Answer: It's odd for the leaves to turn white, unless the white was a powdery coating on the surface of the leaves. If this is the case, your lilac had the symptoms of a fungal diesease called powdery mildew. This is common, especially late in the season when daytime temperatures are high and nights are cool. Since lilacs drop their leaves anyway, the best course of action is simply to rake the leaves up and dispose of them. If the leaves truly lost their color and there was no powdery mildew, it indicates your soil is in poor shape. Lilacs like a neutral to slightly acidic soil. If it is highly alkaline, nutrients will be tied up in the soil and unavailable to the plant roots. I would fertilize with an acidified fertilizer (one manufactured for azaleas and rhododendrons) and top dress the soil with some peat moss. As for flowering, some lilacs take 6-8 years to become established before they are ready to flower. But once flowering beings, look out! They will bloom their little heads off. Be sure your lilac is getting at least 6 hours of direct sunlight each day, water regularly during the growing season, and feed this spring with an acidified fertilizer (in amounts as listed on the label). With a little patience and a little care, your lilac will grow healthy and happy.
Best wishes with your landscape!
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