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HERBACEOUS ORNAMENTALS -PERENNIALS, ANNUALS AND BULBS |
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KEY CONCEPTS
I. General Discussion of Perennials, Annuals and Bulbs
II. General Cultural Requirements of Perennials, Annuals and Bulbs
III. Perennials
IV. Annuals
V. Bulbs
Return to Introduction
PERENNIALS
There are many reasons gardeners choose to grow perennials. Perennials do not need to be planted each year. An all-perennial garden changes throughout the season. Perennials are easy to divide and share with other enthusiasts.
SPECIAL REQUIREMENTS OF PERENNIALS
Successful color combinations and continual color throughout the season are challenges facing gardeners who choose to grow perennials. Plot the blooming periods of the plants you choose on a linear calendar. This aides in developing continuous bloom and combining color combinations successfully.
Large plants may be planted singly. Plant smaller plants in clumps or "drifts" of 3, 5 or 7. Avoid planting in precise rows. Informal shapes are easier to maintain than formal groupings. Curved lines, varied plant heights, masses and textures result in a more natural appearance.
Careful attention to foliage is important with perennials because few perennials bloom for more than a few weeks. Texture, form, height and color should be combined carefully. In addition to a linear calendar, plotting the garden to scale will ensure that these factors will be combined successfully.
The bed in the following illustration was designed to provide continuous bloom from April to October.
Many perennials grown from seed take one or two years before they flower. If you have the patience, equipment and the space, grow perennials from seed; it is substantially less expensive. Many perennials may be seeded in June, then transplanted in early autumn.
When purchasing potted perennials at a nursery, avoid selecting plants in bloom unless you must be assured of a specific color. Remove any flowers at planting time to promote root establishment. The price of plants relates to the size and age of the plants. Newer cultivars are more expensive than cultivars that have been marketed for several years. Spacing of perennials is given in Fact Sheet 1236, Reference Herbac.4.
Gardeners, who enjoy collecting perennials, find that as plants mature they may wish to relocate some of them. Transplant perennials in early spring just after growth starts or in early September. To relocate perennials during the main growing season, remove all flowers and cut back foliage. Trimming of flowers and leaves reduces transplant shock. Water as needed for good establishment.
Perennials often stay in the same location for years. This means that selection and preparation of site for new plantings are vitally important. Organic matter worked into the soil at planting time can provide nutrients and improve aeration and drainage.
For perennials that require annual fertilization, apply in spring as new growth begins. Broadcast 1 pound of 5-10-5 or 6-12-6 over 100 square feet of area. Make another 1-pound application 8 weeks later. Wash off any fertilizer that remains on foliage. Astilbe, chrysanthemum, delphinium, lupines and summer phlox are perennials that should be fertilized annually. It is always best to follow recommendations of a soil test. Test soil every 3 years.
Winter mulching helps to prevent winter injury from HEAVING. After soil has frozen, apply a layer of coarse mulch. Four inches of pine boughs, pine needles or straw are suitable. Pull back mulch from plant crown as soon as new growth begins in spring. Winter mulching of perennials is especially important in the following situations:
- when marginally hardy perennials are grown;
- for newly transplanted or divided perennials moved in fall.
Perennials with heavy flower heads or long thin stems may require staking. The weight of water or wind can easily damage flowers and stems. Examples of perennials that usually need stakes or supports include delphinium, foxglove, Achillea 'Gold Plate,' selected asters and mums. Stake when plants are about 6 inches tall so supports are hidden by foliage later in the growing season.
DEADHEADING TO PROMOTE REBLOOM
The removal of spent blossoms is called "deadheading." Many perennials will continue to bloom if faded flower heads are removed. This is especially true of dianthus, coreopsis and shasta daisy. Some perennials will bloom again later in the season. Examples of perennials that will produce a second flush of blooms if flower stalks are cut back to the ground include delphinium and false indigo.
There are different methods of deadheading. Some plants will rebloom on the same flower stalk. In this case, it is necessary to remove only the dead blossom. Campanulas and balloon flowers will rebloom if faded blossoms are removed. Other perennials are deadheaded by cutting off old flower stalks down to where the new bud shoots appear. Obedient plant should be deadheaded in this manner. When deadheading, look for the location of the second bud or set of buds.
Although faded flower heads should be removed on all plants, only some will produce new blooms. Others will not rebloom. Removing spent blooms diverts energy that would otherwise go into seed production.
Garden markers and record keeping are very helpful with certain perennials. It is easy to forget about perennials that appear late in spring or die back before the rest of the garden. They are often "rediscovered" by accidentally digging into them. Good candidates for markers are butterfly flowers, Oriental poppies and balloon flowers.
Most perennials decline with age and should be divided every 3 or 4 years. New growth can be noticed on the outer edges of clumps. Divide perennials when you notice the following:
- a dead center formed in the crown area with a ring of growth around it;
- blooms becoming sparse and smaller;
- plants looking obviously crowded.
Do not divide perennials when they are in bloom. Divide midsummer and late-summer bloomers in spring (April or early May) when growth is 2 to 3 inches high. Divide spring-blooming perennials in late August or September.
To divide perennials, dig the entire plant and separate it into sections, or take divisions from the edge of the clump while it is still in the ground. Ornamental grasses have tightly tangled, tough root systems that are difficult to divide. Do not hesitate to cut through a large clump of roots with a sharp ax.
Some perennials are rarely divided or moved unless absolutely necessary. These include gas plants, peonies, tree peonies, foxtail lilies, goatsbeards, butterfly weeds and bleeding hearts.
After a killing frost, remove dead stems and foliage. Leave a piece of stem a few inches long to assist you in locating plants the following spring.
Powdery mildew is probably the most troublesome disease of perennials. It looks like the plant is covered with a dusting of white or gray. It is very unsightly, even though plants are generally not killed by the infection. Powdery mildew usually appears in summer when fungal growth is promoted by high humidity.
To discourage powdery mildew, choose sites that are sunny and have good air circulation. Maintain good air circulation by thinning clumps and providing room for plants to grow. Water early in the day and remove and destroy any infected foliage. Powdery mildew can overwinter on infected foliage and spread to new foliage the following year.
Insects that can attack perennials include aphids, plant bugs, leafhoppers, mealybugs, scales, thrips and whiteflies, red spiders and other mites, caterpillars, grasshoppers, beetles, and leafminers. Slugs are often a problem, especially in shaded gardens where mulch is routinely applied.
These are the primary problems that may arise with perennials. For assistance in identification and treatment of specific disease and insect pests of perennials see Extension Bulletins and Fact Sheets.
FACT SHEETS ON PERENNIALS
Iris 2038, 1240
Delphinium 1207
Hostas 1239
Peonies 1241
Chrysanthemum 1219
Best Flowers 1209
Shade plants 1243
Foliage Plants for Summer Landscape 1095
Ornamental grasses 1093, 1238 and
Bulletin 461
Flower Garden Weeds 1107
Plants for Screens 1064
Low-maintenance Perennials 1056
Plants for Wet Areas 1054
Perennials for Specific Sites and Uses 1242
Foliage Plants for Summer Landscape 1095
Crown Rot of Ajuga 3057
Ferns 1214, 1098
Ground Covers 3057, 1005, 1126
General Maintenance of Herbaceous Ornamentals 1236
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