Answer: While it is true that some lilacs can take several years to come into bloom, five does seem like a long time. The typical reasons for lack of bloom are pruning at the wrong time and lack of sunlight. A lilac would ideally have full sun all day long, but needs at least a half day of direct full sun to bloom at all well. Lilacs are not terribly demanding in terms of fertility, but you could try giving it a generous application of compost and/or well rotted manure late this fall and again in early and late spring and see if that makes any difference. You could also use a complete granular fertilizer such as 10-10-10 according to the label instructions. The blooming wood for next spring has already developed, so you might not see much difference until the following year. Finally, you might want to run some soil tests and make any necessary adjustments to bring the soil pH near neutral. The tests would also tell you if there is any nutrient severely lacking.
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