Pruning

Many landscape problems can be avoided if plants are pruned correctly while in the nursery. Incorrect pruning practices or lack of pruning diminish the quality of landscape plants. Learn when and what to prune in order to grow premium field nursery stock.

The most important aspect of growing nursery stock during the first year is root establishment and development. Top form and shape are less important for small liners than root growth, and allowing the top to grow provides the energy to develop roots. Small nonirrigated liners often experience loss of leaders and secondary branch dieback, which will necessitate pruning later.

Pruning during the first year should be limited to (1) unbranched nursery line-out stock if it is too tall and weak to stand erect and if staking is impractical; (2) dead terminals that need to be pruned on single-stemmed trees, and a new leader established. If the leader is pruned or is dead, branching will occur during the first year on whips, and these may also require some heading back to keep vigorous shoots from growing too long; and (3) any vigorous lateral branches of newly transplanted liners may need to be pruned by mid-summer to avoid lateral branches out growing and suppressing the main leader of trees such as maples, ash, oaks, and flowering pears that are sold as straight single-stemmed trees.

Select a lateral bud or shoot as a new terminal if the terminal of a leader is dead or if it is cut back while the tree is still dormant. On pears, cherries, and crabapple, it is advisable to remove three to four buds below the selected terminal bud to prevent multiple leaders from forming. A bud clip placed next to the bud or masking tape wrapped around the bud can direct the growth upward without a crook forming (Figure 3). If the tree is opposite budded, the bud on the opposite side of the bud selected as the terminal must be removed. If a terminal is observed to be dead after shoot growth has occurred, a lateral shoot can be bent upward and attached to the portion of the dead terminal for support, and other competing shoots removed or headed back at a node approximately one-half the length of the shoot. The dead leader can be removed after the new terminal is firm enough to stand or during dormant-season pruning.

For misshaped seedling trees, often the best choice is to cut them off at the ground just before bud break the second season. This practice can result in high mortality in dogwoods, Japanese birches, and other plants with low vigor, so use this method selectively. After new shoots develop, the healthiest and straightest one should be selected and the others removed.

Any other pruning the first year should be confined to broken branches and large lateral branches which are out-of-scale with the main leader. Large lateral branches that are low on the main stem should be removed, and smaller low branches may be pruned back to two to three buds to help caliper development of the lower stem during late fall months. Remove these short branches during dormant winter pruning. If branched trees are planted, similar procedures may be required to reduce competition of lateral branches with the leader. By mid-summer, competing lateral branches may need to be pruned to approximately one-half their length by cutting to an outward facing bud.

For clumped or multi-stemmed trees such as river birch and crapemyrtle, no pruning is necessary during the first year; however all but three to five main stems should cut at ground level before the second growing season.

The species’ growth habits generally dictate pruning requirements during the second and third growing seasons. It is easiest to work with the natural growth habit of a species than to change the natural form. Medium to large shade trees such as oaks, ‘Bradford pear,’ or maples are usually pruned to maintain a single leader and well-spaced, wide-angled branches. Other trees such as many crabapple cultivars, flowering plums and cherries, and other small ornamental trees may be pruned to form three to five modified leaders with low, wide scaffold branches. These modified leaders should be spaced 4 to 6 inches apart on the main stem. The height at which the modified leaders are established is determined by the intended market.