On October 23-24, the Arboretum hosted the 5th Annual International Maple Symposium. This symposium included speakers and attendees from across North America and Europe was sold out. The symposium occurs every three years and rotates among North America, Europe, and Asia. This year, held at the Morris Arboretum of the University of Pennsylvania, was an excellent opportunity to showcase the Arboretum’s highly regarded maple collection, and introduce a number of new visitors to the garden. Along with a lineup of internationally recognized maple experts, the symposium featured garden tours to both public and private gardens.

Anthony Aiello, Morris Arboretum’s Gayle E. Maloney director of horticulture and curator, had this to say about the Arboretum’s maple collection: “Each fall I look forward to the succession of colors that maples (Acer) bring. This large group of plants is adapted to a wide range of conditions and can be found growing throughout the Northern hemisphere. Maples have been long valued by horticulturists as superior garden plants. As a result, there are maples that are adapted to a wide range of growing conditions and suitable for a variety of landscapes. Several maple species are native to Pennsylvania, some of which are highly desirable as ornamental trees, while others are best suited for natural areas. As you explore the Arboretum or natural areas throughout the state, look for these native species of maple:

Acer saccharum – sugar maple

Perhaps the best known native species is sugar maple, famous as the source of maple syrup, excellent lumber, and its array of spectacular autumn leaf fall color. Sugar maples are native throughout the state as a component of the northern deciduous forest. They are best used as lawn or park trees, and grow upwards of 90 feet, making them excellent shade trees when given adequate space. There are a number of varieties selected for their excellent fall color and these include Bonfire and Green Mountain (‘PNI 0285’). At Morris Arboretum there are sugar maples growing on the Holly Slope, along Meadowbrook Avenue and throughout the natural areas.

Acer rubrum – red maple

Also known for its outstanding fall color, red maple is the most common tree in Pennsylvania, growing in a variety of habitats. Red maples grow best in slightly acidic soils and can be chlorotic when grown in more urban or stressful situations. As their names suggests, red maples are best known for their scarlet fall color, and the number of varieties selected for their fall color are too numerous to list. Here at the Arboretum I am especially fond of several old trees that grow along the East Brook near the Log Cabin. In recent years we have planted the varieties Red Sunset (‘Franksred’) and October Glory (PNI-0268’) near the wetland and along Paper Mill Run.

Acer saccharinum – silver maple

Closely related to red maple, silver maple is the largest of our native maples, growing up to 100 feet. It occurs throughout the state along streams and rivers. Although silver maples are regularly planted as shade trees because of their rapid growth, they are not well-suited to this function; because of their fast growth and irregular branching, they tend to be weak-wooded and subject to branch breakage. Although I would not recommend planting silver maples close to your home, they are wonderful plants when found growing naturally, and the silver undersides of their leaves together with their shaggy bark are especially attractive. Look for a beautiful specimen next to the bridge when you enter the Morris Arboretum.

Acer × fremanii – Freeman maple

Although not strictly a Pennsylvanian native, I should mention this hybrid of silver and red maple. There are several varieties that have been selected for having the best attributes of both parents – the fall color of red maple together with the adaptability of silver maple. Among the best known of these selections are Autumn Blaze (‘Jeffersred’) and Autumn Fantasy (‘DTR 102’), both of which make handsome large shade or street trees with good orange to red fall color.

Acer penylvanicum - moosewood

Maple enthusiasts will wax poetic and argue endlessly about a group of maples called the “snakebarks” for their smooth green bark that is accented with white markings. All of the snakebark maples are from Asia, except for moosewood, which grows throughout eastern North America, and occurs commonly throughout central and northern Pennsylvania. A small tree that grows upwards of 30 feet, moosewood does not grow particularly well in our part of the state. For best results in our area, trees should be grown in a favorable site, with moist, well-drained and slightly acidic soil.

Acer spicatum¬ – mountain maple

Mountain maple is a small multi-stemmed understory tree that is found mostly in northern Pennsylvania but also at higher elevations elsewhere in the state. It has pleasing yellow to orange to red fall color, but natural populations have been heavily impacted by deer browsing. It is rarely if ever available commercially, but is well worth preserving and encouraging where it occurs naturally.

As everyone knows, one of the grandest spectacles in fall is watching the colors change on our native maples, and a drive throughout Pennsylvania or New England provides one of the most magnificent displays that nature has to offer. This fall, come to the Morris Arboretum and enjoy what our native maples have to offer.”

Anthony Aiello, The Gayle E. Mahoney Director of Horticulture/Morris Arboretum of the University of Pennsylvania

For more information on Pennsylvanian native maples, along with many others, an excellent resource is Trees of Pennsylvania, by the Arboretum’s Ann Rhoads and Timothy Block.