Chestnuts: Growing the American Chestnut Tree

Wiped out by blight in the early 20th century, resistant hybrids of the American chestnut tree are making a comeback. Their rapid growth and productivity make them an excellent addition to any homestead.
February/March 2010
http://www.motherearthnews.com/organic-gardening/american-chestnut-tree-zmaz10fmzraw.aspx
A chestnut orchard at Delmarvelous Farms in Townsend, DE. Whether you're growing American chestnut trees or a related species, give each tree about 40 feet of space in all directions.


PHOTO: RONALD SALMON

The majestic American chestnut tree was once common throughout the forests of eastern North America, providing sweet, meaty chestnuts for humans and wildlife. A fungus first noted in the United States in 1904 quickly wiped out this native species, but fortunately we can still grow our own chestnuts today because the American chestnut’s Chinese cousin is resistant to the blight that devastated the American species.

I planted my chestnut trees here in New Paltz, N.Y., in 1997. I had a relatively small area to devote to chestnuts, and, except for one tree, I chose grafted hybrid varieties that produce large nuts, are resistant to chestnut blight, and are cold-hardy (because the temperature here in New York’s Hudson Valley can plummet to minus 25 degrees Fahrenheit). The varieties I planted were ‘Bisalta #3,’ ‘Colossal,’ ‘Eaton,’ ‘Marigoule’ and ‘Mossberg.’

Given suitable soil and site conditions, Chinese chestnuts and their hybrids grow quickly and start to bear at a young age — typically about their fourth year. My largest and quickest-to-bear tree, now 12 years old, was actually grown by planting a Chinese chestnut. The tree has both a height and spread of about 20 feet, and it yields more than half a bushel of chestnuts every season. It’s a beauty, as chestnut trees generally are, with nice form and leaves that retain a fresh glossiness before turning a rich, golden brown in autumn. Chestnut trees can be “luscious landscaping” for any yard, as long as they’re not planted where the sharp burrs that cover the nuts could cause problems when they drop.

Planning and Early Care

Chestnut trees need abundant sunlight (six or more hours of direct summer sun) and fertile, well-drained and slightly acidic soil. Generally, plan on giving a chestnut tree about 40 feet of room in all directions. If you’re in a rush for large harvests, plant at half that distance and remove every other tree when they start to crowd each other. You must plant two trees to provide the necessary cross-pollination, so, unless your neighbor has a tree that’s a seedling or is of a different variety, always plant two different varieties. Chestnuts are primarily wind-pollinated, so the two or more pollenizers need to be within about 200 feet of each other.

Chestnut trees require little care beyond their formative stage. While they’re young, ensure adequate branch spacing by training the trees to follow what’s known as the modified central leader form. This promotes growth of a single, upright main stem by pinching back, bending down, or cutting off any competitors for that top position. Select major scaffold limbs growing off the main stem, spacing them a foot or more apart up along the central leader. Scaffold limbs should originate from a spiral arrangement as much as possible so that no limb is directly above the one below it. Start the lowest scaffold limb high enough that you can mow under the tree. After the central leader reaches 6 to 8 feet in height, cut it back to a side branch to allow subsequent tree growth to spread wide. Chinese chestnut trees have naturally good form, so not much pruning is needed to get the growth described here.

Chestnut Blight

Chestnut blight, a fungus that originated in Asia, was first noted in the United States in 1904 at the New York Zoological Garden. Within 50 years, the disease had infected almost all American chestnut trees.

Chestnut blight kills only the aboveground portion of chestnut trees, so infected trees that are killed back to the ground resprout only to become infected again, keeping the fungus active. Unless some naturally blight-resistant American chestnut trees are found hidden in an eastern forest (many people have been looking), native chestnuts would grow into timber-size specimens with good edible nuts only in areas in the Midwest and West that have been shielded from the spread of chestnut blight.

It can be difficult to know whether the infective agent is present in your area. Because it can take 10 years or longer for a tree to develop blight symptoms, it’s a gamble to plant American chestnut trees, even in the Midwest and West.

In Europe, the chestnut blight organism has been controlled by infecting the organism with a virus that weakens it so that trees can better resist it.

Harvesting Chestnuts

For better and for worse, chestnuts come inside prickly burrs, each more or less the size of a tennis ball (depending on the variety and the growing conditions) and housing one to three nuts. The “for better” part is that those spiny burrs usually keep squirrels at bay. The “for worse” part is that we humans also have to deal with the burrs.

When chestnuts are ripe, burrs either drop to the ground, nuts within, or open to release the nuts and then drop themselves. Either way, you end up with the ground full of spiny burrs, so shoes are a must when walking under chestnut trees. Squirrels will gather nuts that have been released from burrs, so I pick ripe nuts and fallen, full burrs from the ground every day or two. I help things along by knocking loose burrs off branches with a pole, or by shaking whole limbs. Don’t stand beneath shaking limbs or you’ll be bopped by spiny orbs! Unopened, dropped burrs will mature and open at cool temperatures with high humidity. After you remove the nuts, you can use the burrs as mulch in areas where you want to deter squirrels, raccoons, and other tender-footed pests.

