I have a Japanese Lilac in my back yard. It’s about 6 feet tall, with only 4 slim (4 inches around?) trunks on it – it’s not a large tree. It has grown askew due to reaching for sunlight. The trees that caused the lilac to grow this way have since been removed, and so I would like to prune off the unwieldy growth. I have heard of a ‘rejuvenation prune,’ best done when the plant is dormant. I have heard that the tree can be ‘taken down’ to its base, without killing it. Is this true? Due to this winter’s wacky temperatures, is it too late in the season this year? Any advice?
The Japanese Lilac Tree (Syringa reticulata ‘Ivory Silk’) is a wonderful tree introduced by Sheridan Nurseries in 1973. It is a compact tree hardy to Zone 3 and usually flowers in June. It has an oval or pyramidal form when young but spreads to a rounded shape as it grows older. This is a very large shrub or small tree, reaching a height of about 20 to 30 feet with a 15-foot-spread.
Syringa reticulata is frequently used as a residential street tree since it is tolerant of urban conditions, growing in poor, clay or alkaline soil. The flowers are most showy and prolific when the tree is located in full sun with good drainage. Plants in partial shade can be infected with powdery mildew, which can cause some defoliation.
Pruning is a means of manipulating a plant’s growth, shape and flower productivity by cutting and training it to achieve what you want.
Rejuvenation pruning is a technique that is usually performed on untidy overgrown shrubs. This technique involves severe cutting back of the shrub to a height of 10-25 cm from the ground. This pruning technique is usually performed in the spring before new growth begins.
Pruning of deciduous trees should begin by the removal of dead, diseased and broken branches. Your next step is to remove one-fourth to one-third of your tree’s largest stems using a pair of pruning shears or loppers. This step can be performed annually while the tree is dormant, before new growth begins to appear. Prune away all but 6 to 12 major stems, spaced so that they don’t rub against one another.
To control the height of your lilac tree, the branches should be trimmed to roughly one foot below the desired height in spring, right after the tree finishes flowering for the year. When trimming a branch, cut it back to 1/4 inch above a bud, or swollen section of the branch or stem so that you do not remove next years flowers. If possible, deadhead spent blossoms to encourage additional growth the following year.
It is also important to remember to fertilize your tree yearly with compost, composted manure, or a balanced chemical fertilizer and to ensure that the soil pH is close to neutral, which lilacs prefer. These amendments and some good mulch will help to stimulate vigorous new growth and better flowering in years to come.