Notes on Pruning Chestnuts
Pruning is a necessary practice to optimize chestnut productivity.
Like most tree crops, chestnuts require significant sunlight in the canopy to bear fruit, with research showing that at least 35% solar radiation is needed to produce fruit (Hall, 2000)— more than many other fruit trees. Though pruning styles differ throughout the world, the strategies of an individual pruning program will depend on contextual factors such as production goals, tree density, species growth habit, farm machinery, and climate.
Below we’ve provided some basics on pruning and chestnut-specific best practices.
Global Perspectives:
China: High-density orchards often use open-center systems, keeping trees short to maximize light penetration and ease of harvest (Becaro et al, 2018)
United States: Central leader systems, where trees are trained upward, are the norm. MSU Extension provides an excellent primer on central leader pruning.
Japan: Researcher Hitosho Akari has demonstrated that elliptical-shaped trees with as few as two scaffolding branches can be highly productive (Hall 2000), maximizing sunlight in the canopy.
Before you Get Started:
Establish Goals. Goals for a pruning program may include pruning for structure, health, & nut production, but will evolve as trees mature
Tools. At minimum, pruning shears and a hand-saw are required. Sharpness is key to effective pruning; sanitizing tools between trees is recommended.
Basics. Understanding types of pruning cuts, tree biology as it relates to pruning, and best practices helps you locate cuts appropriately.
General Guidelines
Pruning should be corrective, and never an end in itself. Never remove more than 30% of a tree’s foliage during any one pruning event.
Trees generally can only heal 3/4 inch per cut in a single growing season, so avoid pruning branches exceeding 2 inches in diameter.
During branch removal, cut at a 45° angle just outside the collar — i.e. the “branch protection zone” — to ensure optimal healing.
Prune while trees are dormant to avoid disease transmission and support healing.
For reference, Chestnuts break dormancy around 177 GDD (Growing Degree Days, which can be calculated for your region here).
Oak Wilt: Aim to prune before picnic beetle activity, as these insects transmit oak wilt. Beetle activity begins around 122 GDD - 392 GDD for the two primary vectoring species (Jagemann et al 2018).
Chesnut Blight: Chestnut blight is also transmitted by wounding. Avoid wounding if there was rainfall the week prior if possible, as propagule loads will be significantly higher 1 week following a rain event. Wounds are most susceptible for 1-2 days after pruning.
Remove the following unwanted growth: suckers & water sprouts; branches with bark inclusions; crossing or close branches; branches with suboptimal crotch angles (60-70 degrees is ideal); and dead, diseased or broken branches.
Fruiting wood must be carefully managed to sustain productivity:
Mixed Buds: Chestnut fruit grows on the current season’s shoots originating from the previous year’s growth. Mixed buds develop in late summer above maturing burrs.
Thinning for Light: Thinning branches to allow sunlight penetration ensures the development of new fruiting wood (Vossen, 2000).
Early Structural Pruning
During the early years, chestnuts undergo structural pruning to establish a strong framework:
Central Leader Training: A single dominant leader is encouraged by removing competing branches. If leaders compete, a subordination cut (a type of reduction cut) can be applied to weaken the secondary leader.
Permanent Scaffold Selection: Over time, 2-4 strong scaffolding branches should be selected. These branches should not exceed 50% of the central leader's diameter. Reduction cuts can manage their growth if necessary.
Temporary Laterals: Some temporary lateral branches can remain during early growth but should eventually be pruned out as the permanent framework develops.
Open-Center Systems vs Central Leader Structure: If an open-center system is preferred, the central leader is removed. For central leader systems, multiple tiers of scaffolds can be created, spaced 24-36 inches apart. Within each tier, laterals should be spaced 6-12 inches vertically.
Height and Clearance Considerations
Machinery Clearance: The lowest branches should be high enough to accommodate machinery. Red Fern Farm recommends 8 feet of clearance.
Tree Height: Dr. Hirtosho Akari suggests keeping trees small, with a maximum tree height of 13.1 feet to ensure manageable maintenance and harvesting (Hall, 2000), but many growers in the US opt not to restrict height.
While you Prune
Scouting: This can be a good time to scout for cankers and galls, which are more visible in the canopy after leaves have fallen.
Pruning and Tree Shelters
Tree shelters can reduce early pruning needs, as branches inside the tubes often self-prune. However, sheltered trees may develop weaker trunks and root systems, and tubes can occasionally girdle or damage the trunk.
