Afraid to prune perennials? With care, they’ll thank you for a gentle touch up

Pinching, cutting back and pruning are not terms we usually associate with the perennial garden. However, these practices can benefit many plants, as well as help to improve flowering, growth and general appearance throughout the garden. The terms might sound confusing and unnerving, but these tips make the process simple to implement with stunning results.

Pruning perennials revitalizes the plants and encourages a flush of new growth, which promotes bud formation for new flowers. This helps to control height by creating a fuller plant that is less likely to fall over.

Spring flowering perennials

Many spring flowering perennials, such as creeping phlox and dianthus, are low growing or form a dense mat of foliage. Once flowering is finished, remove about a third of the old growth with grass shears or pruners.

Trimming off the old top growth removes the faded flowers and encourages new growth, which may result in sporadic flowering. Pruning can help prevent tall leggy growth, which will flop or create open spots and reveal a less attractive area. It also creates a shorter, more compact plant that is denser and more attractive.

Nepeta, or catmint, which flowers throughout the summer and fall, responds well to this removal of the old flowering growth.

Summer flowering perennials

Perennials that flower in early summer put on a flush of rapid spring growth and bloom in late May and June. Many of these plants produce a mound of foliage that terminate in a cluster of flowers. They can benefit from pruning out old flower stocks.

This process of removing spent flower stocks is referred to as deadheading. Deadheading removes the flower scape at the point of connection to the plant, often at the base. Examples of this would be iris and daylily. Other perennials are pruned back only to a lower side branch or bud. Plants that produce multiple flowers up and down the stem will benefit from removal of faded flowers in several ways.

Deadheading keeps the plants cleaner and reduces seed formation, which will help the plant put its energy into generating additional flower buds. This depends on the flowering habit. One-time flowering plants like peony, daylily, iris or Baptisia (false or wild indigo) will not result in additional flowering. In these cases, deadheading will only serve to keep the garden tidy.

Repeat flowering perennials like Shasta daisies, Achillea (yarrows), and Echinacea (purple coneflowers) will continue to produce flowers throughout the season with timely deadheading. How often you deadhead depends on you. For highly maintained gardens, weekly is a good schedule.

Late summer and fall flowering perennials

Late season flowering plants often grow tall, then they can fall and droop and become unruly and less attractive.

When you cut back by half or more to control growth, and prune or cut out the terminal bud, you stimulate increased growth of side shoots or stems. The result is a fuller, more compact plant with stronger stems that are less likely to collapse and added shoots with flower buds. This practice is most common on fall blooming chrysanthemums. It can also be done to aster, sedum, eupatorium (Joe-Pye weeds), hibiscus and solidago (goldenrods).

The process can be accomplished by shearing the plant or cutting each individual stem just above a leaf node. Within a few weeks new growth will emerge and mask the sheared look of the plant.

These procedures may be unnerving at first, but once you understand how your plants grow you will feel more confident. The result will be increased production of flowers and a pleasant, tidy garden setting.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Have a question for him or other university extension experts? Email them to garden.help@jocogov.org.

This story was originally published May 27, 2022 at 5:00 AM.