Peonies, irises, daisies, coneflowers, salvias and other popular perennial flowers are gardening favorites because they are such low maintenance plants. Even the least-demanding flowers need a little attention occasionally, though, and some flowers simply perform better with periodic pinching, deadheading, watering, fertilizing and/or dividing.
Pinching is the practice of removing the tip of a shoot/stem on a plant. Removing the tip removes a bud, so instead of the shoot continuing to grow taller, it sends out branches along the sides of the shoot. Pinching creates shorter, stockier plants and delays flowering to a more desirable time in some cases.
Mums that are pinched two to three times over the course of spring and early summer are shorter, sturdier and more uniform plants. They will also hold off from blooming until September and October rather than producing a few sparse blooms in July and August.
Asters benefit from pinching in similar fashion to mums. Other choices are more subjective to the gardener and the growing location. For example, salvia, monarda, veronica, tall sedum, and other plants get leggy or floppy in some sites. Pinching them once in May makes them shorter and sturdier for the summer. In some cases, however, pinching may be unnecessary.
Deadheading is the practice of removing spent flower heads. This is also subjective. In some cases, such as some species of salvia, deadheading encourages a second flush of growth. With single-blooming daylilies and hostas, deadheading does little for the health of the plant but makes a big difference in appearance.
In general, if a perennial flower plant blooms all season like purple coneflower, leave the stems. If the stems are attractive after the bloom such as with astilbe, leave the stems. If the spent flowers are ugly or leave unattractive bare stems, cut them back.
Established perennials are deeper-rooted than annuals, so they require less frequent watering. Always water deeply and infrequently, and only water over extended dry periods. Frequent irrigation encourages undesirable shallow root growth and leggy/floppy plants. Many species will survive and still be healthy in most cases without any supplemental watering (even through the hot, dry months of Kansas summers).
Some perennials benefit from annual supplemental nutrition in spring. The major exception is for plant species that prefer poor infertile soil, such as butterfly milkweed (asclepias), blue false indigo, coreopsis, purple coneflower, hellebore, lavender, catmint, sedum, most groundcovers, and others. With too much fertilizer/nutrition, these plants get floppy and put more energy into foliage than blooms.
Another exception to fertilizing is for plants already growing in extremely fertile, well-drained soil with high organic matter content (a gardener’s dream). Gardeners who are diligent about adding compost to their flowerbeds may find themselves in this category.
Peonies, mums, daylilies, true lilies, tall garden phlox, and others like more nutrition. They are more robust and produce more flowers when fertilized properly. Fertilize in spring when new growth appears. A soil test is the best way to know what to apply.
Apply granular fertilizer alongside the base of the plant (sidedressing) or use a water soluble fertilizer in a watering can or through a hose-end sprayer. Organic or conventional fertilizer is the choice of the gardener, as well as deciding whether to use quick-release or slow-release fertilizer. Avoid fertilizing in summer or fall as plants may be burned or may put on lush growth just before freezing temperatures arrive.
Some perennial species, like yarrow, benefit from being divided periodically. Dividing basically means digging up the plant and cutting it in half or smaller pieces. Although the main reason to divide plants is to rejuvenate them, dividing is also an easy way to get more plants if they are needed or desired. In the case of yarrow, the center of the plant may die out over time, and dividing plants allows for the dead portion of the crown to be removed.
Divide fall-blooming perennials in the spring and most spring- and summer-blooming perennials in the fall. Avoid dividing perennials in hot, dry weather. Daylilies are the exception to most rules and can be divided in summer after they finish blooming.
— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation. She is the host of “The Garden Show.”