It’s lilac season in the Lilac City and the air will soon be fragrant with their heady scent. Lilacs are perfect for our Inland Northwest gardens. They love our weather, don’t need a lot of pruning and aren’t usually bothered by many pests or diseases.
Lilacs need at least four to six hours of sunlight a day to grow well. Without it, they get leggy and do not bloom as profusely. They prefer well-drained soil and don’t need regular fertilization. Once established, they are fairly drought tolerant.
Lilacs do need space to look their best. Many can grow as tall as 15 feet and stretch ten feet across with time. Plants that have room to show off their natural form need less attention over time. If you have a small space, look for smaller growing plants like ‘Miss Kim’. Because mature plants cast dense shade, they can make it difficult to grow other plants under them. Depending on the variety, lilacs can bloom from late May well into June.
Why no bloom?
Young plants can take several years before they begin blooming. Other reasons for not blooming include getting too much shade or too much fertilizer.
Human error in pruning, however, is the major reason for poor bloom. The best time to prune a lilac is within ten days after it finishes blooming before the buds for next year’s blooms form. If the plant is pruned too late in the summer or too early the following spring the buds and the blooms are lost.
Rejuvenating overgrown lilacs
Overgrown plants can be rejuvenated with a heavy pruning program. Remove a third of the oldest wood from the plant each year over a three-year period. Take out the tallest stems with the fewest leaves and flowers first, cutting them close to the ground. The lilac naturally produces suckers that will replace the wood you remove. At the end of three years, you will have a brand new, vigorous plant.
Diseases and pests
Bacterial blight is a problem on some plants especially after hot, humid weather. Leaves will suddenly appear scorched on the edges and young shoots will blacken. Cut out damaged branches well below the damaged area.
Powdery mildew can affect the aesthetic look of the plant but won’t harm it. Plant resistant varieties of lilac or plant tall perennials in front of the lilacs to hide the mildew.
Insects, like oyster shell scale, aphids and leaf miners, can be a problem and can be dealt with using insecticidal soap.
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