When To Prune Plants. Plants that bloom in summer, such as potentilla and crape myrtle, produce their flowers on new growth from the current season. Spring is a great time to plant most trees and shrubs, but pruning in this season isn’t for every plant.
Prune forsythia, rhododendron, and lilacs for shaping or size control after flowering. Knowing how to prune a plant is about becoming familiar with your plants and showing patience. You can cut back the entire plant to 6 to 12 inches of growth (basically starting over), or you.