Post-harvest Necessities

The easiest part of growing chestnuts is growing the trees and harvesting the nuts. More deliberate attention is needed to get those nuts into condition for eating. You need three things: avoidance of chestnut weevils, correct curing, and suitable storage. The first step is to mow beneath the trees to make finding dropped nuts easier.

Chestnut weevils lay eggs in burrs in mid to late summer and are common throughout North America. The larvae hatch, eat, then exit the nuts after they drop. The weevils overwinter for one to three years in the soil before emerging and laying eggs again. Tiny holes in chestnut shells are the goodbye wave of the weevil.

My goals are to limit weevil population buildup and keep in edible condition those nuts in which weevils have laid eggs. I reduce the weevil population by picking up fallen nuts daily (or at least every other day) to prevent weevils in infested nuts from entering the soil. Letting chickens or guinea hens forage beneath trees also helps keep weevil populations in check.

Killing insect eggs or small larvae already within nuts keeps the nuts in edible condition. To do this, put the nuts (after they have been removed from their burrs) in water held at 120 degrees for 20 minutes. Immediately after their water bath, dry the nuts in the sun between wire mesh screens, or somewhere outside that is safe from squirrels.

When the nuts are dry, refrigerate them, or store them in a dry, cool spot (less than 40 degrees). Chestnuts are unique among nuts in that their nutmeat is high in carbohydrates, rather than high in oil. The nuts are rather bland at harvest, but after a few days in the refrigerator, some of the starches change to flavorful sugars.

For long-term storage of nuts, avoid both mold and excessive drying. Mold will render nuts inedible, while excessive drying hardens them. Hardened nuts are still edible and can be ground into flour or reconstituted by soaking or cooking in water. Ideal storage conditions are temperatures just above freezing with high humidity, such as in dry peat moss or sawdust in a closed plastic bag that’s then put in a refrigerator or cold root cellar.

I’ve had success keeping chestnuts in wooden boxes at near-freezing temperatures in the garage. My favorite way to prepare them is to make a slit along one side of the shells, roast them, peel off the shells and eat the nuts while still warm. Roast chestnuts in an oven or toaster oven at 400 degrees for about 30 minutes, or in a pan over a woodstove or fire.


Choosing a Chestnut Species

The most common edible chestnut species are the American chestnut (Castanea dentata), Chinese chestnut (C. mollissima), Japanese chestnut (C. crenata) and European chestnut (C. sativa).

Chinese chestnuts are generally hardy to Zone 5, but some are hardy to Zone 3. European and Japanese species are hardy to Zone 5, and American chestnuts are hardy to Zone 3. Chinese chestnuts are the most blight-resistant, the Japanese chestnut is slightly resistant, and the two others are more susceptible to blight. At the extremes in tree structure are the American chestnut, which is tall and upright, and the Chinese chestnut, which has wide-spreading branches.

The nuts of different species are equally variable. American chestnuts are small, have an easily removable pellicle (the thin brown skin around the nutmeat), and are the sweetest of the edible chestnuts. European species have a variable, usually mild flavor, and Japanese chestnuts are sometimes bitter. Chinese chestnuts have a smooth, subtly sweet flavor.

Good flavor, growth habit, and blight resistance all make a strong case for planting Chinese chestnuts or their hybrids. In fact, many chestnut varieties are hybrids representing two or more species, and tree form and size will, to some degree, reflect that parentage.


Great Chestnut Varieties

Colossal: This European/Japanese hybrid has an upright habit and produces large nuts. It is moderately susceptible to blight.

Dunstan Hybrid: This variety is a hybrid of American and Chinese chestnuts. Seedling trees with an upright growth habit consistently bear medium to large, sweet nuts.

Eaton: Likely a seedling of ‘Sleeping Giant’ (a hybrid of American, Chinese and Japanese chestnuts), ‘Eaton’ has a spreading habit with ornamental, glossy leaves. It produces medium to large nuts that ripen early. Nuts have terrific flavor and sweetness and store well, but can be small if conditions aren’t ideal (too wet, too dry or poor soil).

Mossberg: A Chinese variety with large nuts that peel well.

Qing: Pronounced “ching,” this pure Chinese species (the original tree was planted in western Kentucky with Chinese seed) has a spreading habit and ripens midseason. ‘Qing’ produces large, shiny, medium- to dark-mahogany nuts. Nuts are easy to peel, have an excellent, sweet flavor, and an excellent keeping quality (three to four months). ‘Qing’ is a heavy producer, and can actually set too many nuts, which causes reduced nut size. Note: Delayed graft failure, in which the graft seems to be successful but breaks off after a few years, can be a problem with this variety.

Peach: This pure Chinese variety has an upright habit and ripens midseason. It yields medium to large nuts with a slight (edible) peach fuzz on them.


Chestnut Resources

CHESTNUT TREE SOURCES

Burnt Ridge Nursery
Chestnut Hill Tree Farm
Empire Chestnut Co.
Nolin River Nut Tree Nursery

MORE CHESTNUT INFORMATION

The American Chestnut Foundation
Chestnut Growers of America
Northern Nut Growers Association


Lee Reich holds a doctorate in horticulture. His most recent books are Landscaping with Fruit and The Pruning Book.