Detailed Explanation of the Key Points of Black Locust Shaping and Pruning Techniques

Black locust grows fast, has strong adaptability and fine timber quality, and is an excellent tree species for afforestation and roadside greening in our province. However, black locust has very strong sprouting ability; if not pruned, it will grow branches all over the tree, so dense that air cannot circulate, thereby affecting growth speed. According to observations, properly pruned black locust has an average annual growth of 72cm, while unpruned trees grow only 49cm; with continuous pruning, it reaches timber and forest maturity 3-5 years earlier than without pruning. To achieve this goal, attention must be paid to shaping and pruning.

Under natural growth conditions, black locust has strong branching ability and vigorous growth, often forming a broad ovate crown, but most trunks are low and have too many branches, forming "small old trees." Shaping means making the trunk straight and tall; starting from the first winter after planting or the second spring, side branches competing with the main trunk should be pruned away, until after 5-8 years the trunk height is above 6m, reaching the standard for civil timber.

Large black locust saplings used for landscaping are generally quite vigorous; first select a robust, upright 1-year-old branch at the top as the trunk extension leader, then cut off 1/3-1/2 of its tip. Weak branches should be heavily pruned (but not too heavily, otherwise strong branches will not easily grow below the cut). If there are small weak branches near the cut, some of them should be pruned away, and the side branches above should be cut back one by one so that none of their tips is higher than the trunk cut.

Pruning

The timing and amount of pruning should be determined according to the purpose of afforestation. For general afforestation, pruning should be carried out after the young forest canopy closes; for roadside greening and shelterbelt strips, in order to cultivate taller trunks and prevent excessive shading, proper pruning should be carried out within the first 3 years. The techniques of pruning are, first, thinning: for example, black locust less than 2 years old has a relatively low main trunk, so generally select vigorous, upright branches as the main trunk and thin out the rest according to circumstances; according to the crown-to-trunk ratio (3:1 for 2-3 years old; 1:1 for 4-6 years old; 2:3 for 8 years old), after pruning the trunk to a certain height, thin out the thick competing branches, water sprouts, upright branches in the upper crown, and some overly dense side branches, drooping branches and dead branches. Second, heading back: that is, in summer cut back and remove upright, vigorous side branches; according to the principle of suppressing the strong and retaining the weak, removing the upright and retaining the horizontal, heavily pruning the upper crown and lightly pruning and leaving the lower part longer, make medium cuts in stages, leaving small branches below the cut, and they must not be thinned from the base, so as to avoid wind breakage of the main shoot or weakened growth. For young trees whose main trunk was topped or cut back at ground level in winter or spring, when the vigorous branches sprouting at the cut grow to about 30cm, keep one upright, robust branch to train as the whole leader, and cut the rest back by about 1/3 of their length; this can be done 2-3 times in succession. For thick branches under the crown, cut them back year by year, preferably leaving 1-2 slender weak branches.

Pruning of sprouts

After pruning, vigorous growing branches on the main trunk or main side branches should be pinched or tipped; new buds and sprouts emerging at thinned branch sites at the base of the trunk and at the top of the main trunk that was topped in winter should all be cut off early. Pruning should be carried out in summer, preferably from early June to early July, which has the advantages of small wounds and fast healing, generally no longer sprouting large numbers of branches, and is beneficial to the growth of young trees. Pruning must not be too heavy, and should be close to the trunk without leaving stubs, so as to avoid forming knots. Tools used should be sharp, wounds should be smooth, and branches and trunks should not be split.