Man has green thumb with rare-to-Minnesota trees

• Tree

Julie buntjer/daily globe Walter Willey of rural Worthington stands next to one of the eight common horse-chestnut trees on his acreage. The tree is considered quite rare in Minnesota, but is found in other areas of the country.

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WORTHINGTON — Standing in the back yard of his rural Worthington home, Walter Willey points to an assortment of tree varieties. A giant hackberry tree towers over everything, from the pussy willow to the quaking aspen, locust, catalpa, maple, red maple and walnut trees scattered throughout the property.

Willey’s favorite — and likely rarest — tree growing on the homestead is the common horse-chestnut. He hasn’t found any others growing in this part of the state. In fact, the only other place he’s seen them is at the Minnesota Landscape Arboretum in Chaska.

The horse-chestnut tree is often confused with the Ohio Buckeye, which is commonly grown throughout Minnesota.

“The flowers look about the same, and the nuts look almost identical,” said Willey. “The leaf (of the buckeye) comes to a point — that’s the main difference.”

With a common horse-chestnut tree (Aesculus hippocastanum) on one side of his driveway and an Ohio Buckeye (Aesculus glabra) on the other, it’s easy to see the difference between the two — and just as easy to see the similarities. The trees are members of the same genus — the horse-chestnut is the Eurasian species, and the buckeye is the North American species.

Willey first discovered the common horse-chestnut tree growing on his property after he and his wife, Kathy, moved there in 1968. A few years later, he wrote to Leon Snyder, one of his professors at the University of Minnesota, to inquire about its rarity in Minnesota. Willey still has the letter, dated March 6, 1975, in which Snyder writes, “The horse-chestnut is a rare tree in Minnesota. I know of only about one-half dozen growing in the state.”

Snyder said in the letter that he was surprised to hear of one growing near Worthington. The others he had seen were located in the Twin Cities and in southeast Minnesota.

Peter Moe, director of operations for the Minnesota Landscape Arboretum, said the common horse-chestnut is likely just as rare in Minnesota today as it was 36 years ago when Snyder sent his letter to Willey.

“It is still a very uncommonly planted tree,” said Moe. “We’ve had trouble getting them established at the arboretum.”

Though the arboretum has “a few” common horse-chestnuts, Moe said some were lost to winter injury, while others have “just plain died.”

The biggest challenge for growing them in Minnesota is that the tree is considered hardy to Zone 5, while southern Minnesota is Zone 4.

“They just have not performed well. They are very rarely planted in the Twin Cities,” said Moe.

On the other hand, the trees are quite common in states to the south. Even in Wisconsin, where Zone 4 follows up the eastern side of the state, the common horse-chestnut is popular.

The tree Willey referenced in his letter to Snyder is known now as the mother tree. It died about a decade ago, but not before producing many seeds.

“One year I had a lot of them — I had 99 that grew,” Willey said. “But, the deer just love them. They just wiped them out, practically. They eat the buds off all the time.”

Since then, Willey has become rather protective of his horse-chestnut trees. As seedlings, the trees are surrounded by deer-proof wire or mesh fencing to protect the delicate buds, and as they get older, he keeps plastic tile around the trunks to protect the bark from being damaged by mice.

Today, Willey has eight common horse-chestnut trees growing in his yard, and he hopes to collect more nuts this fall to plant the seeds. As word has spread about the tree, however, he’s already fielding requests for seed.

The common horse-chestnut, according to Willey’s well-used copy of “Field Guide and Natural History to Trees of North America,” is widely used as an ornamental and shade tree. Extracts from the leaves, fruits and seeds have been used as medicines and as poisons, he read.

While the common horse-chestnut can grow to a height of 80 feet, the mother tree on the Willey homestead was only about one-fourth that size. The tree near his driveway is estimated at just 15 to 20 feet tall.

The trees bloom in late May, and after about 10 years of growth, begin to produce nuts encased in shells that are about the size of golf balls with sharp thorns around the outside covering.

“Some people don’t like them because people think the nuts are messy,” said Moe. “They do have pretty flowers. If (Willey) is willing to keep them growing, that is valuable. He does have something that I think very few people in Minnesota have.”

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