Pruning chestnuts is an important part of healthy orchard maintenance. There are a couple of reasons to prune your trees, 1) to get the shape and upward growth you need, and 2) for production. Sometimes it seems these are in conflict, as most pruning will initially reduce production, but if done correctly, it will help optimize production.
To achieve both shape and good production, think of the root system of the new tree as a water pump. Any stems greater than ½ the size of the main stem should be considered “leaks” in the main water pipe (see pic). Any stem over ½ the size of the main stem is stealing water from the main stem you are trying to push. The shoot, which you are pushing, will become an extension of the main stem.
Branches smaller than ½ the size of the main stem can stay, as they do not significantly reduce the amount of water to the top of the tree (Photo 2). Pruning and training of a young tree should begin the first year after transplanting. Training should take place gradually over several years and no more pruning should be done than is necessary to enhance the natural shape or structural strength of the tree (Photo 2). The objective in the first few years is to identify and correct problems with the main framework of the tree. Most trees are grown with one central leader (the top most vertical branch). When a young tree has competing leaders, the weaker ones should be removed. If they are essentially equal, either can be removed.
Photo 1. A two-year-old chestnut tree, planted without any pruning. Secondary branches are taking over the central leader, as the tree was never trained. In its second year, a severe crotch has developed, making it difficult to tell which stem is the leader.
Photo 2. A tree similar to that in Photo 1 but in this case, the two-year-old tree received early pruning. The following year the lateral branches under the main leader stem will be removed even though they have burs. These branches are too low to maintain a good shape to the tree, which needs to be trained “upward.”
Photo 3. Pruning demonstration in a grower’s orchard where a discussion ensues about the pruning the tree is about to have. The Photo shows the “before” and “after” pruning process. Notice the small growth tube which is acting as a tree (mouse) guard, not a growth tube.
Another theory on early pruning suggests that the tree should just be allowed to branch and that training should occur a couple years later. This is the method most often used by default. If you don’t prune or are afraid of pruning too much you generally end up following this technique and the results can be seen in Photo 5.
As mentioned above, pruning and training should start when trees are young. This will prevent many serious problems before they develop. Older, neglected trees are more difficult, dangerous, and expensive to prune (Photo 5).
Photo 4. As you can see in the photos, Forrest Keeling Nursery trees are easy to plant and easy to train.
Older trees should be pruned when they are dormant; there is less weight on the limbs. At this time, it is easier to see the framework of the branches. Pruning of young trees should be done when problems can be observed. Also, it is important to mention that properly trained and pruned trees will yield high quality nuts much earlier and overall the health of the tree will be very significant and last longer. Always remember that the primary objective of training and pruning is to develop a strong tree framework that will support nut production. A well-pruned orchard will ensure good orchard management.
Photo 5. An 8-year-old European X Japanese hybrid cultivar called ‘Colossal’ that has never been pruned or thinned since planting. You should be able to see the difficulties one will have training this relatively older tree, that since its planting, became stunted and dwarfed due to the odd branching. This tree will need to be treated special if it is to become part of the productive orchard again.
Photo 6. Two orchards with trees approximately the same age, but managed differently. One orchard well pruned (better control), and the other (organic orchard) never pruned since planting.
Photo 7. A 15-year-old ‘Colossal’ chestnut tree that has never been pruned or trained. The older a tree becomes, the more difficult it will be to bring about a well-shaped, productive tree. The lose in yield after pruning will be severe for 1 to 3 years, but it will eventually produce expected levels of chestnuts again. The older a tree becomes before training the greater the chances of harming yields. The benefits of a well pruned tree can be seen in terms of care for the tree. It is difficult to weed and the weeds will compete for water and fertilizer. Harvesting will be difficult, by hand or by mechanical means. The low branches are simply always in the way.
What then, should your young trees look like? That depends on the goals set for your orchard and trees. Do you want your orchard to be free of branches for at least 5 feet or more? Some growers consider that important so they won’t bump their head when mowing or for future harvesting.
Keep in mind that after 3 to 5 years of training, you need to enhance your thinning skills that can be used to remove dead, broken, and weak branches. Then, selectively remove limbs from the perimeter of the canopy, especially those growing close together or beyond the desired canopy size. Also, remove branches with narrow angles of attachment. Branches should be taken back to their point of origin or to laterals that are at least one-third the diameter of the limb being removed. Trees vary in the amount of thinning they can tolerate without creating undesirable effects. An over thinned tree will respond by producing numerous sprouts and suckers. Sunscald can occur on trees with thin bark. Never remove more than 30 percent of the total foliage at one time.
In general, our suggestion would be to reduce those water robbing side branches; if not in the first year, then by the second or third. Get some height on the tree and support it by staking with a ten or twelve foot (2-3 feet in the ground) metal conduit post and allow the tree to begin its branching at 5 or 6 feet. If you have a better plan that works, use it and share it with us!
In Australia, they graft five or 6 scions onto a cut trunk and then allow the scion to grow into a vase-shaped form (Photos 8, 9, and 10). This is not done with cabling, but exclusively by pruning.
Photo 8. A grafted chestnut tree in an Australian chestnut orchard. The scion was grafted to the older rootstock with a bark graft technique, allowing the buds to grow and then trained to give a vase shape (Photo 9) with a large branch coming out of the top. These grafts are the source of all the branches. All go up and out, and one is pruned to grow up. This form allows the sun to shine on all aspects of the perimeter.
Photo 9. A vase with a “snorkel” coming out the top of the tree. All of these branches came from the scion wood.
Photo 10. After the tree fills out, the shape is still present, a vase with a snorkel.