It’s not their place and in midsummer they’re shutting down for the year. Give them a break and plant them where it is cool and damp.
There’s a basic misunderstanding going on in Vernon, where I live, which says that birches grow in soil and need water to survive. This thinking is based on a model of growth which sees plants as conduits evaporating off water and drawing water from the soil to replace it, dragging minerals along. Maybe so, but the speed at which it takes place is going to take its toll and age the leaves prematurely. That’s where a second misunderstanding is operative, the one that analyzes trees, sets their base state as a stem, which has leaves that open and fall, and that’s that. Thing is, the primary system is that of the leaf; the rest is secondary. Water flowing through the trunk is all fine and good, but it’s leaf health that matters.
Summer, in other words, is not a time of year but a rate of metabolic activity. It can pass quickly in dry hot air or slowly in cool wet air. It’s not that birches need soil and water. They need the proper sky. We might set the roots of the trunk in the soil, and call that “planting”, but we are really setting this sky creature in the air, or at least in a space between water and air. Wet soil doesn’t cut it, not because it’s the wrong soil but because it’s the wrong air. Let’s start planting our sisters in the correct sky.
Lilac, by the way, agrees. This is the sky for grass. Please plant that. It responds to it intimately, matching its maturity to dryness of air.