Answer: The most common reasons for lack of bloom on lilac are too little sun and pruning at the wrong time. Ideally this shrub should have full sun all day long, or a bare minimum of six hours including the hour of noon. With only four hours, I suspect you are right. The other possibility though, since you might get at least a few blooms in low light, is pruning. This shrub blooms on old wood that grew the year before, so limit pruning to late spring/early summer. Ordinarily, this would be right after the lilac blooms. I wish I could be more encouraging.
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