A little more direct sun is probably the reason you have brown leaves on your astilbe. Leaf burn is very common with astilbes that are getting too much sun and not enough water. You could consider moving the plant closer to the unaffected astilbe. If that isn’t possible, the affected astilbe will definitely need more water, not less. Surrounding both plants with a hardwood mulch, if you haven’t already, will help keep the roots cool and moist. You can remove the burned leaves, the astilbe should sprout new growth from the base.
The sun is shining, the birds are chirping and most importantly the snow appears to be gone. As spring approaches, the first things you might notice are the lawns turning green and plants starting to peak through the soil. It is very important not to get in a hurry when working on your lawns, you want to make sure it’s not too wet and the soil temperatures are right for the best performance.