Site Preparation: This is best done in the fall. First, have the soil tested and adjust the pH if needed. Check and adjust drainage. The next step is to dig the bed. Add 4 to 6 inches organic matter to heavy clay to improve soil texture. Dig to a depth of 12 or 18 inches and leave "rough" in fall or early spring. Finally, in spring, add fertilizer, spade again, and rake the surface smooth. 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.
Setting Out Transplants: By setting started plants in the garden you can have a display of flowers several weeks earlier than if you sow seeds of the plants. This is especially useful for annuals that germinate slowly or need several months to bloom. Buy only healthy plants, free of pests and diseases. Before setting out transplants, harden them off by exposing them to outside conditions during the day that will provide more light and cooler temperatures than they received inside. After the last frost date, annual plants may be set out. Dig a hole for each plant large enough to accept its root system comfortably. Lift out each plant from its flat with a block of soil surrounding its roots. Set the soil block in a planting hole and backfill it so the plant sets at the same level. Irrigate each hole with a starter solution of high phosphate fertilizer that is water-soluble. Follow package directions.
Watering: Do not rely on summer rainfall to keep flower beds watered. Plan to irrigate them from the beginning. When watering, moisten the entire bed thoroughly, but do not water so heavily that the soil becomes soggy. After watering, allow the soil to dry moderately before watering again. A soaker hose or drip tape is excellent for watering beds. Water from the soaker hose or drip tape seeps directly into the soil without waste and without splashing leaves and flowers. The slow-moving water does not disturb the soil or reduce its capacity to absorb water. Water wands are also good. Sprinklers are not as effective as soaker hoses. Water from sprinklers wets the flowers and foliage, making them susceptible to diseases. Structure of the soil may be destroyed by impact of water drops falling on its surface; the soil may puddle or crust, preventing free entry of water and air. The least effective method for watering is with a hand-held nozzle. Watering with a nozzle has all the objections of watering with a sprinkler. In addition, gardeners seldom are patient enough to do a thorough job of watering with a nozzle; not enough water is applied, and the water that is applied is usually poorly distributed over the bed. 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.
Mulching : Mulches help keep the soil surface from crusting and aid in preventing growth of weeds; organic mulches can add humus to the soil. Grass clippings make a good mulch for annuals, if they do not mat. Sheet plastics also may be spread over the soil surface to retard evaporation of water and to prevent growth of weeds. However, these materials are unsightly for use in the flower garden. 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 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: After plants are set out or thinned, cultivate only to break crusts on the surface of the soil. When the plants begin to grow, stop cultivating and pull weeds by hand. As annual plants grow, feeder roots spread between the plants; cultivation is likely to injure these roots. In addition, cultivation stirs the soil and uncovers weed seeds that then germinate.
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. Tall-growing annuals like larkspur, or tall varieties of marigold or cosmos, need support to protect them from strong winds and rain. Tall plants are supported by stakes of wood, bamboo, or reed large enough to hold the plants upright but not large enough to be conspicuous. Stakes should be about 6 inches shorter than the mature plant so their presence will not interfere with the beauty of the bloom. Begin staking when plants are about 1/3 their mature size. Place stakes close to the plant, but take care not to damage the root system. Secure the stems of the plants to stakes in several places with paper-covered wire or other materials that will not cut into the stem. Plants with delicate stems (like cosmos) can be supported by a framework of stakes and strings in crisscrossing patterns. 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.