Blooming lilac bushes fill the air with a sweet, fragrant scent, and the flowers signal the start of the warm season. Sometimes, however, a lilac bush -- even one that thrived in previous years -- can fail to bloom, leaving you without a single flower. Unlike shy groundhogs, timid lilac blooms don't necessarily mean six more weeks of winter -- a number of factors can keep lilacs from flowering.
Lilac bushes, like most plants, love sunlight and need to bask in it to grow to their full potential. One of the big reasons lilac bushes fail to bloom is that they simply don't catch enough rays -- lilacs require at least six hours of full sun every day. Watch the bush for a day or two and make sure it isn't in an overly shady area. Trimming the older branches near the base of the bush helps sunlight to reach the plant's inner recesses.
Lilac bushes need to be settled before they start producing blooms. Young lilacs spend their first few years growing and developing and won't produce a single flower until they've reached the ripe old age of three to six years. Transplants also take up to three years to acclimate to new ground.
Healthy plants grow from healthy soil, and lilac bushes are no exception. However, you could be killing your blooms with kindness. Lilacs require very little fertilizer -- especially fertilizers with excessive nitrogen. Select a fertilizer that contains at least twice as much phosphorus as it does nitrogen and only use it once, in the early spring.
Another common bloom killer is the acidity level in the soil. Lilacs like soil pH levels between 6 and 7. Amend the soil to raise the pH if testing shows your lilac is sitting in acidic soil.
You reap what you sow. Improper lilac care in the summer can devastate blooms the following spring. Prune the bush within two or three weeks of the blooms dying. New buds start to form soon after old blooms wilt and fall away, and you're chopping off next year's buds if you want until midsummer or later to prune. Thirst is another major factor affecting lilac bushes in the summer. Lightly water the soil around the bush during droughts -- just enough to moisten the soil rather than leaving it sopping wet.
Lilac buds start to bloom in the early spring. A late freeze can kill blooms in their infancy. You could also be trying to grow the wrong type of lilac for your region -- Meyer lilacs respond better in areas with mild winters, and common lilacs like colder winters.