Choosing the growing form for an apple tree isn’t easy, considering that the selection depends on several factors such as rootstock vigor, variety, soil fertility, mechanization capabilities, plot size, labor availability, and more.
Since the onset of intensive production, apple orchards have become denser, with shorter trees that bear fruit more quickly, resulting in higher quality produce. The demand for denser planting has led to the use of dwarfing rootstocks and the adoption of new growing forms. Today, two predominant growing forms are found in intensive apple orchards: slender spindle and bush (stoolbed). We’ll help you make your choice of apple growing form easier with a detailed description of each option.
Spindle
It represents the standard growing form for apples. This form consists of a central leader and primary branches that also serve as fruiting wood, or shorter primary branches that bear the fruiting wood themselves. Therefore, this growing form has a central leader as its skeleton, while the semi-scaffold branches support the fruiting wood and the surrounding branches directly on the central leader. The slender spindle provides significant advantages in apple production by reducing manual labor in all orchard operations. Apples grown in a slender spindle form are typically trained to a maximum height of 2.2 to 2.5 meters. This height allows for easier management (minimal pruning, ground-level harvest, simpler and more efficient protection), and harvest.
Apart from easier maintenance, the advantage of this growing form is that it enables good yields and high fruit quality due to ideal light conditions, resulting in more pronounced coloration, uniform ripening, and maturity. Additionally, the nutrient balance is very good. Slim spindle ensures quick entry into fruiting, high efficiency, and fast financial returns.
In the first year of forming a slim spindle, the central leader is pruned to 80 cm height to promote the growth of lateral shoots. From these shoots, 5 to 7 well-developed ones are selected and evenly spaced about 20 cm apart along the central leader, arranged spirally. Afterward, flower buds are removed. As the shoots grow to a length of 40 cm or more, they need to be bent at a 45° angle. This training can continue until June.
In the second year, the tree needs to be tied to a support structure. If the central leader hasn’t strengthened adequately, it should be pruned back to the first strong shoot that will take over as the leader. The bent one-year-old branches should not be touched or pruned. During the growing season, any shoots that compete with the central leader are either pinched back or removed.
In the third year, the branches that bore fruit in the second year are removed, and the one-year-old shoots need to be thinned out. As extensions of the main branches, one-year-old shoots should be retained. Two-year-old fruit-bearing wood on the main branches needs to be pruned back to an optimal number of buds, depending on the branch’s position on the tree, the thickness of the fruit-bearing branch, and the overall vigor of the tree. On less developed fruit-bearing branches, it’s sufficient to leave 1 to 2 buds, while on well-developed branches in the lower part of the tree, you can leave 5 to 6 buds.
In the fourth year, first, it’s necessary to prune the central leader to the desired height of growth. After that, all upright shoots need to be removed, while the lateral, more horizontal shoots are left to maintain the tree at the desired height. Further proper pruning helps maintain the slender spindle training system, ensuring a good branch and canopy arrangement. It’s beneficial to supplement the main pruning with summer pruning during the growing season to increase canopy ventilation and enhance fruit coloring.
Spindle bush
This training system is also common for apples grown on moderately vigorous rootstocks and planted in close spacing. The basic form of the slender spindle consists of a central leader and spirally arranged branches that further branch out, depending on the type of fruit, into second, third, and fourth-order branches. From the base to the top of the canopy, the length of the primary branches gradually decreases, resulting in a well-shaped slender spindle that resembles a cone.
In the first year, unbranched one-year-old seedlings are shortened to a height of 80 cm in the spring before the growth of vegetation, while in the case of branched seedlings, the conductor is shortened to 50 to 70 cm above the highest premature shoot. If the conductor is shorter than the mentioned height, it is not shortened. Premature breakouts are also not shortened. In the phenophase of bud swelling, i.e. when the shoots grow 10 to 15 cm, it is necessary to isolate the tip of the conductor and each of the premature shoots. On premature shoots, only those saplings that grow sideways are left, weaker lush saplings that have a downward growth direction and one sapling at the top that will serve as an extension. In this way, the basic branch takes the shape of a “fishbone”. If one or more sharp shoots appear, it is necessary to remove them or pinch them sharply. The conductor should be tied to the support, and the other shoots should be wrapped if necessary. However, swaddling can be postponed until the saplings reach a length of about 30 cm.
In the second year, it is necessary to re-insulate the ends of the conductor and all side shoots. If the conductor has grown more than 80 to 90 cm, it must be shortened to 70 to 80 cm. In the phenophase of bud swelling, 1 to 2 buds are left at the top of the shoot, while the others in a length of 20 cm are removed by hand. All openings on the conductor at an angle of 45 to 65° should be bent at an angle of 90° in relation to the conductor. The distance between these shoots must not be less than 25 cm. Second-order branching occurs on the basic branches, and they must be arranged according to the “fishbone” principle. Some fruit trees can bear fruit already in the second year, so if too many fruits are set, they should be thinned out as soon as possible. In the third year, the formation of the spindly bush is mostly completed. In the period of rest, pruning is carried out only to repair the mistakes made in the second year and to thin out the excess reproductive shoots. The length of the branches from the base to the top is gradually shortened to reduce shading, and the final height of the fruit tree should not exceed 2.5 m. The top of the fruit tree is maintained by bending the conductor or is reduced to a lower, moderately lush shoot or branch.
