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FLOWER BED: PERENNIALS
  MG Manual Reference
Ch. 14, pp. 14 - 20

[ Perennials: culture and maintenance | controlling insects and diseases | asexual propagation ]


Perennials are plants that live year after year. Trees and shrubs are perennial. Most garden flowers are herbaceous perennials. This means the tops of the plants -- the leaves, stems, and flowers die back to the ground each fall with the first frost or freeze. The roots persist through the winter and every spring, new plant tops arise. Any plant that lives through the winter is said to be hardy.
There are advantages to perennials, the most obvious being that they do not have to be set out, like annuals, every year. Some perennials, such as delphiniums, have to be replaced every few years. Another advantage is that with careful planning, a perennial flower bed will change colors, as one type of plant finishes and another variety begins to bloom. Also, since perennials have a limited blooming period of about 2 to 3 weeks, deadheading, or removal of old blooms, is not as frequently necessary to keep them blooming. However, they do require pruning and maintenance to keep them attractive. Their relatively short bloom period is a disadvantage, but by combining them with annuals, a continuous colorful show can be provided. Most require transplanting every 3 years.
Culture and maintenance of perennials Top

Site Location. You need to consider many of the same aspects of site selection for perennials as you do for annuals; sunlight (full sun to heavy shade), slope of the site (affects temperature and drainage), soil type, and the role the plants selected will play in the garden. This is especially important with perennials, as they usually are left in the site for several years. In general, it is best to plant clumps of perennials rather than one plant. Large plantings may be made if space allows. An ideal location would provide a background such as a wall or hedge against which perennials will stand out while in bloom. In island beds, perennials can provide their own background if tall ones are planted in the center and low ones toward the edges.
Soil Preparation. Preparing the soil is extremely important to perennials. Many annuals can grow and flower in poorly prepared soil, but few perennials survive more than one year if the soil is not properly prepared.
For new beds, begin preparing soil in the fall before planting time. Have the soil tested first. Results will indicate how much fertilizer needs to be added during preparation and how much fertilizer needs to be added in the spring. Before preparing new beds, check the soil to see that it is well-drained, yet has some water-holding capacity. Test for drainage as described in the section on annuals. If drainage is inadequate, dig furrows along the sides of the bed and add soil from the furrows to the bed. This raises the level of the bed above the general level of the soil. Excess water can then seep from the bed into the furrows. Raised beds may wash during heavy rains. This can be prevented by surrounding the beds with wooden or masonry walls. Since raised beds dry out more quickly than flat beds (little moisture moves up into the bed from the soil below), water beds frequently during the summer. After forming the beds, spade the soil to a depth of 8 or 10 inches. Turn soil over completely, incorporating 2 to 4 inches of organic material. Remove debris and leave rough during the winter.
In the spring, just before planting, spade again. At this spading, add recommended levels of fertilizers. Be sure to work any phosphorous deeply into the soil, where plant roots can get it. Rake the soil surface smooth. After raking, the soil is ready for seeding or planting.
Selecting Plants. It is best to select plants with a purpose in mind, such as edging plants, accents for evergreens, masses of color, rock garden specimens, etc. With specific purposes in mind, you can choose perennials by considering their characteristics and deciding which plants best meet your requirements.
For a good display from a limited number of plants in a limited space, select named varieties. Observe the flowering times of perennials in your neighborhood. That way you will be able to choose plants that will flower together and plants that will be showy when little else is in bloom. The flowering time may vary as much as 6 weeks from year to year, but plants of the same kind and their cultivars usually flower at the same time. To obtain details on particular plants or groups of plants, consult plant societies, specialty books, nurseries which specialize in herbaceous perennials, and local botanical gardens.
Plants of many perennials can be bought a local nursery. These plants usually are in bloom when they are offered for sale, which allows you to select the colors you want. Buy perennial plants that are compact and dark green. Plants held in warm shopping areas are seldom vigorous and generally have thin, pale, yellow stems and leaves. Avoid buying these plants. Buy named varieties of plants for known characteristics of disease resistance, heat and cold resistance, growth habits and colors.
Many perennials do not grow true to type if grown from seed saved from old plants. If you plant seed you have saved, many off-types of color, flower form, and plant habit are produced. Purchased seed, whether hybrid or strains, usually give uniform results. You can sow perennial seeds directly in the beds where the plants are to bloom, or you can start early plants indoors or in a cold frame and set them out in beds after the weather warms.
Planting Times. Generally, late-summer or fall-flowering perennials are planted in the spring, while spring-flowering perennials are planted in late summer or early fall. However, it is wise to check exact planting dates for specific perennials. Regardless of the time of planting, perennials should be allowed sufficient time to establish themselves before blooming or the onset of cold weather.
Planting Seed Outdoors. Perennials seeded in the garden frequently fail to germinate properly because the surface of the soil cakes and prevents entry of water. To avoid this, sow the seed in vermiculite-filled furrows. For planting directions, see the previous section on annuals.
