Notes on Chestnuts at Windward

Andrew:

A seedling Spanish Chestnut from 2008

For the past several years, Windward has been trying to establish chestnut trees along the top of the a prominent hillside on our property.

Walt has been courteously tending to the trees, as a long-term gift to future generations of the community.

Sadly all the chestnuts we have started have not survived past their first couple of years.

But, perseverance! We are continuing to explore other options.

Species and cultivars of Chestnuts

There are a handful of high-yielding nut-producing chestnuts (Castenea spp.) in the world - primarily from Europe, Asia and the America's. The ones I have found that are hardy to Zone 6 include:

Leaf, unopened husks and nuts of American Chestnuts, C.dentata

I am not certain, but I believe that we have been trying to grow cultivars of C. sativa. Both "Colossal" and some kind of generic variety just called by the common name "Spanish Chestnut".

Most European and Asian chestnuts are blight resistant. At this point it time, the American Chestnut is hardly cultivated in the US because it is not blight resistant. However, there is quite a lot of plant breeding taking place to change this. Many people have reported successful fruit bearing of American Chestnuts West of the Rockies because the blight fungus is not present in remote areas of the west.

If you don't know about why this is important check out this article on Chestnut blight fungus.

The Washington Chestnut Company is primarily growing crosses based on Sweet European Chestnut and Japanese Chestnut. "...providing the sweetness and flavor of the European chestnuts and the large size of the Japanese chestnuts." These folks seem like a good place to look for chestnuts to germinate and grow.

Some Chestnuts, like C.sativa are readily coppiceable. Coppicing can extend the life of the trees, and provide non-food timber for construction and fencing. This is a photo of a C.sativa "coppice with standards" system in the UK.

Different Chestnuts species can have different growth habits, tolerance to soil conditions, drought, and cold, and climatic conditions like light Autumn frosts, or variable spring temperatures. Each has been cultivated for a variety of purposes, and many cultivars exist.

Given all the potential variation it is very important that we understand what species, crosses, and cultivars we are trying to grow.

In general, I see no real benefit to trying to American Chestnuts on the property, when it is known that European, Chinese, Japanese Chestnuts produce well, are similarly large over-story trees, and have little susceptibility to disease.

From my research it appears that the European chestnut is more likely to thrive in our dryland forest, as they originate in temperate Mediterranean environments with cold wet winters and hot dry summers.

Japanese and Chinese Chestnuts appear to not have as much drought tolerance, have more porous leaves and general like cooler moister conditions more akin to western Washington and Oregon.

How to Kill a Chestnut Tree

In researching the issues we've been having with Chestnuts I discovered the Washington Chestnut Company's informative website. They have a page, aptly titled, "How to Kill a Chestnut Tree." It had some points worth sharing.

"Chestnuts will not grow in heavy or clay soils"
This is not so great for us, since we have almost exclusively heavy clay soils.

"Water saturated soils can kill a chestnut tree just about any time a chestnut tree is actively growing."
The primary problem with wet soil is root rot. WCC's website has some good info on how to spot root rot problems.

Dead chestnut tree bud, a result of root rot.
http://www.washingtonchestnut.com/killingtrees.html

"The first sign a chestnut tree has root rot is the new leaves never get full size. Existing leaves will start to brown at the edges. Then all the leaves will turn brown and the tree dies. When a chestnut tree with root rot is dug up, the roots will present weak and rotting roots and the small white fibrous roots will be completely absent."

"Hard frosts after the chestnut trees start to bud out..."
Can significantly set back or kill young trees.

young chestnut leaf with frost damage
http://www.washingtonchestnut.com/killingtrees.html

Unfortunately we have a pattern of warm sunny days and bitter cold clear-skied nights in the early spring. The warm days encourage the sap to start flowing and the buds to begin developing. Having a hard frost at this point can kill and damage all the new growth, setting the tree back.

Mitigating Potential Problems.

There seems to me to be a few things we can do to help mitigate or resolve many of these challenges with chestnuts on our land.

In terms of heavy clay and saturated soils, we can do a lot of up-front work to significantly change the soil conditions before we plant. I will talk about how we are approaching this in a little bit.

A good thing we have already been doing with the Chestnuts is planting them at the top of a hill. This gives them the best natural drainage possible, as gravity ensures that the tops of hills are generally drier than mid and low slopes. This helps with soil water saturation to some degree.

Planting on a hill can also help with potential frost damage since cold air tends to fall down hills, and settle (or get trapped) in low areas on hill sides and in valleys.

This diagram shows where frost tends to accumulate in low places on slopes and in valleys

Planting within an existing coniferous forest also helps with frosts. The evergreen canopy will help intercept cold falling air. Trees are essentially large water pumps. Their bodies are slightly warmer than the surrounding air because they are pulling water up from the earth which maintains a more constant temperature. This us particularly true of evergreen trees in the winter time since they are still actively moving fluids through their trunks and branches.

Chestnuts usually germinate within the protection of an existing forest, so it makes good sense to not go about planting them in open fields or large clearing.

There are some other things that we can do to mitigate frost damage. Such as placing lots of rocks in and around the trees to help capture and store sunlight and conduct the earths heat upwards.

Hugelkultur for Chestnuts

Out primary strategy for building large amounts of high quality humus in the soils under the chestnuts is a technique which I've written about before, Hugelkulture.

In other hugelkulture projects, we have dug level trenches and made liner mounds. For the Chestnuts, we instead dug a very large hole (a crater really). About 10 feet deep and 10 feet around.

We then filled the hole with a mixture of woody biomass, bunny manure, and the clay subsoil which came out of the hole.

The holes are completely filled, and then some. Creating a mound on which a single chestnut tree can be planted, along with supporting species such as comfrey and alfalfa.

We hope that this level of soil amendment will help with the problems of clay soil, as well as provide a deep and substantial reservoir of highly nutritious and moisture retentive soil for the trees to feast upon - minimizing or eliminating the need for us to irrigate and provide soil amendments later on.