzi of Laurel Hill Gardens will have a number of witch hazels in the spring.  Colibraro Nursery, a local wholesaler is a source for your landscaper or retail nursery.  Also, an outstanding collection is available by mail order from www.gosslerfarms.com.  Plan to plant this spring for your enjoyment next winter.

JANUARY – CANADIAN or EASTERN HEMLOCK – Tsuga canadensis

The Canadian or eastern hemlock is among the most beautiful of our native conifers.  It has a native range stretching from eastern Canada south to the mountains of northern Georgia and Alabama.  At its best, it is a long-lived, massive forest tree reaching heights of over 150 feet.  Trees in the Smokey Mountains have been documented to be well over 500 years old.

Here in Pennsylvania, Canadian hemlock does not grow quite so large but is widely distributed throughout the state.  In northern parts, nearly pure stands of majestic hemlock trees still persist, though here in the southeast, hemlocks are more scattered, mainly on the north slopes of stream valleys, like the Wissahickon.   It is also widely cultivated in our landscapes, often to provide screening for windbreaks and privacy.  It is highly shade tolerant compared with many other evergreen conifers and grows well among and under deciduous trees.  Since 1931, Canadian hemlock has been the official state tree of Pennsylvania.

The bark of Canadian hemlock is rich in tannins.  Native Americans used the boiled bark to treat wounds and stop bleeding.  Hemlock bark was an important tannin source for the leather industry.

In recent decades, Canadian hemlock has been plagued by an insect, the hemlock wooly adelgid.  This sucking insect looks like small, cottony masses on the underside of the needles.  This pest is common in the Wissahickon Valley forest as well as in our landscapes, causing thinning of the tree’s crown and often eventual death.

Many notable, healthy, mature Canadian hemlocks are growing in Pastorius Park.  Through the efforts of the Friends of Pastorius Park, these trees have been treated regularly to control the wooly adelgid, as well as elongate hemlock scale, another troublesome insect pest.  Healthy hemlocks like these in the park are rarely seen today and they demonstrate the lush, delicate beauty for which Canadian hemlock is admired.

In the late 1980s Morris Arboretum staff observed that a rare Chinese Hemlock (Tsuga chinensis) growing in its collection showed resistance to the wooly adelgid.  A review of other specimens of Chinese hemlock growing in the region backed this up.  Since the 1990s The Morris Arboretum has been a member of an international team (The North American – China Plant Exploration Consortium) collecting and evaluating Chinese hemlock from many parts of its natural range in China.  These plants are now maturing and showing great resistance to the wooly adelgid.  In 2006 the Morris Arboretum donated young plants of Chinese Hemlock to Pastorius Park, to be planted in memory of Olivia Skye Eble-Schrader. These trees have thrived and are now over 20’ tall.  They can be seen growing northeast of the pond on the edge of the woods.

Many compact, slow growing cultivars of Canadian hemlock have been selected and asexually propagated over the years.  One of the most dramatic of these is the Weeping Canadian hemlock, (Tsuga canadensis ‘Sargenti’ or ‘Pendula’)   It was found in upstate New York as a natural variant in the 1850s and was first propagated in the 1860s.   It was first shown publicly in Philadelphia at the Centennial Exposition in Fairmount Park.  Two of these trees remain today.  Also, two fine weeping specimens grow at the Morris Arboretum – one near the Swan Pond and the other on the edge of the parking lot near Meadowbrook Avenue.  The Swan Pond tree, documented on a 1909 map, is well over 100 years old.

In spite of the challenges, Canadian hemlocks continues to be planted, but regular treatment is required to keep them healthy.  Chinese hemlock is more reliable but not yet widely available commercially.  Resistant hybrids, developed at the US National Arboretum, are also coming along.  Research is underway evaluating the use of a beetle that preys on the wooly adelgid.  It is hoped that in time, research on many fronts will pay off and Canadian hemlocks will again thrive in the wild as well as in our communities.

DECEMBER – NORWAY SPRUCE – Picea abies

Norway spruce is a very tall, evergreen tree.  This conifer is widely distributed in the wild, native to Scandinavia, as well as central Europe and much of Russia.  It was introduced into cultivation in Britain around 1500 and to the US in the 19^th century.  It was listed in Chestnut Hill’s famous Andorra Nursery 1895 catalogue, under the botanic name of Abies (fir)  excelsa.  It is described as “a valuable tree either as a single specimen or for a grouping, and it also makes a fine evergreen hedge.” Plants were offered at 25, 50, and 75 cents and $1.00 each.  ($1.00 in 1895 is equivalent to $31.00 today – still a bargain.)  Andorra Nursery was probably the origin of the many fine, old trees still growing in Chestnut Hill.  Some of these monarchs exceed 100 feet in height.  Occasionally, a line of closely planted trees suggest it was once a hedge which outgrew their bounds.

