Answer: The absolutely best times to plant new trees and shrubs is in the spring or fall, when temperatures are cool and rainfall abundant. Both will help the plants get their roots established before the heat of summer. If you plant in summer, plants will be stressed. They are trying to react to the summer sunshine and grow, but their roots aren't well established so the tops of the plants wilt. As soon as the roots are firmly established, your weigelas will perk up. Expect them to lose some leaves, and to look otherwise puny for a while. They will perk up eventually. In the meantime, water deeply once or twice a week, depending upon soil type and weather. If it's really hot and you have sandy soil, water twice a week; if you have clayey soil, water once a week.
Give your new plants a little more time and they should be just fine.
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