How to Help Perennials Bloom Longer into Summer

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Enjoying the beauty of plants and flowers is the number one reason most of us love to garden, so it’s always fun to find new ways to help our plants look better and bloom longer. Over the years, I’ve picked up some tricks that can be used to help perennials bloom longer into summer. Here’s what I’ve learned.

salvia before and after cut back
A vigorous grower like a perennial salvia can be cut back all the way to the ground after its first round of blooms fade. New growth will emerge quickly, accompanied by a second flush of flowers. Photos: Adam Glas

Some plants respond well to a heavy cutback

While it may seem severe, there are many plants that benefit from a hard cutback after their initial flowering period finishes. A few plants that respond beautifully to this harsh treatment include perennial sages (Salvia nemorosa and cvs., Zones 5–9), catmints (Nepeta spp. and cvs., Zones 3–10), and spike speedwells (Veronica spicata spp. and and cvs., Zones 3–8). As the flowers fade, harden your heart and cut those lovely plants as far back or as close to the ground as possible to stimulate the formation of new foliage and flower buds. Often, as flowers are fading, these perennials will already be producing new growth from the roots, and a few weeks after the cutback you will be rewarded with a second flower display. Although the second show may be more subtle and less robust than the first, it is certainly worth the effort, and your compost pile will be thankful for the new addition of green material.

lavender plant before and after cut back
A lavender plant that is reduced by a third to a half after it blooms may flower again later in the season. Photo: Adam Glas
coreopsis before and after cut back
For this coreopsis, a cutback after the first blooms fade is exactly what the doctor ordered. Photos: Adam Glas

A more measured approach is sometimes better

In a previous article I discussed the Chelsea chop. This type of pruning involves cutting back the new foliage and stems of certain perennials before flowers emerge, encouraging the plants to form side shoots and produce more flower buds. While the Chelsea chop is usually done from late spring to early summer, this same method can be applied to perennials like tickseed (Coreopsis spp. and cvs., Zones 3–9) and lavender (Lavandula spp. and cvs., Zones 4–10) after they finish flowering. When you cut their foliage back by one-half to one-third, the plants will respond by pushing out a second round of flowers after the normal blooming period.

daylily with spent flowers and foliage removed versus left untouched
At the back of this bed, the daylily plants on the right have had spent flower scapes and foliage removed, while those on the left have been left untouched. The plants in the foreground were cut to the ground, but these vigorous growers will soon bounce right back. Photo: Adam Glas

When it comes to daylilies (Hemerocallis spp. and cvs., Zones 3–10), there are two options. The first approach is to remove spent flower scapes and any unsightly foliage as close to the ground as possible. The second is to cut all of the flower scapes and foliage back to the ground. Both methods are viable solutions to create a tidier appearance, and both will result in the growth of new foliage and often a modest second bloom.

betony before and after cut back
Although this betony is not likely to rebloom after its flowers are cut back, the foliage will look much better. Photos: Adam Glas

Many early season bloomers look nicer after a light haircut

Some harbingers of spring or early summer benefit from a trim to remove past-peak flowers. Although this group of perennials may not rebloom, their maturing blooms or seed heads may distract from their otherwise lovely foliage. This group includes dianthus (Dianthus spp. and cvs., Zones 4–9), heuchera (Heuchera spp. and cvs., Zones 3–8), hostas (Hosta spp. and cvs., Zones 3–8), and penstemons (Penstemon spp. and cvs., Zones 3–8). A quick tidy-up will refocus the viewer’s attention upon the plant’s other worthy attributes for the remainder of the growing season. Removing the spent flowers of rampant self-seeders like columbine (Aquilegia spp. and cvs., Zones 3–8) or Jerusalem sage (Phlomis tuberosa, Zones 6–9) will minimize unwanted seedings. With this group, only the flower stalks are removed.

Some plants, like peonies (Paeonia spp. and cvs., Zones 3–7), flower only once during the growing season and rely on robust root systems to increase their size and vigor. The removal of senescing blooms will minimize the energy that is directed toward seed production and divert that energy toward overall plant health, production of new foliage, and root formation. This in turn translates into more flowers for the next growing season. Other examples in this group include bearded irises (Iris germanica, Zones 4–9) and kniphofias (Kniphofia spp. and cvs., Zones 6–9).

If you appreciate the architectural and textural qualities of spent flowers and seed heads or the benefits of leaving seed heads in place as a food source for birds and other creatures, it is perfectly acceptable to forgo deadheading or cutbacks. But if your main goal is to keep a flowering perennial looking good longer, a little deadheading can go a long way.

 

—Adam Glas is a garden supervisor and rosarian at the Scott Arboretum of Swarthmore College in Swarthmore, Pennsylvania.

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