Today, Norway continues to be the most common spruce planted in the Philadelphia region.  It is fast growing, pyramidal when young, developing a more open habit with graceful drooping branchlets as it matures.  It is relatively resistant to insects and diseases.  This species is highly variable and many cultivated varieties have been selected and asexually reproduced.  .  Many are slower growing and more compact than the species, while some have a weeping or very narrow, upright habit.  The Hillier Manual of Trees and Shrubs lists over 40 different cultivars, though only a fraction of these are commonly grown.   These compact cultivars are more useful in small landscapes than the massive straight species.

In Europe, Norway spruce is an important forestry tree.  Its wood is widely used in construction, furniture, pulp and musical instruments. It is also grown as a Christmas tree in many regions.  Interestingly, the young green shoots were used to flavor spruce beer (both alcoholic and non-alcoholic).  The needles are rich in vitamin C and thus, this beer helped prevent scurvy.  In recent years, craft brewers have revived these old spruce recipes.  Locally, Yards makes a spruce ale based on Ben Franklin’s original recipe.

As an evergreen, Norway spruce is a welcomed sight in the winter landscape, while providing cover for birds and other wildlife.  The cones are the largest of the spruces, and they fall to the ground intact when ripe.  The seeds provide food for many birds and small mammals.   Fortunately for us, Norway spruce is not a preferred food for whitetail deer, though I have learned not to say that any plant is deer-proof.

The Norway spruce is an important element of our cultural and historic landscapes and continues to be well worth planting where space allows. 

NOVEMBER – AMERICAN HOLLY – Ilex opaca

American holly is one of the relatively few broad-leaf, evergreen trees that grow in our region.  As such, it gives welcome green relief to the gray winter landscape while providing food and shelter to overwintering birds and other wildlife.  Its natural range includes coastal areas from Massachusetts to Texas.  In Pennsylvania native stands are rare, occurring primarily in the lower Susquehanna River Valley.  It can be found in the understory of the Wissahickon Valley, but these plants are likely naturalized from nearby landscape plantings.

American holly is quite slow growing, and in landscapes it is often treated as a shrub.  But when allowed to grow into its natural arboreal form, it can reach well over 60 feet in height.  It withstands shearing and can be planted as a clipped hedge.

American holly is dioecious, with male and female flowers on separate plants.   Hollies are insect pollinated, often by honey bees, so one male in the neighborhood can provide pollen for many females.  Many female clones have been selected, for their more prolific fruit set and often, for dark green foliage.  Some of my favorite clones are ‘Old Heavy Berry’, ‘Satyr Hill’, and Jersey Princess’.   Also, several clones have also been selected for their unusual yellow berries.  A very fine collection of hollies, including many clones of American holly are growing at the Morris Arboretum.  Go to the Arboretum for a winter walk and select your favorite.

Usually birds will not eat the fruits until late winter or early spring.  By then the fruits are beginning to ferment on the trees.  Many years I have observed flocks of raucous robins on a drunken feeding frenzy.  I cannot explain it, but this year in our garden, the birds are already stripping the trees of fruit and not leaving any for late winter, when food is scarcer.

As we enter the dark days of winter, branches of well-fruited holly can be cut and brought indoors as natural decorations.  This tradition dates back to Druid and Roman traditions, who used the closely-related English holly. During the feast of Saturnalia, holly branches were offered to the god Saturn.  Druids thought holly to have magical powers, which brought good luck.   Christians picked up on these seasonal traditions and began associating holly with Christmas celebrations, which are celebrated at the same time of the year.  Of course, the fact that holly is usually looking its best in December, makes it a perfect non-denominational home decoration for the winter season.

OCTOBER – GINKGO BILOBA

Ancient Living Fossil Thrives in Chestnut Hill

Ginkgo biloba, one of our community’s most common and easily recognizable trees, predates mankind on earth by nearly 200 million years. In fact, it was widely distributed on earth during the time of dinosaurs. Amazingly, ginkgo has adapted and persisted, little changed from its ancient ancestors through the eons of time.

