The Thielke Arboretum in Glen Rock

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            Trees at the Arboretum

An Arboretum is, literally, a "Garden of Trees"


The Thielke Arboretum in Glen Rock has over 170 specimens of trees and shrubs. These are extensively documented, and well marked. This list changes as specimens are added, and in some cases lost. Some of the more interesting trees, shrubs, and collections are noted below.


 

Constitution Walk 

Consitution Walk  has a significant  place in the history of the Glen Rock Arboretum.  In 1987,  members of the Glen Rock Garden Club arboretum  committee wrote to the 13 original states  of the United States of America and  requested a specimen of their state tree. These trees are planted in the arboretum area along Doremus Avenue.


The trees are listed below. The state tree of South Carolina, the Palmetto, will not survive in our climate zone and a Sourwood tree has been planted in it’s place.  As with every ‘growing’ collection,  some trees may need to be  replaced or moved elsewhere due to site and growing requirements.


Children enjoy finding the trees and reading the identifying signs

(and they get a history lesson  as well!).



 State

Tree 

Scientific Name

 Connecticut

White Oak 

Quercus alba 

 Delaware

American Holly

Ilex opaca

 Georgia

Magnolia 

Magnolia virginiana

(in Magnolia Circle)

 Massachusetts

American Elm

Ulmus americana

 Maryland

White Oak

Quercus alba

 New Hampshire

White Birch

Betula papyrifera

(to be replaced - no longer survives in our zone due to climate change)

 New Jersey

Red Oak

Quercus rubra

New York

Sugar Maple

Acer saccharum

 North Carolina

Flowering Dogwood

Cornus florida

Pennsylvania

Eastern Hemlock

Tsuga canadensis

(near Arboretum sign)

Rhode Island

Red Maple

Acer rubrum

South Carolina

Sourwood

Oxydendrum arboreum

(East of pond, near road)

Virginia

Flowering Dogwood

Cornus florida 



Some of our favorites


common persimmon—Diospyros virginiana

Our native persimmon is recognizable by its thick dark bark that appears as distinctive square blocks. Pale orange round 1-1 ½ " long fruit may be found on the ground in October. They are extremely bitter until after frost. Persimmons prefer full sun but will grow well in many places.


sugar maple--Acer saccharum, Norway maple—, A. platanoides

These two trees are often confused. Here, on opposite sides of the path, they may be compared. Sugar maples are native, have brilliant fall color, and are the source of maple syrup, as well as useful hard wood (rock maple). The Norway maple, native to Europe, is considered an invasive plant in the northeast. Its fall color is yellow. When the petiole or bud of the Norway maple is broken a milky sap may be seen. The winged fruit (samaras) of the Norway maple are much larger than those of sugar maple. Both have chartreuse flowers in early spring before the leaves are on the trees. There are many red maples (A. rubrum) in the arboretum of various sizes. This tree likes the moist soil found here. We have planted an Amur maple (A. gianella) and a paperbark maple (A. griseum) as specimen trees. The red-brown exfoliating bark and compound leaves of the paperbark maple are distinguishing characteristics of this ornamental tree. Japanese maples (A. palmatum) are exhibited for their finely dissected leaves in various shades of green or red and their strong yellow or red fall color. A silver maple (A. saccharinium) grows by Diamond Brook.


Chinese chestnut—Castanea mollissima

As American chestnuts succumbed to chestnut blight Chinese chestnut have replaced them as landscape trees, appreciated for their many flowers on 4-5" catkins although some people object to their odor. The nut, not considered as sweet as that of our native chestnut, is contained in a prickly shell (burr). This is a messy tree between flower and fruit drop, but spectacular in flower in June.


American holly—Ilex opaca

There are many specimens of this native holly in the arboretum, most of them “planted” by birds. Female plants may bear abundant dull red berries from October through much of the winter. This holly is classified as a broad-leaved evergreen. Other hollies grown in the arboretum are the deciduous native winterberry (I. verticillata), and Japanese holly (I. crenata) an evergreen species with black fruit that has “escaped” into our woodlands.


weeping willow—Salix alba

Originally from Europe and Asia, the weeping willow has become naturalized in North America. These trees grow well in moist places. They are one of our first trees to show green in the spring and one of the last to drop its leaves in the fall. They grow rapidly and are susceptible to ice and windstorms. They are considered “dirty” trees as leaves, twigs, and branches fall throughout the summer. Our largest specimen is known as “The Duchess. Pussy willows (S. discolor) grow on the west side of the pond.


dawn redwood—Metasequoia glyptrostroboides

A dawn redwood, planted in 1948, marks the center of the arboretum. The soft needles of this deciduous conifer turn orange-brown before they fall. The bark is reddish brown and the trunk of this mature tree has flaring buttresses. Our tree came from an Arnold Arboretum expedition to China to collect seeds. It was known only from the fossil record until 1941.


