I finally realized that it was cutworms that were eating all of my newly planted begonias and hostas. I've managed to pick off a few remaining worms, but I'm guessing that their lifecycle has moved on, because I'm not seeing any more new damage.

I've already replaced one of the hostas, because it was just too tacky to be by the front door, but what to do about the rest? The begonias are looking pretty chewed and tattered.

I sprinkled the beds with Osmocote Plus at planting time. Would a watering or two with Miracle Grow help the foliage recover? Should I just be patient and wait for the plants to replace the leaves? Pull all of the worst begonias and just replace them?