Campus Horticulturists Hope to Save Remarkable Tree’s Genes

Tim Mercer with redbud tree
Tim Mercer, head grower, is working to grow another Eastern redbud with the same genetic traits as one already existing on campus.
Redbud tree wrap
A method called “air layering” is being used to attempt to grow another Eastern redbud.

You would never know by looking at it now, but one of the Eastern redbud trees on campus is a former Massachusetts State Champion Tree, once measured the largest specimen of its species by three combined features – diameter at chest height, overall height and crown spread. Today, damaged by storms, it’s only about 12 feet tall, but it is still very valuable to the horticulturists who care for the campus’s plants and trees. 

“It doesn’t look like much now but it once was a glorious tree,” says Todd Cournoyer, head of landscape management. “You’ll never see another redbud in Massachusetts that size. It’s a rarity and an exceptional specimen.”

The Eastern redbud (Cercis canadensis) is generally considered a small tree, says head grower Tim Mercer. It is native to the Mid-Atlantic and southern states and woodlands of places like Pennsylvania, and is at the threshold of its cold tolerance in our state, he adds. Because the tree on campus is obviously cold-hardy and because of its remarkable size, likely taller than 50 feet in its heyday, he notes, “It has tremendous genetic potential to grow into another very large tree, if we can find a way to grow a new one.”

Last year, Mercer began to collect seed pods from the once-grand old tree, but he acknowledges that growing a new tree from seed is a long shot. “I’ve grown out about 70 seedlings so far, but the question is will those offspring express the same genetic traits as the parent tree. They are not clones but they do contain genes of the mother tree and may show promise.” Another method of propagation that does produce a clone is cuttings but many woody plants, especially older trees, don’t root well from a cutting, he explains. His attempt to root cuttings last summer was unsuccessful.

Before the redbud project came up, Mercer recalls, a former summer student intern, Lee Michalopaulos, who worked with the groundskeepers to create the campus’s Songbird Garden two years ago and is now a member of the landscape team, mentioned a propagation method known as air layering that has had success with woody plants. “That put the thought into my head,” says Mercer. With air-layering, the stem is wounded in a prescribed way and the wound is wrapped with growing media and damp mossor coconut fiber, then cocooned in a protective moisture-retaining wrap to encourage roots to format the wound site, he explains.

Because the wound prevents the carbohydrates produced above the cut from moving any farther down, it provides nutrition to form new roots at the wound site, Mercer notes. Water can still move up the stem from the tree’s roots through the inner layers of the tree. “When you open this and see little roots, you can then cut the branch and plant it,” he adds. That hasn’t happened yet this year, the grower says, probably because of timing.” But now, armed with newly discovered information from an old U.S. Forest Service bulletin on air layering, he states, “next year we’ll get it right.”