On two of my plants, a zinnia and a snapdragon, I've noticed that the dirt is separating from the edge of the pot, as if it is shrinking. I used potting soil and have been watering properly. What causes this?
Potted Plant Problem
Certified GKH Gardening Expert
This can happen if the sides of the pot heat up, causing the potting soil to dry and shrink away from the sides of the pot.
There is also the possibility that the plant is getting too dry between waterings, causing the peat in your potting soil to dry up and shrink from the sides of the pot.
This article explains the above and how you can remedy it: