Germplasm

In other books and websites on growing chestnuts, you will find long lists with hundreds of chestnut cultivars listed, most of them unavailable for planting for several reasons. 1) They may not be available in your area, 2) They may not really be grown anymore, 3) They are only available for those who have interest in rare trees, 4) They are not available from nurseries in your area or any area, 5) They have proven to be inferior, 6) They were never really available but have been on the list for years and remain on the list, and 7) They work in a specific location, but not all locations. We understand that it is easy to copy and paste a list of chestnut cultivars, but this website is about reality and how to do things right and efficiently. Therefore, we are only listing those cultivars we have watched succeed in Michigan, the cultivars we have in the Michigan State University cultivar trials in Benton Harbor, Clarksville, East Lansing, Jackson or Traverse City. If they have not been grown there, we do not list them. If they succeeded elsewhere, but have not been grown here, we do not list them. This doesn’t mean you cannot try other cultivars when given a chance, but that is your choice. This section ultimately lists some great successes and provides a short list of failed cultivars.

Seedlings or grafted cultivars—what’s the difference?

Don’t plant seedling trees in Michigan. No matter what you hear, see or read on the Internet. If you are a commercial grower in Michigan you cannot afford to plant seedling trees. I still see ads and still hear about a few growers establishing chestnut orchards with “seedling” chestnuts. This is such a waste! A seedling tree is not defined by size or age, but by the fact that it was never grafted. Would you establish a cherry, peach, or apple orchard by dropping a pit or seed into the ground and waiting for the tree to grow? NEVER! Maybe 100 years ago.

Today, all commercial fruit and nut tree orchards are established with cultivars that have been selected by experts for various traits. These cultivars are not produced through seed, but are cloned by grafting/budding onto the stems of seedlings that will support the chosen cultivar. In this manner, a single tree can be copied millions of times by simply cutting small branches from the chosen tree and attaching it onto the stem of planted seedlings. The branch that is cut from the chosen tree is called the scion wood and the tree to which it is attached is called the rootstock. The rootstock will be from a seed that was planted for the purpose of grafting.

If you purchase a seedling and promise yourself you will graft it sooner or later, please re-consider. Most people never take the time or have the impetus to graft the trees and you will soon find yourself in a situation where your orchard is producing less than 10 percent of what it could have produced. Please do not plant seedlings in Michigan. When rootstock is left un-grafted, less than 50 percent of the trees will go into production in any given year and of those, only 10 percent will be worthy of your resources in terms of fertilizing, irrigating, harvesting and time (Figure 1).

Please do not plant seedlings in Michigan. It will take the trees 8 to 12 years to go into production because physiologically, the trees need to go through seedling and juvenile stages, which can take several years. Grafted trees are normally considered mature trees no matter how young, and can produce nuts in 2 to 3 years after planting. Consider yourself forewarned, if you plant seedling trees.

European X Japanese hybrid
Figure 1. A European X Japanese hybrid cultivar called ‘Colossal’ in the foreground (right) with burs about 6 years after planting and a 10-year-old Chinese chestnut seedling tree (meaning non-grafted) in center without any burs. This is an example of choosing the right germplasm for your orchard. Photo from MSU Traverse City Experiment Station.

Different chestnut species

Generally, there are three species of chestnut that contribute to the genetic makeup of chestnut trees planted in orchards. The species from which cultivars have been selected are those that have a long history of chestnut cultivation, including the Chinese chestnut, the Japanese chestnut (and its subspecies, Korean chestnut) and the European chestnut (Castanea mollissima, C. crenata, and C. sativa, respectively). Some of today’s cultivars are actually hybrids or crosses among these three species. The species can appear similar looking at first, after all they are all edible chestnuts, but using differences such as leaf shape, leaf hairs, stem anatomy and nut characteristics, one can soon begin to tell them apart. Certainly, the hybrids between these trees are difficult to tell apart from the parents that helped form them. Today, we rely on DNA analysis to tell the species and cultivars apart with accuracy.

What is a cultivar?

A cultivar is a word used to differentiate genetic material with certain identifiable traits that can be copied or cloned by grafting to produce identical copies. A well-known story is the ‘Navel’ orange tree. One of it traits is that it does not produce seed. Without seed, how was it propagated? Like all horticultural stock—it was grafted. The scion from the ‘Navel’ orange was cut from the original tree in Brazil and sent to California where is was grafted to rootstock and this original, first-grafted tree can still be viewed (called the ‘Washington Navel’ orange tree) in Riverside, California. Millions of ‘Navel’ orange trees have come from this single mother tree sitting in an intersection in Riverside, California.

There are several methods to attach scion wood to rootstocks and some methods may work better than others for different tree species or under different conditions. For example, budding is a type of grafting where just the bud from the chosen tree is placed within the bark of the rootstock. The scion in this case would be the bud. Chestnuts are commonly grafted with scion wood or with buds, but in either case, the scion will produce trees identical to each other. Once the scion’s bud has sprouted and produced substantial growth, the rootstock above the point of scion attachment will be removed so the scion becomes the only growing material above the point of scion attachment.

If you are following the ideas presented so far, then you will realize that planting seed will produce the rootstock to which the scion is attached and therefore, one rootstock will be genetically distinct from any other rootstock. Therefore, even if the scion is the same throughout the orchard, the rootstock will be genetically distinct from tree to tree. This is one reason why trees planted in an orchard will still show some variability. The genetic diversity of the rootstock can be ignored in most situations, but there have been several cases where rootstock variation has lead to problems as minimal as bark discoloration or as serious as graft union failure and early tree death. In plant systems that have been studied for several decades, the knowledge of rootstock and scion wood combinations can lead to important orchard management opportunities such as rootstock that can lead to the preferential dwarfing of scion growth or resistance to soil-borne root diseases.

