Growing Perennials OH 23
Leonard Perry, Extension Professor
Perennials are flowering or foliage plants with roots that live from year to
year and tops that may or may not die back
in the winter, depending on the particular plant. They include such popular flowers as delphinium, alyssum, columbine,
and primrose. Because many perennials prefer a cool climate, they are one group of plants that grow quite well in
Vermont and often better than in locations further south.
Perennials can be grown in a garden bed by themselves, in front of shrubs, under trees, or mixed with annuals.
(Annuals are those flowering and foliage plants that live and bloom for only one season, are killed by frost, and must
be replanted the following year.) Although perennials live from year to year, they are not really permanent because
they require replanting, dividing of old plants, and reworking of the soil. Perennials also are not really substitutes for
annuals. Most annuals bloom for much of the summer with often quite spectacular displays of color. Perennials, on the
other hand, often bloom only over a period of 2 to 4 weeks, with a much less striking display than annuals such as
petunias, impatiens or marigolds. Yet perennials offer something different, and the home gardener can have blooms all
summer by carefully choosing a combination of perennials.
Soil preparation: Because perennials are in one place for several years, proper preparation of the soil at the
beginning is important. The soil should have good drainage, but retain adequate moisture in the summer. Most
perennials do best in full sun, although many tolerate shade, and some even prefer it. (See OH 9, "Flowers for
Begin by spading the soil to a depth of 8 to 10 inches. Remove any rocks, roots, or large stones. If the soil is very
sandy or a heavy clay, add organic matter such as rotted manure. The heavier the clay soil, the more organic matter
you'll need to add.
Test the soil to determine if lime and nutrients are needed. (Soil test kits are available from your local Extension office
and many garden dealers.) If a soil test isn't done, add a complete fertilizer such as 5-10-5 at the rate of 1 1/2 pounds
(3 rounded cups) per 100 square feet. Add ground or dolomitic limestone at a rate of 5 pounds (7 rounded cups) per
100 square feet. It is better to mix the fertilizer with the soil and wait a week, or until it's rained, before adding lime.
The soil is ready for planting after you've mixed the ingredients with the soil thoroughly, and raked it smooth.
Planting: It is easier to start perennials from purchased plants, although some plants may also be started from seeds,
divisions, or cuttings. Perennials may be planted almost anytime during the growing season, but spring planting is
preferred. Plant after the last frost (usually mid-May in the warmer parts of Vermont, and mid-June in the colder
Remove the containers before setting plants in prepared planting holes. If plants are in peat pots, remove the top edge
of the peat pot to prevent it from acting as a wick, drying out the pot after planting and injuring the roots.
Give the plants space to grow over the next few years. This often is 1 to 3 feet apart, depending on the size of the
young plant. Perennials usually show up best when planted in clumps or groups of plants of the same variety. After
planting, be sure and water thoroughly--about 1/2 to a full gallon of water per plant and keep the perennials watered
during the summer. This is especially important for a few weeks after planting. (Although many survive dry spells, they
will grow better when kept well watered.) A light sprinkling of fertilizer around the plants 4 weeks after planting will aid
Mulching: Plants should be mulched after planting, in the fall, and each spring. In addition to adding organic matter to
the soil, mulch in the summer helps conserve moisture, moderate soil temperatures, prevent clay soils from baking and
cracking, and reduce weeds. During the winter a mulch helps to protect newly planted perennials and keep soil
temperatures warm, and to stimulate new growth which is easily killed by cold. Apply a fall mulch after several killing
frosts--usually October or November, depending on where in Vermont you live.
Staking: Many perennials grow tall or get top-heavy and require support; so gather in a supply of stakes, such as
wood dowels, bean poles, or bamboo. Stake tall plants, such a delphiniums, or top-heavy ones, such as peonies,
when they are set out. They will grow to cover the stakes and can be fastened to the stakes as they grow with plastic
tape or green twine.
Dividing: Never leave a perennial planted in the same place for more than 3 years. The center of the clump will grow
poorly and the flowers will be sparse. The clump will deplete the fertility of the soil in which it is grown and the plant
will crowd itself.
Divide mature clumps of perennials. Select only vigorous side shoots--the outer part of the clump--because this is the
part that will grow best; discard the center of the clump. Plants should be divided into clumps of 3 to 5 shoots each.
Be careful not to over-divide; too small a clump will not give much color the first year after replanting.
It is best to divide perennials in the spring so the new plants will have all season to grow. The exception is perennials
which bloom in spring or early summer such as peonies. Divide these in early fall.
Do not put all the divisions back into the same area that the original plant came out of because they'll be too crowded
and there will be poor air circulation around them. Discard extra plants, give them to friends, or plant them elsewhere
in your yard.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Lawrence Forcier, Director, UVM Extension System, Burlington, Vermont. University of Vermont Extension System and U.S. Department of Agriculture cooperating, offer education and employment to everyone, without regard to race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status.
Last reviewed 2003