The Q&A Archives: Leggy Lilacs

Question: I want to use lilac bushes as a screen at the back of my property. Young lilac bushes have the dense appearance I am looking for, but I've noticed that older lilac bushes tend to get "leggy" and loose their leaves off the bottom half of the plant. Is there a special way that I can prune my young lilac bushes to prevent them from losing their bottom leaves? Should I just give up and start over with another plant?

Answer: Legginess can be caused by a lack of sunlight. Make sure your lilacs are in full sun and not shaded by surrounding trees. Some die back of older leaves is normal, as the plant's energy will go towards newer growth. Shrubs grow outward from the tip of the branch. The plant produces growth-inhibiting hormones called auxins that it sends back down the branch to prevent other buds from growing. The purpose is to ensure that the plant?s energy supports the tip?s growth. This is called apical dominance. For shrubs, if you want dense branching you need to cut back the growing tips. This halts the production of the auxins and stimulates the development of lateral or side buds. However, you have to prune at the appropriate time so you don?t cut off wood that the shrub will flower on. As a general rule, summer blooming shrubs flower on new growth; spring bloomers flower on last year?s growth.

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