Planting and Care

Perennials can be purchased in a number of ways. The most common way is plants in quart, one or two gallon containers. These plants are already growing and afford the gardener the flexibility to select and plant through the growing season. Another way is bare root or packaged plants. These are obtained through mail order or at garden centers and are sold as dormant material. These are available for spring planting only. If these materials are received at a time that they can not be planted immediately, keep the plants cool and keep the roots moist. They can be held for several weeks this way, thus assuring their survival prior to planting.

When to Plant

Most perennials are best planted in the spring. However, with the availability of material in containers, the planting season often extends well into the summer and early fall with autumn planting continuing until the first of October. The earlier perennials are planted the better the root system will be when the plant enters the winter. Late fall plantings can sometimes result in frost heaving and loss of perennials.

Planting Depth

Containerized perennials should be planted at the same depth they were grown in the container. Planting too high results in plants drying out and too low invites crown rots. Some perennials such as bleeding heart, iris and peony need shallow planting in order to flower properly. Containerized plants should be watered before planting and bare root perennials should be soaked in water for one hour prior to planting in order to rehydrate the plants.

Transplanting

Most perennials are transplanted in the spring as growth starts or in the late summer or early fall. It is usually best to wait until the plants have flowered and then cut back by half just prior to moving. If plants are moved out of season, they may need to be shaded for several days to allow them to recover.

After Planting Care

Mulching

Mulch provides a number of benefits. They help to make the garden appear neater, conserve soil moisture, retard weed growth and moderate soil temperatures. There are a variety of materials that can be used as mulch. Examples would be bark, dry grass clippings, and hulls of various sorts. Mulch should not be applied right up to the crown of the plant to avoid problems with crown rots. Leave some air space between the mulch and the crown.

New perennial beds are mulched right after planting with about 2 inches of mulch. Additional mulch is applied annually as needed so that the overall depth doesn’t exceed 2 inches. Apply additional mulch in the spring as soils start to warm. Most perennials will not need additional mulch in the winter if soils have been properly prepared and the drainage is good. The exception would be for perennials that have been transplanted or planted late in autumn. Here, a 3-4 inch layer of loose mulch like straw, or evergreen boughs applied after the soil is frozen, helps to avoid frost heaving.

Watering

Water is a vital part in getting newly planted perennial gardens established. Soak the plants initially after planting and then check regularly to prevent drying out. Mulching helps to cut down on watering frequency. The general rule of thumb of one inch of water per week for established plantings holds true. Less frequent but deep watering encourage perennials to root more deeply and thus become better able to handle drought conditions.

The most common and time efficient way to water perennial gardens is to use soaker hoses. Many perennial gardeners will snake a soaker hose through the garden and leave it there all summer. When water is needed they will connect it to a faucet and turn it on. To make the hose invisible, bury it just under the mulch.

Fertilization

Most perennials do not require large amounts of fertilizer if the soils have been prepared properly. Many overfertilized perennials will produce excessive, soft growth and produce very few flowers. Many times, perennials will tend to "lodge" or open up when overfertilized.

As a general rule, unless a soil test indicates otherwise, perennials can benefit from one pound of nitrogen per 1000 sq. ft. Granular fertilizers with a formulation of 12-12-12, 10-10-10, 5-10-5 or similar are sufficient.

Weed Control

Weeds that do appear in perennial gardens are often best controlled by shallow cultivation. If the weeds are perennial in nature, quick action is needed so that the infestation does not get out of hand. Cultivation again is the key, or you can make a very selective and directed application of glyophosphate to the weed. Mix the material as directed in a small container and use a foam paint brush to physically paint the weeds with the herbicide. This method prevents drift reducing damage to desirable perennials.

Fall and Winter Care

Many perennials are better left standing over the winter than cutting them down. There are several reasons for this. In addition to many of the perennials having attractive foliage and/or seed heads, they offer food resources for birds. Many birds find the seeds of perennials particularly tasty. The stems of perennials also offer a place for some birds to hide during the winter. With some marginally hardy perennials, leaving the stems up for the winter aids in overwintering. The foliage helps to insulate the crowns. Mums seem to benefit a great deal from this practice. Another reason to leave stems stand is that if the perennial is a late riser in the spring, the stems will help to mark the spot and prevent any accidental digging in the area that might harm the underground portions of the plant

Cutting back perennials in the fall may be something you would want to do especially if you were bothered by foliage diseases. Removing the old foliage would be a positive in this case as it helps to reduce the amount of innoculum present to re-infest next year’s foliage. Removing foliage can also be one of pure aesthetics. Some gardeners like to see standing perennials in the winter and others don’t. When perennials are cut down, do so after they have gone dormant. This is usually after the plants have experienced several hard frosts. Cut the plants down to within 2-3 inches of the crown. Cutting too close can result in winter injury on some perennials due to the fact that the buds for next year’s growth are right at the surface or higher and not below the soil line.