Homegrown: Lilac bushes
For the past 2 years our lilac bushes have failed to bloom. Last year not even a bud. This year a few of the bushes got buds and only two little flowers opened up. I would like some blossoms next year. What can I do??
— Thanks, Terry
It seemed to be a bad year for lilacs this year; I know mine weren’t as showy as they usually are. We often see this—where a particular plant sort of takes a break. It’s often related to weather and how the plant performed last year. Obviously, nothing to do about that and I expect a much better flower show in 2012.
Now, having said this, there may be other things going on with your plants that would explain this lack of flower. One common reason for poor bloom is that the plant is not happy and under stress for one reason or another. You might double check the basic care the plant’s receiving, especially water. Lilacs are pretty sensitive to over watering, especially in our heavy clay soils. Do a little digging down and make sure that first, the soil is being soaked deeply when it is watered but then allowed to dry slightly before it’s watered again.
A second reason for a lack of bloom is that the plant is old and tired and in need of renovating. I often see old plants that consist of 10 or 20 large thick canes that are topped with an umbrella-like fringe of foliage at the top that blooms sparsely (if at all). This plant is badly in need of renovating. Like us, plants tend to lose their vigor as they grow older. However, unlike us, we can replace that old tired growth with vigorous new growth that will fill the plant out and bloom better.
The best way to prune suckering type shrubs like lilac is to rotate out old, worn-out canes by cutting them off near the ground so that younger more vigorous canes can grow up to take their place. Any cane with a diameter of an inch or more would be a candidate for removal. Use a pruning saw to cut them off as close to the ground as you can get. Young sprouts will grow up to fill the space and give your plant a lusher, more compact look with more flowers.
Now, I’m not advocating leveling the entire plant in one fell swoop! Removing this much growth at once is very stressful to the plant and can even result in killing the plant. This process should be done gradually, over a period of three or four years.
If this is something you may need to do, I think the best time to do it is in March. The more I see, the more I think pruning spring flowering shrubs like lilac, forsythia and snowball early is better than doing it right after they bloom which has been the standard recommendation. You lose some bloom that year, but the plants seem to recover better and fill out much more quickly.
The third reason for lack of flower is improper pruning. People sometimes try to control the size of the plant by pruning from the top down. The thing to understand is that lilacs (and the other spring flowering shrubs) set their flower buds the prior year. So any pruning in the summer removes those buds. Some of them, like forsythia, have flower buds up and down the stem, so if you shear them back, you still have some flowers. However, lilacs only set flower buds at the tip of the stem so you’re removing the flowers with any little shearing.
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