Answer: Watering a lilac twice a day is a bit too much. One deep soaking per week - twice if it's really hot - should be all your lilac needs. In general, lilac's like well draining soil and full sunshine. What I would suggest is waiting until this fall when lilac's normally lose their leaves, then digging the plant up, amending the soil with compost or aged manure, then replanting it. Make a watering well or basin beneath the plant and flood the basin, allow to drain, then flood it a second time. Do this once each week during the growing season (unless there's at least an inch of rain per week). Amending the soil will help it drain quickly, yet hold just the right amount of moisture. A watering basin beneath the plant will concentrate the moisture directly over the root system and allow it to trickle down and wet the entire root mass. Both these things should make your lilac happy.
Best wishes with your lilac!
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