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How to Succeed with Perennials
Plant Selection
Select the right plant for the location to improve growth and reduce maintenance. Perennials for sun need at least six to eight hours of direct sunlight each day.
Soil Preparation
Preparing the soil properly before planting will reduce maintenance down the road. The planting bed should be weed free with all roots removed by hand or by spraying with a non-selective herbicide like Ortho’s Roundup. Organic mater like soil conditioner, finely ground bark or compost should be mixed into the soil to hold moisture and aerate the soil. Ideally, the bed should be prepared to a depth of 24 inches, allowing for maximum root development.
Prior to planting, fertilizer should be mixed into the soil, according to soil test results.
Planting Perennials
Container-grown perennials should be planted at the same level they are growing in the pot. Be sure to loosen up the root ball and tease the roots, so they’ll grow outward rather than the established circular pattern. Direct seeding of perennials into the soil is not generally advised, since it takes two or more years for perennials to bloom when grown from seed.
Water plants thoroughly. A deep soaking will help send roots downward to search for water. During the first year after planting, beds should be watered whenever dry to the touch about 1 to 1 ½ inches deep. In succeeding years, established perennials can be watered as needed, usually only during drought.
Mulch
After planting, apply a one to two inch layer of organic mulch like bark, cocoa hulls or cedar chips. Take care not to smother crowns or the shallow rhizomes of plants like iris. Mulch will help suppress weed growth, hold moisture and keep roots cool.
A little weeding may be necessary in perennial beds for the first few seasons. Weeds may be removed by hand or prevented with a pre-emergent herbicide like Preen. Some perennials, which multiply by reseeding may be inhibited if Preen is used. Hoeing or cultivating is not recommended, it stirs up weed seeds in the soil, encouraging weed growth and may damage shallow roots.
A winter mulch is recommended, especially for young plantings. Snow is the ideal winter mulch but is not reliable. A layer of light, fluffy, insulating material, such as straw or evergreen boughs, applied after the ground freezes, will prevent heaving. Apply in November or December and remove before growth starts in March or April.
Maintenance
During the growing season, remove spent flowers and developing seed pods, a process called deadheading. This will help prolong the bloom season of many plants. Seed pods may be hand picked or in some cases the whole plant may be sheared, (i.e. Campanula and Coreopsis.) Deadheading may also prolong the blooming period of heavily flowering plants like Gaillardia and Coreopsis grandiflora. Some seed pods are ornamental and may be left to persist over winter. Examples include; Siberian Iris, Rudbeckia, Sedum, and ornamental grasses.
Certain plants, like chrysanthemums, benefit from pinching during the growing season. The tips of the plant are removed, resulting in a bushier, shorter plant. Unpinched mums will get tall and leggy and will bear only a few flowers per stem. Pinch 2 to 3 times, starting when the plant has reached six to 12 inches, the last pinch should be no later than July 15, or flowering may be affected.
Winterizing & Dividing Perennials
Perennial beds can be cleaned in the fall or spring – the choice is yours. In the fall, clean up plants after frost kills the tops of perennial plants. Cut tops back to the soil line or leave a few inches above ground so plants can be identified in spring. The cleanup may be postponed until spring as the dead tops help to trap snow and leaves as mulch.
As the garden grows, plants expand and may begin to crowd one another. Dividing plants will help thin overcrowding, rejuvenate aged clumps and propagate choice varieties. This is best done in spring before growth is six inches or more, or in late August through mid October. Fall-divided plants will need their foliage cut back to four to six inches. Lift plants from the soil, shake or hose off excess soil and separate the crown with a knife, spade, axe or saw. Cut into sections with three to five eyes or buds for the best size blooming plants. Replant immediately and water well.
Dividing perennials is best performed in late afternoon or early evening out of direct sunlight. This will eliminate additional stress from the hot sun.
