Answer: Lilacs are not usually too difficult to grow in average soil and a sunny location. Maybe you have been too kind to them! Usually the hardest part of establishing a new plant is watering it correctly. The soil needs to be kept moist but not soggy or sopping wet, and the best way to water is to water deeply when the soil has begun to dry out -- this means about once a week and not every day. The only way to tell when to water is to test the soil with your finger. The next step is to keep the plant mulched with several inches of organic mulch to help keep the soil cool and moist. A lilac would not ordinarily need to be staked, and pruning would only be needed after several years. Fertilizing would be accomplished by a top dressing of compost and/or a complete fertilizer in granular form being applied according to the label instructions at planting and in early spring.
If you think your planting technique and care have been correct, then I would suspect a soil problem. This could be something obvious like poor drainage (meaning the soil is always sopping wet ot it floods when it rains) or it could be something hidden such as the top soil was imported when your house was built and it is of an unusual pH or has an imbalance of some sort. If you think this might be the case, you might run some soil tests and consult with your county extension (732-1470) about it.
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