You can do that you know by cutting them back at the right times.
Each time you cut them back, it takes about 2-3 weeks for them to rebloom if you foliar feed. When you cut them back early, it has a minimal effect, but cut them back in July you will see a speedier change in growth.
If you want plants to bloom in September for instance, cut them back late July. If they normally bloom in August, bump that up to a hard shearing at the end of June.
Here’s a trick designers use. Take a mature perennial and cut it back in stages. Leave the back of the plant to grow normally, but take the front-half of the plant and cut it back to half its size in late May or early June. Cutting time depends upon how fast the plant grows and what time during the season a plant will bloom.
Above the sage after it was cut a week ago, the gallery below when it was just cut. Click to see the penstemon and sage just cut. You can see how this method becomes easily a benefit to the garden. A few weeks later, the front portion will flower. No staking is required since the bulk of the plant has been cut back. They will not flop in the garden now as the growing front part will now support the back half.
The front of the plant that was cut will begin to bloom 2-3 weeks later than the back half. As the back half is finished, it can be deadheaded and be hidden by the blooming front half. The new bloom hides the back side’s declining foliage from view. It doubles bloom time and also reduces the number of plants you might add to cover spent foliage. See the gallery above as I cut both Salvia nemorosa and Penstemon digitalis ‘Husker’s Red’.
If you have a clashing color combination, this technique can be used to delay blooming of one or the other. It might resolve moving one of the plants.
Some perennials will have unattractive bare stems. When they lose the lower, yellow leaves, the flowers may be beautiful but the foliage detracts. By step cutting the front of a plant as mentioned above, you can create a layered effect to the plant, hiding what you would rather not see. This technique works especially good on one particular perennial or large drifts. Cut at intervals to spread out the bloom time for many more weeks.
I have used this technique on Monarda, Shasta Daisy, Veronica, Asters, Nepeta racemosa ‘Walker’s Low’, Hibiscus, Campanula grandiflora and Echinacea, among others. Try it. Nothing to lose and you might end up doing what the pros do to keep those gardens in continued bloom.
I hope you are enjoying some of the tricks of the trade. Coming up… Potting Up the Pretty Perennials.