In high-density systems excessive growth is discouraged, and instead of a large, strong framework, a weak-framed tree is desirable. To achieve these ends in a system such as tall spindle, very little pruning is done in early years.
Generally, cost of trees in the long run is a small part of production costs. The big expense is in the labor required for early training and pruning. This expense should decrease over time, but the higher the density, the greater the labor requirements. A good rule of thumb is: "The more intensive, the more expensive." Penn State has an on-line spreadsheetto help you determine the cost of materials needed for a support system.
For optimal production, it is necessary to make best use of the surface area of available land. Spacing that is too wide makes for inefficient planting, while spacing that is too narrow means that excessive labor will be needed to contain trees in their allotted spaces. Once a production system is worked out, spacing is determined by cultivar to be planted, rootstock, soil vigor, and slope.
Any given production system will be only as good as the grower's ability to manipulate the trees. The more intensive the system, the more growers or their workers must be familiar with how trees grow. There is less room for error in high-density production.
A high-density orchard requires greater management skills; it also requires that labor be spread over a longer time period. Pruning must be done in both winter and summer. Because tree size is smaller, production becomes more efficient. Brains and nimbleness replace the need for brute strength, allowing greater flexibility in the labor you can hire. High-density orchards also make it easier for fewer people to take care of more trees, but in a smaller area.
Common misconceptions clarified
- There is no perfect production system. You need to develop your own style and a production system that suits your abilities, growing conditions, and chosen cultivars.
- High density does not necessarily mean greater yields. It is very possible to achieve 1,000 bushels per acre on well-managed, standard trees. However, it takes more years to reach full production capacity with standard trees than with dwarf trees.
- Yields and dollar returns do not always occur more quickly in high-density production. Mismanaging a high-density system in the early years can delay fruiting and production. Since the purpose of high-density plantings is to have early production, anything that delays early production will delay returns.
Finally, do not pass judgment on a particular system without adjusting all the factors.
Too often, growers give up on a system because they have tried to handle it the way they handle all their other systems. Make allowances for different row spacings to accommodate smaller equipment.
Production Systems for Apples
As the Pennsylvania industry moves from conventional medium-density, freestanding orchards to high-density, supported orchards, many pruning and training modifications must be made. In the medium-density central leader system, portions of trees are cut back severely for several years to stimulate growth. Emphasis is placed on building a large, strong framework to support future crops.
Conversely, in high-density systems excessive growth is discouraged, and instead of a large, strong framework, a weak-framed tree is desirable. To achieve these ends in a system such as tall spindle or French axe, very little pruning is done in early years. The goal is to promote early fruiting, which itself will inhibit future growth. All high-density systems require a greater knowledge and understanding of plant growth and of how the tree will respond to cuts. In early years, more attention is paid to training and positioning limbs than to pruning them. As trees mature, most high-density systems will be more productive if trees are pruned in both winter and summer.
High-density systems also demand greater precision in spacing trees. Since trees are not meant to be vigorous, too wide a spacing is an uneconomical use of the land. Conversely, too narrow a spacing will necessitate more pruning, increasing vigor and reducing light and fruit quality. Below is a "cookbook recipe" on pruning and training the tall spindle apple system. This system is also described in a Penn State Extension video.
Tall spindle - a high density training system
This is a supported training system that depends on utilizing well-feathered (branched) trees that can produce a crop the year after planting and continue to increase fruiting in the immediate subsequent years. The tall spindle was developed as an offshoot of the slender spindle training system to take advantage of increased canopy volume by increasing tree height. To develop this training system, several components are important:
- plantings must utilize high densities (800 to 1,500 trees per acre)
- fully dwarfing rootstocks such as M.9, B.9, G.41, G.16 must be used
- nursery trees must have 10 to 15 feathers
- minimal pruning occurs at planting
- feathers are bent below horizontal after planting
- permanent scaffold branches are not be allowed to develop
- branches are renewed as they get too large. (for illustrations, please visit the extensive listing of tall spindle publications and videos from the University of Massachusetts.
- At planting: Plant highly feathered trees (10 to 15 feathers) at a spacing of 3 to 4 feet by 11 to 12 feet. Adjust graft union to 6 inches above soil level. Remove all feathers below 24 inches using a flush cut. Do not head the leader or the feathers. Remove any feathers that are larger than one-half the diameter of the leader.
- At 3 to 4 inches of growth: Rub off the second and third shoots below the new leader shoot to eliminate competitors to the leader shoot.
- May: Install a 3- to 4-wire tree support system that will allow the tree to be supported to 3 meters. Attach the trees to the support system with a permanent tree tie above the first tier of feathers, leaving a 2-inch-diameter loop to allow for trunk growth.
- Early June: Tie down each feather that is longer than 10 inches to a pendant position below horizontal.
- Dormant: Do not head leader or prune trees unless there are scaffolds that are more than half the diameter of the central axis.
- Make sure the leader is securely fastened to the support wires or conduit
- At 4 to 6 inches of growth: Pinch the lateral shoots in the top fourth of last year's leader growth, removing about 2 inches of growth (the terminal bud and 4 to 5 young leaves).
- Early June: Hand-thin the crop to single fruit 4 inches apart (target 15 to 20 fruit per tree if tree growth was good; otherwise, base crop load on tree trunk diameter and bearing habit according to the table below).
- Mid-June: Re-pinch all lateral shoots in the top fourth of last year's growth. Tie the developing leader to the support system with a permanent tie.
- Dormant: Do not head the leader. Remove all broken branches by heading back or renewal cut to a spur. Remove overly vigorous limbs that are more than two-thirds the diameter of the leader using a bevel cut.
- Late May: Chemically thin according to crop load, tree strength, and weather conditions, and then follow up with hand-thinning to the appropriate levels to ensure regular annual cropping and adequate fruit size (target 50 to 60 fruit per tree). See the table below to adjust crop load based on trunk diameter and cultivar.
- June: Tie the developing leader to the support system with a permanent tie.
- August: Lightly summer prune to encourage good light penetration and fruit color.
Number of fruit to leave on young bearing apple trees
|Trunk diameter (in.)||Annual bearing habit||Biennial bearing habit|
- Dormant: Do not head the leader. Remove overly vigorous limbs that are more than two-thirds the diameter of the leader using a bevel cut.
- Late May: Chemically thin and follow up with hand-thinning to the appropriate levels to ensure regular annual cropping and adequate fruit size (target 100 fruit per tree).
- June: Tie the developing leader to the support system with a permanent tie at the top of the pole.
- August: Lightly summer prune to encourage good light penetration and fruit color.
Mature tree pruning (fifth to twentieth leaf)
Dormant: Limit the tree height to 90 percent of cross-row spacing by cutting the leader back to a fruitful side branch. For example, if the cross-row spacing is 11 feet, then 11 x 0.9 = 9.9 or 10 feet. Annually, remove at least two limbs, including the lower-tier scaffolds that are more than two-thirds the diameter of the leader, using a bevel or Dutch cut. Columnarize the branches by removing any side branches that develop. Remove any limbs larger than 1 inch in diameter in the upper 2 feet of the tree. On varieties like Delicious, Gala, Golden Delicious, and McIntosh, if shoots start to taper down to smaller than pencil size in diameter, head them back to where they are pencil size, preferably to a slightly upright growing shoot or spur.
Source: Penn State Tree Fruit Production Guide