Apples and Peaches Summer Pruning TipsApples and Peaches Summer Pruning Tips
Rising costs have forced tree fruit growers to turn to more intensive planting systems to increase production per acre and per man-hour. As a consequence, tree crowding with a loss of productivity and fruit quality has occurred in some plantings. Traditional dormant pruning restricts root growth and reduces tree trunk enlargement, while it stimulates growth near the cuts. Such growth can worsen tree crowding and reduce light penetration. Fruit growers are therefore turning to summer pruning as a means of controlling growth. Summer pruning also offers a way to balance the workload by reducing the time spent on dormant pruning.
Pruning fruit trees during the summer has been of interest for well over 100 years. A few researchers in this country evaluated summer pruning between 1900 and 1920, concluding that responses were too variable to recommend its widespread adoption. Little was said or written about summer pruning in the United States between 1930 and 1975, when further research was begun in Virginia and Ohio. Since 1975, research has focused on the effects of summer pruning on apples and peaches. Misunderstandings about summer pruning have arisen and should be cleared up.
First, what is summer pruning? It is removing any vegetative growth when there are leaves or flowers on the tree. This includes desuckering the interior of trees, selecting scaffolds on young trees, tipping terminal growth, summer topping of peaches, and dormant-style pruning conducted during the growing season. With all pruning, be it dormant or summer, the ultimate effect is to control tree size.
Effects on growth
Probably the most mistaken idea is that summer pruning restricts growth more than winter pruning. Work in Virginia and Ohio on apples and in New Jersey on peaches has shown that summer pruning causes more vigorous vegetative growth the following year than traditional dormant pruning. Summer pruning does restrict increases in trunk enlargement, branch diameter, and root growth. However, tree crowding in intensive plantings is the result of shoot growth, and summer pruning does not suppress shoot growth as much as dormant pruning.
In assessing tree response to summer pruning, it is important to compare that response with the effects of comparable dormant pruning. For example, at the growing season’s end, a tree pruned in summer will obviously look much different from a dormant-pruned tree. After comparable dormant pruning, however, both trees look very similar.
The later you summer prune the less likely the chance of regrowth during the season of pruning. Pruning in mid- to late August can be beneficial to open the canopy up and to allow better sunlight penetration for enhanced color development of fruit.
Effects on flowering and fruiting
Research conducted on the effect of summer pruning on flowering and fruiting has had mixed results. In studies on apple trees pruned in late July or August, no increase in flowering took place the following year. Summer pruning is done earlier, in June or early July was shown to increase flowering in apples. Pruning Redhaven peaches on July 1 or August 1 reduced the number of flower buds proportional to the length of shoots removed; however, the August 1 pruning increased the number of flower buds per node.
In peaches, summer topping was shown to reduce the cold hardiness of flower buds on two out of four sampling dates. The flowering of summer-topped Sunqueen peach trees also appeared advanced, compared to that of dormant-pruned trees.
Effects on overall yield have been variable. In the Virginia apple studies, total fruit weight and numbers per tree did not consistently increase. In Ohio, fruit yield per tree was reduced, but yield per canopy volume was unaffected. Sunqueen peaches mechanically topped over a two-year period had a yield 9 percent lower than yields of dormant-pruned or normal summer-pruned trees. Overall, in individual cases, responses to flowering and fruiting probably depend on variety, timing, and severity of pruning.
Effects on fruit quality
The influence of summer pruning on fruit quality depends on variety and overall tree vigor. Summer pruning has been shown to increase fruit color, especially in crowded plantings where light levels are low. Severely summer-pruned trees tend to produce smaller fruit and lower soluble solids when pruning is done earlier in the season. On the favorable side, summer pruning tends to reduce bitter pit and enhance color in apples. Flesh firmness of Loring peaches was increased by summer topping. Summer de-suckering of peaches has been shown to be beneficial in improving fruit color without the side effects on fruit size. Desuckering consists of removing only the large vigorous upright shoots in the center of the tree.
Dormant-type pruning of apples even done in the summer may not lower overall pruning costs, but it does allow a better distribution of the labor force. Summer pruning offers the grower the option of maintaining a constant number of employees by shifting some of the winter workload to the summer. In mature peach trees, summer topping can save a grower 20 to 25 percent in pruning costs, although there may be a loss in yield after topping.
Summer pruning is a useful tool in fruit production, with certain limitations. It should never be viewed as the sole method of pruning. The best practice is to combine selective summer pruning with yearly dormant pruning. Summer pruning can help improve fruit color, alter fruit quality, train trees, and allow a better distribution of labor.
Before embarking on a program of summer pruning, growers must know what effect they wish to achieve. The earlier in the season summer pruning is completed, the greater the flowering and vegetative regrowth. Conversely, the later in the season summer pruning is done, the less it will affect flowering and the less regrowth there will be. Late-season pruning enhances fruit color but can reduce soluble solids and final fruit size.