by Marty Green ·
Friday, July 10, 2026
Brian McClain hand pollinates a chestnut tree flower, or catkin (below), with pollen spores on a slide. (Photos by Lisa Aciukewicz
About this time two years ago, something happened that hadn’t been seen in Harvard for 75 years or more. Several American chestnut trees came into bloom. They bloomed again in 2025 and are blooming now at a nursery orchard created by Harvard resident Brian McClain as part of a widespread effort to bring American chestnuts back to the forest.
Chestnuts once dominated the eastern American woodlands. Taller than oaks, they have been called the redwoods of the east. About 4 billion of them grew in forests from Maine to Mississippi, until they were struck by a fungal blight that began around 1900. By the 1950s, American chestnuts were functionally extinct; while many young saplings still sprouted from old roots, they never grew to maturity or flowered and produced nuts in natural forest conditions.
In 2019, McClain got permission from the Conservation Commission to create a chestnut orchard at the Powell conservation land on East Bare Hill Road. Starting in 2020, he planted 100 young trees, first with nuts from Massachusetts stock and later with nuts from states ranging from Georgia to Vermont. His goal, he wrote in an email, was “to represent as much of the genetic diversity of the entire chestnut range as possible.”
By 2024, the young chestnut trees were mature enough to flower, their creamy-white blossoms trailing in long catkins. McClain hand-pollinated the blossoms with transgenic pollen supplied by the University of New England in Biddeford, Maine. This pollen has a blight-resistant gene derived from wheat. That first year, the trees produced 95 chestnuts, about half of which would have inherited the resistant gene. In 2025, the trees produced 390 nuts, and McClain expects about 400 this year.
The orchard chestnuts carry both male and female flowers. But, because these trees do not themselves have the resistant gene, hand pollination is needed every year to provide resistance to the next generation that will grow from the nuts. So McClain covers the female flowers with plastic bags he jokingly refers to as “chastity belts” to prevent pollination from trees within the orchard. McClain has a coding system for seven different types of pollen, again to provide genetic diversity.
Hand-pollination is a labor-intensive process. McClain opens a small cooler and takes out a glass slide, which is covered with the transgenic pollen. He moistens the slide with a spray bottle of water. Then, carrying the slide, he climbs a 20-foot aluminum orchard ladder, removes the bag from a female flower, and applies the pollen. And then he moves on to the next blossom and repeats the process, time after time.
McClain’s advice about climbing the tall, narrow, three-legged ladder: “Don’t look down!”
This fall these chestnut trees will produce nuts from the pollinated blossoms. McClain will send them to the research center at the University of New England, as he has done for the past two years. It is not yet possible to try planting the resistant nuts except in controlled research areas. The U.S. Department of Agriculture, the Food and Drug Administration, and the Environmental Protection Agency must all declare these transgenic trees—known as the Darling-54 chestnuts—safe for the environment before the resistant nuts can be planted except in research plots.
Some of the Harvard orchard’s 6-year-old trees have grown strongly. The biggest is 30 feet tall with a trunk about 7 inches in diameter. The dry, sunny orchard setting helps to keep the trees healthy longer, because the blight fungus thrives in shade and dampness. But these orchard trees are not resistant to the blight, even though trees grown from their seed may be. Many of the young trees in the orchard now show signs of blight—dead branches, scarred bark, browning leaves. Some have died, and McClain has cut them down. But then new sprouts grow up from the living roots, just as still happens in the wild from roots that may go back hundreds of years.
Petri Flint stands next to a chestnut ghost in Harvard. Chestnuts are rot resistant and thus these ghosts can still be found in the forest. This tree was estimated to be about 400 years old so it was a sturdy young tree in the 1600s. It died of blight about 100 years ago. (Courtesy photo)