To every perennial there is a season — often fleeting. Remember the peonies? Gone in one glorious week.
Yet some perennials have more staying power, especially with a little help. Conscientious deadheading often prolongs a plant's flowering. Cut some perennials back hard after their first flush of bloom, and they'll come back with a whole new burst of flowers later in the summer.
"Deadheading" is the practice of removing an individual flower that has started to turn brown or shrivel. The goal is to prevent the flower from turning into seeds. Once that plant has created seeds, it figures its reproductive job is done and it can stop flowering. If you remove the bloom, many plants will go back to work and try again to make a seed by creating more flowers.
Not all perennials will flower again after deadheading, but removing spent blossoms just looks tidier. "You need to deadhead," says Tim Pollak, outdoor floriculturist at the Garden. "Make it part of your weekly routine." It's neatest to remove not just the flower but its stem.
"Cutting back" refers to a more severe pruning. On some plants it means trimming individual stems back to where they branch. For other plants, it can mean cutting all stems back to a few inches, so they put out a whole new batch of stems, leaves, and flowers.
Tickseed (Coreopsis spp.), such as that in the Sensory Garden, is an example of a plant that responds well to deadheading, according to Pollak. "It has a long blooming season anyway," he says. If you continue to deadhead, "you'll get blooms long into the summer."
Catmint (Nepeta spp.) is an example of a perennial that can be trimmed back almost to the crown once its first bloom fades. "Cut it back hard and it will come back strong," Pollak says.
Bee balm or bergamot (Monarda), another member of the indomitable mint family, also responds to deadheading.
If you cut back perennial salvias such as 'May Night' (Salvia x sylvestris 'Mainacht') after their first May bloom, they will likely rebloom in July. Some years there is time for a second deadheading and a last hurrah of blooms before frost.
Bleeding heart (Dicentra spectabilis) is a quintessential late-spring flower. But it will rebloom sporadically well into summer, in all but the hottest weather, if you cut the stems of spent blooms back to the next branch. The tiny sprout of foliage in the crotch will grow into a new flower stalk.
You can prolong the flowering season on old varieties of roses, which bloom only once, by attentive deadheading. Trim the stem back to the next branchlet or bud. Many newer varieties of roses are bred to rebloom at least sporadically after their first June outburst, but you will get more flowers if you deadhead. Careful deadheading is what prolongs the season in the Rose Garden until frost.
Some plants, such as columbine (Aguilegia spp.), rebloom on their own initiative. "Usually you get a second bloom out of Aquilegia," Pollak says, "especially as you start to get some cooler nights toward the end of summer."
Other plants that can be cut back to encourage more bloom include balloon flower (Platycodon gradiflorus) and zinnia (Zinnia elegans). Also, deadhead some annuals such as yellow-flowered alyssum (Alyssum wulfenianum), trailing lobelia (Lobelia erinus), million bells (Calibrachoa), petunias, and impatiens.
Of course, when you cut any plant back severely, it will take a few weeks to rebound. In the meantime, distract attention with another blooming plant nearby. It's a handy trick to have a pot or two of annuals that can be moved where they are needed to provide an attention-grabbing spot of color.
Plants need nutrients, light, and water to power new growth, Pollak says. Make sure perennials have rich soil, slow-release fertilizer as needed, and keep the soil properly moist. Annuals usually need more fertilizing to keep up the show, since flowering is an energy-intensive process.
And once that second flush of bloom appears, keep deadheading to squeeze out all the flowers you can.