Perennials are plants which live for two or more years. Some perennials in warm climates are grown as annuals in colder northern regions. Many other plants, including trees, are by definition perennials. Here we are referring only to ornamental plants with little or no woody stems.
These plants may be long lived or last only a few years. Most will bloom only one time in the growing season and will need pruning to keep attractive. Almost all will begin to decline if not thinned as the central root clump becomes too large.
Some perennial plants are grown for foliage, such as ferns and ornamental grasses. Other varieties are grown for blossoms, and may bloom either in spring or as late as fall. There are wide assortments of colors, blossom size and shapes. The advantages of perennials are that they are permanent—no need to replant yearly—and they are easily divided and moved to new beds.
Selecting: Consider the amount of sun and shade in your garden. Some perennials grow well in the shade and others must have full sun or at least full morning sun to perform optimally. Also try to determine what type of soil you have—sandy, high clay or good loam. A soil test will help. These facts are important because the site you choose for your perennial may be its home for several years.
Next, decide on the design; do you want foliage or blossoms? Decide on the color and height which fits best in your garden. Factor the blooming time into your overall plan. We are fortunate to have excellent garden centers with a wide assortment of plants to choose from, as well as those available online.
Planting: With perennials you have only one chance to prepare the bed properly. A soil test will serve as a guide as to what nutrients are needed and if any adjustment to the pH (acidity) is indicated. All soils, especially those high in clay or sand, will benefit from generous amounts of well composted organics tilled into the soil.
The method of planting is different from plant to plant. Some are planted as bulbs or other root structures and others are whole plants. A general rule is that spring blooming perennials should be planted in fall, fall bloomers planted in spring.
All plants should have proper spacing to accommodate their adult size. Sprouts and transplants should be planted in a generous sized hole at its original depth. Bulbs and rootlets all have different preferred planting depths and for some, such as peonies, this is very important for proper blooming. After planting water thoroughly and add a 1-2 inch layer of mulch.
Fertilization: Perennials may be fertilized with a slow release balanced fertilizer at the time of planting. Thereafter, they chiefly will need a source of nitrogen either as commercial fertilizer or an organic preparation. They may be fertilized in the fall after the first frost or in early spring. If they receive too much nitrogen, they, like most plants, will mainly grow leaves and stems, not blossoms.
Irrigation: Perennials will need at least 1 inch of water per week in order to perform best. Mulch will make a huge difference in water conservation for these and all plants, especially in the hot summer.
Fall and Winter Care: The tops of many perennials die in the fall. These may be cut off a few inches from the ground in the fall if you choose. Many people leave the tops until spring; some have attractive winter foliage, others have seeds for the birds. All of the tops will have some mulch-like effect, conserving water and moderating temperatures.