Answer: Yellowing leaves on birches this early in the year usually indicates stress of some sort. Excessively hot weather can cause the problem, as can too much or too little water, or over-fertilization. In the case of your birches, it might also be a reaction to being transplanted. If so, your trees will eventually adjust and begin growing well for you. All birches require a regular supply of moisture and nutrients. When you apply water, be sure to apply slowly so it has a chance to trickle down and wet the entire root mass. The frequency of water application depends upon weather and your soil type - sandy soil drains rapidly and needs to be watered more often than clayey soil. As a rule of thumb, we recommend one deep soaking once each week to help newly transplanted trees and shrubs become established.
I don't know if French drains are necessary - too much water excludes air from the soil and will drown the roots. At this point I'd continue to water regularly and give the birches time to adjust. The trees will probably replace the leaves they've already dropped. If not, they should leaf out well for you next spring.
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