Why Do Coneflowers Flop Over?

Sun Conditions

• Coneflowers grow best in full sun, though they are often listed for partial shade or partial sun. The plants naturally seek the sun and send up long stems as a way of reaching through competing plants -- though none may exist. As they grow, they become spindly and unable to support the weight of any blooms or buds. Coneflowers should receive at least four hours of sun per day, preferable six, for sturdiest stem growth.

Water and Nutrients

• Coneflowers are U.S. natives, which in general are adapted to grow in poor soil with little water. In the garden, coneflowers may grow too quickly when they are in rich soil, are overly fertilized with nitrogen and get too much water. They prefer well-drained soil that is only moderately fertile, and that has a pH level between 6.0 and 8.0. Too much water, aside from fueling too-fast growth, can contribute to stem rot and to the plant dying off after a few years. If you choose to fertilize coneflowers at all, do so lightly and at the beginning of the season just as new growth appears. Clemson Cooperative Extension recommends a 12-6-6 nitrogen-phosphorus-potassium product at a rate of 1 pound per 100 square feet of planting area.

Cultivar

• Though a native plant, coneflower has been heavily hybridized, and you can find numerous named cultivars in an array of colors and sizes. Some, especially older hybrids, are more apt to flop than others that have been bred to be shorter or with sturdier stems. A 2009 study of 43 cultivars by the Mt. Cuba Center, a public garden and horticultural research facility in Delaware, found that several varieties, notably "Razzmatazz," "Pink Double Delight," "Hope," "Evan Saul," "Katie Saul" and "Matthew Saul," tended to flop more than others in the trial. "Pica Bella," "Elton Knight," "Fatal Attraction," "Fragrant Angel" and "Tiki Torch" were noted for their upright habits and sturdy stems.

Stop the Flop

• When moving or replacing your floppy coneflower is not an option, and holding back water and fertilizer doesn't help, you can control its tendency to flop with staking or pruning. Grow-through flower supports intended for peonies are helpful and unobtrusive if set in place early in the growing season. You can also prune your coneflower back by one-half in late spring to early summer, or whenever they are about 2 feet tall. This may delay flowering by two weeks.