Japanese umbrella pine—Sciadopitys verticillata

Despite its name this conifer is not a true pine. The “umbrella” part its common name refers to the whorled arrangement of its needles. These slow growing trees make excellent specimen trees when properly sited. It will grow well in full sun.


pecan—Carya illinoinensis

Native to the southern US this specimen is thriving in this site, its northern limit. It bears only a little fruit each year, unlike the pecans grown as horticultural crops in the southeast and southwest. The pecan is a member of the hickory family. There is a bitternut hickory near the Bradford pear. A black walnut (Juglans nigra) grows along Diamond Brook.


dove tree—Davidia involucrata

In May large white flowers may be found on the ground beneath the dove tree. Botanically they are two bracts surrounding the true small flower. The name dove tree comes from a fancied appearance of the bracts to dove tails. Ideally this handsome flowering tree would be exhibited as a specimen. Ours has grown tall and the flowers are difficult to see. Dove trees are native to China.


red oak--Quercus rubra

The red oak is the official tree of the State of New Jersey. We have several specimens of this magnificent oak. Acorns are characteristic of oaks. We have white oaks (Q. alba) and chestnut oaks (Q. prinus) in the white oak group with rounded lobes on the leaves. Members of the black oak group (red oak and pin oak—Q. palustris) have pointed lobes. All of these are native to New Jersey. Red oaks may be identified by “trails” of dark bark on the upper branches. The lower branches of pin oaks are pendulous (downward); the middle branches are horizontal, while the upper branches are upright.


American elm—Ulmus americana

Dutch elm disease did not kill all of the elms in our area. They are native to New Jersey and may be seen along streams, streets, in yards, and in the arboretum by the pond and as a 9-11 memorial near the sidewalk north of the entry road. Elms bear small red flowers in March. Fall leaf color is a deep yellow.


Carolina hemlock—Tsuga caroliniana

There is a large Carolina hemlock in the center of the arboretum and a small Canadian (eastern) hemlock (T. Canadensis) on the edge of the lawn near the arboretum sign. These sister species have been attacked in recent years by the hemlock woolly adelgids and many specimens in parks, forests, and yards have died. There is no replacement for this tree as a hedge, for no other needled evergreen grows so well in the shade or can withstand so much clipping and pruning.


American beech—Fagus grandifolia

The woods of the arboretum are a small remnant of the beech-oak-hickory forest that once covered northern New Jersey. We have many specimens of American beech, a tree that keeps many of its (now golden brown) leaves throughout much of the winter, especially on young trees. The American beech is characterized by its suckering habit. In the north front lawn are two European beech trees (Fagus sylvatica). Its bark is smooth and gray like that of the American beech, but becomes less smooth in old specimens. The European beech does not sucker.


Atlas cedar—Cedrus atlantica

These needled evergreens should be used as specimen trees but are too often found planted too close to buildings. The blue form (blue Atlas cedar—C. a. glauca) has been most popular. The horizontally spreading branches of the mature tree make it attractive. Cedars may be identified by the position of their cones: upright on the upper side of branches.


arborvitae—Thuja occidentalis

This native evergreen is used as a specimen or accent, foundation plant, or planted as a hedge or screen. It requires sun, as do most conifers. There are many cultivars and selection should be made depending on the purpose of the planting. Arborvitae is a favorite food of deer. Color change to a cast of yellow, purple or brown is normal in the winter, with a return to green in the spring. Winter burn due to rapid temperature change, direct sun, wind, or lack of rain in the fall kills foliage that can be pruned off in the spring.


Amur corktree—Phellodendron amurense

This specimen shows the beautiful and unusual ridged-and-furrowed bark on the trunk of an old tree. In an open space it would have an open rounded crown with a few large horizontal branches.


sweetgum—Liquidamber styraciflua

Native sweetgums grow well in the moist soil of the arboretum. We also have planted a specimen. It is easy to identify a sweetgum by its glossy deep green star-shaped leaves with 5 to 7 lobes and fine teeth and by its fruit, a spiky gumball that is difficult to rake up. Stems often have corky wings. Fall color is outstanding: yellows, oranges, purples, and reds.


tuliptree—Liriodendron tulipifera

There are both young and mature specimens of the native tuliptree in the arboretum. It is one of our tallest native trees, over 150', and in woodlands has no side branches for about 80% of its height. When grown in the open, large side branches may touch the ground. Leaf shape is distinctive. Leaves become golden yellow in the fall. The large flowers (2" wide, 2" high) greenish-yellow on the outside, orange on the inside, is somewhat tulip-like. They are often not noticed on tall trees until fallen flowers are seen on the ground in June.