This adaptability continues to serve the species well. Ginkgo is highly resistant to urban stress factors including heat, drought, deicing salts and poor soils. It is also resistant to most insects and diseases. For these reasons it is widely planted as a street tree throughout Philadelphia. So when street trees were being selected for Germantown Avenue in the 1960s, Ginkgo was a good choice.

Ginkgo is dioecious, with male and female reproductive organs are borne on separate trees. Ginkgo is a gymnosperm. Its seeds are borne naked, not protected by an ovary. It is most closely related to conifers and cycads, rather than flowering plants. Females, when fertilized by a nearby male, can produce bountiful crop of seeds.  Though the seeds are nutritious and tasty, they are surrounded by a fleshy seed coat that has a rancid smell as it falls to the ground, rotting in autumn. Therefore, to save shoppers and shop keepers this nasty inconvenience, usually male clones are planted. Unfortunately, in Chestnut Hill some unwanted female ginkgoes slipped into the mix, causing quite a controversy before the maturing females were removed in 1980.

In many Asian cultures, the ginkgo seeds are highly valued for food and medicine, and they are quickly gathered when they fall and before they begin to smell. Here in Philadelphia, some Chinese restaurants have dishes with the ginkgo seeds and they send collectors out to gather the seeds off the sidewalks.

Though ginkgo was once distributed on every continent, over time its distribution became much more restricted. It is believed that during recent ice ages, ginkgo neared extinction and was preserved only in a few protected valleys in southern China. For at least 1.000 years, ginkgo, with its unique, attractive leaf and edible seed, reputedly of medicinal value, attracted the attention of religious monks, who cultivated these trees around their temples. In time, ginkgo took on religious significance.  Today, ancient ginkgo trees can still be found in association with Buddhist and Taoist temples and it is difficult in some instance to differentiate ancient cultivated trees from relic wild trees. I have had the pleasure of visiting some of these ancient trees in China, Korea and Japan (see photos in the gallery below).

Ginkgo was first brought back to the western world in the later part of the 18^th century. An old ginkgo still stands in the Royal Botanic Garden, Kew, in London. This tree was planted in 1762. A few decades later, here in Philadelphia, William Hamilton received seed of ginkgo. One plant was shared with William Bartram, who planted his in Bartrams’ Garden. Though the Hamilton trees have been lost, the Bartram specimen still stands proudly, having survived periods of industrialization and pollution.

Here in Chestnut Hill, ginkgoes are most striking in late autumn when the trees take on a brilliant yellow autumn color. But this show is ephemeral, and often, especially if there is a frost, the leaves literally fall overnight, creating an equally striking blanket of gold. Typically they reach their peak of fall color in the last days of October or the first half of November.

In this age of climate change and with the onslaught of new insects and diseases, urban foresters are searching for trees that will persist in our cities for many decades.  Ginkgo continues to be one such urban stalwart. Though it has proven itself here in Chestnut Hill and throughout Philadelphia, we need to be careful not to overplant it and systematically maintain great diversity in our urban tree plantings. Though it truly has survived the test of time, we should not put too many eggs in one basket.  We don’t know what the future might bring, but we hope ginkgo will continue its unparalleled record of survival.

SEPTEMBER – BUR OAK: Quercus macrocarpa

AUGUST – FRANKLINTREE: A Botanical and Historical Treasure

JULY – LONDON PLANETREE

JUNE – AMERICAN CHESTNUT

MAY – COMMON FLOWERING DOGWOOD and EASTERN REDBUD

APRIL – YULAN MAGNOLIA

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Yellow Magnolias

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Cornelian Cherry Dogwood – Cornus mas

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Sawara falsecypress – Chamaecyparis pisifera

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Eastern White Pine

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Winterberry Holly

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Persian Parrotia

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Black Gum, Tupelo

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River Birch

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Green Ash

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Honeylocust

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Korean Stewartia

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Tuliptree

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Yoshino Cherry

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Shadbush, Serviceberry

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Winter Blooming Witch Hazels

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Canadian or Eastern Hemlock

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Norway Spruce

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American Holly

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Ginkgo Biloba

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Bur Oak

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Franklintree

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London Planetree

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American Chestnut

Here is another historic photo of an American Chestnut growing at the Morris Arboretum in the English Park, near the site where the Step Fountain is now located.  The curved roof line of the Fernery can be seen on the left through the branches.  Courtesy of the Morris Arboretum Archives.

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