We are far away from that level of genetic management in rootstock development of chestnut, but we do believe that fewer problems will develop when the rootstock and scion wood are genetically related. If this theory holds true, then Chinese chestnut cultivars should not be grafted to European/Japanese seedlings or American chestnut and vice versa. That does not mean you can’t do it or shouldn’t try it in experimental situations, but it does mean that unless further research points a new direction, commercial orchards should be established with trees produced by closely related rootstock and scion wood.

Benefits of using cultivars compared to seedling trees

  1. Cultivars are predictable in performance (even if not now, they will be once you learn more about them). 

  2. Cultivars should be placed in the orchard based on their predicable characteristics (e.g., harvest time, pollen production, nut size).
  3. Every tree you plant in the orchard, when planting specific cultivars, should perform the same way in the orchard (see number 1, above).
  4. Regardless of their size or age, grafted cultivars are mature when planted and therefore initiate nut production in Michigan much sooner than seedlings.

  5. Since cultivars are mature, they usually drop leaves at the appropriate time in the autumn. Since seedling trees are immature they have a tendency to hold onto leaves well into winter which can accumulate ice and snow which can break limbs.

  6. 
With a cultivar, you can talk about the traits of your trees; your likes and dislikes, and change out the cultivars to something that fits your needs.

Frequently overheard excuses for not planting cultivars

  1. Cultivars are expensive. They seem expensive at first, because they usually cost more than seedlings; however, you should recover this cost within the first 6 years after planting (see number 4 in Benefits, above).

  2. Cultivars die. Cultivars can die and it is awful to lose an expensive tree. However, they can be grafted again if sprouts are produced. However, using seedlings as an alternative is not an answer. Most seedlings trees in Michigan will not produce nuts for many years, and some seedlings will never produce nuts. The pattern that has been seen over and over again is this: More than 50 percent of the trees in a seedling orchard do not produce nuts. Those trees that do finally go into production will take many years before significant production is observed. Those trees that finally go into production will be variable in terms of commercial quality. The university and various nurseries are working hard to find ways of helping all grafted trees survive planting and live long productive lives. New methods of growing rootstock might help this as the roots will be more fibrous which is thought to benefit survival.
  3. Grafted trees get chestnut blight. That has nothing to do with grafted trees as it depends on the species and cultivar and does not have much to do with the fact that they are grafted or not. You can plant grafted cultivars that are completely resistant to chestnut blight and you can plant seedlings that are very susceptible to chestnut blight. Many of the seedling trees for sale at nurseries right here in Michigan are chestnut blight susceptible—even if Chinese—because some of these Chinese chestnut seedling trees had American chestnut as fathers making the offspring 50% susceptible to the blight. If someone is selling Colossal-seedling trees, they are selling you chestnut trees where 50% of the genetics are unknown AND they will be blight susceptible. Why would you purchase these for a commercial orchard? 

  4. They don’t taste good. Again, this is a case of miss-information. This is probably referring to tasting nuts of the cultivar ‘Colossal’ right from the tree. When a ‘Colossal’ grafted nut falls fresh from the tree, it usually does not taste as good as a Chinese (grafted or ungrafted) nut that falls fresh from the tree. But given a couple of weeks in refrigeration, the process of curing begins and the starches begin to turn to sugar. Grafted ‘Colossal’ chestnuts have been some of the most sought after chestnuts in local grocery stores due to size and taste, combined. In a Missouri taste test, Michigan-grown ‘Colossal’ nuts were considered the sweetest nuts of the entire test beating out Chinese chestnuts and other ‘Colossal’ nuts from California and Missouri (See Post Scripts at the end of this Handbook).

Common chestnut cultivars grown in Michigan and why they are suggested

The following chestnut cultivars have been planted in various locations in Michigan and have grown and produced good yields of nuts. We emphasize planting these cultivars based on the fact that the cultivars have grown and yielded well in our experimental plots. However, there may be hundreds of cultivars that might do that. We suggest these cultivars because of the single beneficial trait or characteristic that is listed for each cultivar. As you read about the cultivars below, look for the bold and underlined statement that provides the single (or two) most important characteristic that cultivar will provide you. If that is not important to you, then you may not want to plant that cultivar. For example, if I were growing chestnut trees in northern Michigan, around the 45th parallel (Traverse City), I would want to place ‘Precoce Migoule’ and ‘Labor Day’ into my orchard. I would still want ‘Colossal’, the highest yielding cultivar, but I could use both ‘Precoce Migoule’ and ‘Labor Day’ to pollinize the ‘Colossal’ trees. ‘Precoce Migoule’ and ‘Labor Day’ could pollinize each other and they would drop their nuts before ‘Colossal’ and usually before the earliest autumn frost. However, if I was really concerned with chestnut blight disease, I would stay away from ‘Colossal’, and ‘Precoce Migoule’ since these are blight susceptible and instead, I would consider planting high yielding Chinese chestnut cultivars such as ‘Benton Harbor’.

Where to purchase these grafted trees selected for Michigan

Currently, we are working closely with Forrest Keeling Nursery in Elsberry, Missouri. We send them our seed and scion wood and they graft the trees and sell them to Michigan growers. They recommend fall planting of their stock and so far this seems to have been successful. Read about the care they take in producing these trees. You can purchase from other nurseries if they are growing the same cultivars. 

Forrest Keeling University
Forrest Keeling Nursery