Persian ironwood—Parrotia persica

The tree was selected for our collection because of its small crimson flowers that appear in March before the leaves. Secondly, the older trunks and branches have exfoliated bark in shades of gray, green, white and brown. Fall leaf color is brilliant yellow, orange, or scarlet. The lustrous green leaves of summer and resistance to pests and disease make this a good choice as a small four-season tree.


river birch—Betula nigra

Our cluster of three river birch has been growing rapidly as this native plant grows best is moist streamside locations. This species is the most resistant of the birches to disease and insect problems. The exfoliating bark leaves the attractive inner bark in various shades of brown. When the trees become old the trunk will be brown. Fall leaf color is yellow.


redbud—Cercis canadensis

We have two large redbuds, both beautiful in April when their branches are covered with rosy pink flowers. This native tree has green heart-shaped leaves in summer that turn yellow in the fall. In October the dark brown 2 to 3" long seedpods may be the outstanding feature of the tree.


katsuratree—Cercidiphyllum japonicum

We seldom notice the very small red flowers of the katsura in early April, but grow this tree for the somewhat heart-shaped dark blue-green leaves in summer and yellow fall leaf color.


fringetree—Chionanthus virginicus

We have three fringetrees. Two of them are covered with 6 to 8" long panicles of white flowers in May. The third tree, planted in the woods, does not get enough light to flower. This tree is native to southern New Jersey. We recently planted a Chinese fringetree (C. retusus).


pitch pine—Pinus rigida

Pitch pines were planted throughout the arboretum but are succumbing to borers. With bundles of three needles pitch pines are abundant in the Pine Barrens of New Jersey and Long Island where fire damaged trees produce sprouts. White pines (P. strobus) have bundles of five needles. A specimen of this native pine is on the side of Diamond Brook as is a Japanese black pine (P. thunbergii) that has needles in bundles of two.


English yew—Taxus baccata

Several English yews are found in the arboretum, both deliberately planted and “escaped.” When the deer find our yews the lower branches will be bare. English yews that grow unpruned are the same species used as foundation plants that are subject to severe pruning. They are a favorite tree for topiary work.


Japanese snowbell—(Styrax japonicus)

We have two specimens of Japanese snowbell that are covered with 3/4" wide white flowers on long stalks in May. The leaves do not cover the flowers. In late summer gray-green fruits are seen. The plant near the tool shed grows extraordinarily well considering that it is in shade.


Japanese stewartia—Stewartia pseudocamellia

Yes, stewartia is the common name for this tree that is covered with 2 to 2 1/2" cup-shaped white flowers in July. We are waiting for maturity to see its exfoliating bark. Fall leaf color is yellow, red, to dark red. Stewartias are in the tea family along with our franklinia (Franklinia alatamaha) on the other side of the pond. The franklinia was found in Georgia and is now extinct in the wild. The white cup-shaped flowers bloom in September with some in August and October. The leaves in fall are orange and red.


sourwood—Oxydendrum arboreum

Native south of New Jersey, the oxydendrum bears 4 to 10" long panicles of white flowers in the summer that may cover the tree. After the flowers fade, the yellowish flower stalks with developing fruit make it appear to bloom until fall. The shiny dark green leaves turn yellow, red, or purple in the fall. It makes an excellent specimen tree.


yellowwood—Cladrastis kentukea

Native south of New Jersey the yellowwood growns well here and may reach 50' in height with an equal spread. The bark is smooth and gray. Bright green leaves turn yellow in the fall. The tree’s name comes from the color of the heartwood. Drooping panicles of white flowers cover the tree in early June.


magnolias—Magnolia species

Surrounding the recirculating fountain is magnolia circle with Loebner magnolia (M. x loebneri), sweetbay magnolia (M. virginiana), the magnolia hybrid ‘Elizabeth,’ southern magnolia (M. grandiflora) and a star magnolia (M. stellata). On the front lawn of the arboretum look for a saucer magnolia (M. soulangia).


dogwood—Cornus species

Kousa allee, a double row of C. kousa, extending from the bridge past the gazebo to the recirculating fountain is our outstanding dogwood feature. There are other Kousa dogwoods in the arboretum along with the native flowering dogwood (C. florida), silky dogwood (C. amomum) at the west end of the north front lawn, and red osier dogwood (C. serica), red twig dogwood (C. stolonifera), and Tatarian dogwood (C. alba) all pond side.


spicebush—Lindera benzoin

In early spring the understory of the arboretum glows with the small yellow flowers of our many spicebushes. These native shrubs find ideal growing conditions in the moist soil of the arboretum. In the fall female plants bear bright scarlet fruit. The name spicebush comes from the odor of the leaves when broken. The light green leaves turn golden yellow in the fall.


ginkgo—Ginkgo biloba

Like the metasequoia, the ginkgo was known from fossils before it was known to modern botanists. It too is native to China. The fan-shaped leaves turn yellow in the fall and drop from the tree quickly. Ginkgos are often used as street trees.


sassafras—Sassafras albidium

Sassafras is one of the best native trees for fall color in shades of yellow, orange, scarlet and purple. Sassafras may be distinguished by its bark of deep red-brown flat corky ridges. The leaves in three different shapes (entire, three-lobed and mitten) are different from those of any other tree.


red buckeye—Aesculus pavia

Red buckeye is in the same family as horsechestnut. it has palmately compound leaves, large buds, large leaf scars, and red flowers. it is native to the southeastern US.