Answer: Lilacs are very forgiving about soil types, so is spirea. Itea however would probably prefer a moister soil than most sandy areas provide.
To troubleshoot the lilacs, start by reviewing the planting and watering procedures. Planting would be to prepare a large hole, set the plant at the same depth it grew before, water well to settle the soil. Use a layer of natural mulch several inches thick over the root area but not touching the stems.
Watering would be done to maintain an evenly moist soil but not a sopping wet soil. A periodic slow deep soaking is preferable to a daily light sprinkling. Use your finger to check the soil about an inch down and see if you need to water. After watering, dig down and see how far the water actually penetrated -- this can surprise you!
The soil should be kept moist all the way through fall until the soil freezes. This is important for winter survival. Although lilacs are actually tolerant of a dry soil, new plants must be watered regularly and then continuing for the next few years during dry periods until they become established.
Sometimes plants fail to root in to the native soil. There are many reasons why this can happen, but a common one is that the plant started out with encircling roots and they have continued to grow in that circle underground. To avoid this, look for plants that are not potbound or slice the roots or untangle them so they can grow outward. Another reason why this can happen is that watering is insufficient since roots will not grow into dry soil.
Finally, timing is important. The best times to plant are very early spring and again in the fall. Planting in mid summer is extremely stressful to plants and sometimes they can't recover from it.
ometimes, too, a plant will die for no clear reason. Since you had three die, though, there is probably an explanation. I hope this helps you troubleshoot, you might also want to consult with the nursery where you purchased the plants and also with your county extension to see if they have any suggestions.
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