Setting Out Plants. Whether you buy plants from a nursery, mail-order source, or start your own indoors, set them out the same way. When the time comes to set plants out in the garden, remove them from flats by slicing downward in the soil between the plants. Lift out each plant with a block of soil surrounding its roots and set the soil block in a planting hole. If the plants are in fiber pots, remove the fiber from the outside of the root mass and set the plant in a prepared planting hole. When setting out plants in peat pots, remove the top edge of the pot to prevent it from drying out and limiting the root development of the plant. Thoroughly moisten the pot and its contents to help the roots develop properly. Drench the soil around the planting hole with a liquid fertilizer (16-12-10 or 20-20-20 mixed 1 tablespoon per gallon of water) to stimulate root growth. Set the moistened pot in the planting hole and press the soil up around the plant. Allow plenty of space between plants, because perennials need room to develop. Perennials usually show up best when planted in clumps or groups of plants of the same variety.
Watering. Since herbaceous perennials grow back from the roots every year, it is important to encourage healthy, deep roots. Proper watering promotes good root development. Make sure when watering that all the roots are reached. Follow directions on watering in the section on annuals.
Mulching. Mulch gives an orderly look to the garden and cuts down on weeding. Mulches are very useful for maintaining uniform moisture conditions in the garden. Soil temperatures are modified by mulches to various degrees. Organic mulches may add some nutrients and humus to the soil, improving its tilth and moisture-holding capacity. Most organic mulches should be applied after plants are well-established and when there is reasonably good soil moisture. Inorganic mulches, such as plastic films and paper, are applied prior to planting. Black plastic, landscape fabric and similar materials should be spread on land that has been completely prepared for planting and has a high moisture level. Bark, pine needles, and shredded leaves are common organic mulches used in perennial beds. Gravel and black plastic are inorganic materials to use. All mulches require care to keep them attractive; litter is very noticeable.
Perennials should be mulched during the winter months to protect them from the heaving that results from repeated freezing and thawing of the soil. However, you must be careful with winter mulching, as it can do more harm than good. Be careful not to pile mulch heavily over the crowns, as this would encourage rotting. Boughs of evergreens give ample protection but allow air circulation. Apply mulch around the plants only after the soil temperature has decreased after several killing frosts. If winter mulch is applied too early, the warmth from the protected soil will cause new growth to start. Severe damage to the plant can result from new growth being frozen back. Remove winter mulch as soon as growth starts in the spring. If you don't, new growth will develop abnormally with long, gangly stems and insufficient chlorophyll.
Weeding. Follow weeding directions in the section on annuals. A few preemergent herbicides are now registered for use in perennial flowers.
Fertilizing. Regular fertilization is necessary. Perennial plantings can rob the soil of its natural fertility. However, do not fertilize perennials heavily. A light fertilization program gives a continuous supply of nutrients to produce healthy plants. Use 5-10-5 fertilizer. Place fertilizer in small rings around each plant in March. Repeat twice at 6 week intervals. This should be enough to carry plants through the summer. Apply another treatment of fertilizer to late-blooming plants in late summer. Always water the bed after applying fertilizer. This will wash the fertilizer off the foliage and prevent burn. It will also make fertilizer available to the plants immediately.
Deadheading. After perennials have bloomed, spent flowers should be removed. Cut flower stems down to a healthy leaf or to the ground, if there are no more buds. This will keep the beds looking neat and will prevent plants from wasting energy setting seed. Delphiniums can be forced to reblossom if cut back severely after the first bloom.
Disbudding. To gain large blooms from perennials, as opposed to more numerous but smaller blooms, disbud them. In disbudding, small side buds are removed, which allows the plant to concentrate its energy to produce one or a few large blooms. Peonies and chrysanthemums are examples of plants which are often disbudded.
Staking. Most erect perennials are top-heavy and all of the taller ones need staking. If plants fall over, the stem will function poorly where it has been bent. If the stem is cracked, disease organisms can penetrate the break. Stake plants when you set them out so they will grow to cover the stakes. Once staked, tall perennials can better withstand hard, driving rain and wind.

Tied too tight
Use stakes made of any material. Select stakes that will be 6 to 12 inches shorter than the height of the grown plant. Place stakes behind the plants and sink them into the ground far enough to be firm. Loosely tie plants to the stakes, using paper covered wire, plastic, or other soft material. Tie the plant by making a double loop of the wire with one loop around the plant and the other around the stake. Never loop the tie around both stake and plant. The plant will hang to one side and the wire may girdle the stem. Add ties as the stem lengthens.

Tied loosely
The plants in the illustrations to the left have been tied too tightly. It is better to tie the principal branches loosely as shown in the illustrations below.
Fall Care. In the fall, after the foliage of perennials has died down, remove dead leaves, stems, and spent flowers. These materials often harbor insects and disease-causing organisms. Apply winter mulch after the soil temperature has dropped.

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