Why won't lilac tree bloom?

Answer 1

It could be an excess of nitrogen which promotes leaf growth over flowers. Possibly the soil is too rich or lacking in the element phosphorus. Most garden centers keep products to restore such an imbalance so the plants don't then get phosphorus burn.

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sounds like lack of sunlight to me

Answer 2

Blooming requires a lot of energy from any plant, shrub, or tree. They need nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, boron, chlorine, copper, iron, manganese, molybdenum, and zinc. Nitrogen is the most important, followed by phosphorus and potassium. All growing things need nitrogen to both grow and to decay back into the soil. Perhaps fertilizer or richer soil amendment needs to be added, although lilac trees prefer neutral soil when it comes to acidity. Other factors are not enough sun, powder mildewing, poor drainage, and over-pruning. Buds for the following blooming season begin in early to mid-summer and need to over-winter, so it's important that they not be disturbed or damaged by the aforementioned conditions.

Answer 3

Lilac bushes that do not get enough sun will not flower. Also if you prune a lilac in winter or spring, you are cutting the flowers off.