Check the roots
Over the course of the summer, repeated watering may alter the soil level or unmoor a few root balls (especially those of trailing plants, which get heavier as they grow longer). Carefully lift up foliage to see if any roots are exposed. If so, don’t try to push them back in; instead, cover them lightly with additional moist potting soil.
Cut your losses
If a plant in a mixed container is dead, cut it off at its base to give its healthier neighbours room to spread. Doing this, rather than digging it out, avoids disturbing the roots of nearby plants.
Bring in your B team
Sometimes it’s necessary to completely remove plants past their prime and insert new ones, especially if you plan to transform a summer container into one that will last through fall. In this case, carefully dig out the root ball with a narrow-bladed trowel. Try to slice—rather than tear—through entangled roots. Install new plants with fall interest, such as small chrysanthemums, asters and pansies. Then give the container a light feeding of transplanter solution, mixed at half strength.