For many, this weekend truly marks the start of the garden year. Freezing temperatures are gone, and the soil has warmed up considerabley in in the past three weeks, enough to motivate seedling plants to root and develop foliage. Starting now and continuing for the next three weeks, it's bedding-plant time in the Washington area.

Haste makes waste, as veteran flower growers privately admit after having spent untold sums of money on May bedding plants to lose them to decimating Washington summer temperatures and drought. Their experience suggests the plants are to blame, but such is not the case. The problem is the hurry to get the plants in the soil as soon as possible so the garden is planted and growing.

If past bedding gardens have not met your expectations for one reason or another, improve the soil before reaching for the trowel to bury your newly acquired annuals and perennials. Shop for your plants, by all means, and move them into the morning sun for momentary keeping, but critique your bedding garden before you shop.

Some obvious ground rules come to mind.

Know your garden, then choose plants accordingly. How much sun or partial shade do you have for planting? Impatiens are a wise choice for partial sun, but they perform even better in near-total shade. Try zinnias there, and they go into limbo. Coleus in total shade are a better performer than coleus in partial sun-shade. Marigolds are often destroyed by Japanese beetles, so planting them away from the rose garden could spare the blossoms for part of the summer.

Rely on your experience. Have you routinely watered well in past years, only to lose the plants for no seeming reason? Here, poor percolation of water into the soil could well have triggered the problem of root rot or dieback. Did you overfertilize and pay the price by growing plants without flowers? Did you neglect to mulch certain borders of the garden, only to lose the plants to wilt when you spent the weekend at the beach?

Begin with the soil. The foundation of your bedding garden has been in place for generations; what makes the difference between success and failure is how you improve the soil you have.

If your soil is sandy-loam and water drains like a sump pump, your problem is keeping nutrients in the soil, in which case you might drive toward the mountains and bag any leaves you find on the side of the country highways; spade all leaves and peat humus into the soil to retain water and provide decayed organic matter. Years of enriching sandy-loam soil this way will turn the tide.

Most gardens are not this blessed. Saddled with hardpan soil, gardeners have tried every available resource to improve their soil, but results have been deplorable.

Some gardens are worth saving because you cannot wait for better flowers next year. In this case, you might consider these options: Make repeat applications of gypsum soil conditioner to the flower bed, to the point that a fresh application would be made when the snow color of the last application starts fading in the soil. Assuming 10 to 15 treatments are made this year, the gypsum would start breaking down the hardpan by creating pockets subsequently filled with oxygen and calcium. The major constituents of clay soil (aluminum and iron) would then start dissipating, resulting in a gradual transition from hardpan to loamy soil. Atop the existing flower bed apply a thick layer of mixed sharp sand and peat humus, which then is spaded into the top inch of soil. Substitute products for the peat humus are composted leaves (leafmold) or Compro from the Blue Plains sewage treatment plant. Use equal amounts of sand and the other product in every case. Afterward, measure the flower bed to have an accurate estimate of the square footage, then take two soil samples at a depth of four inches and have the garden tested for pH. Let the manager calculate the required pounds of pulverized limestone for your garden. Repeat applications might be made to raise the pH to 6 to 6.5 or so. Many fertilizers lend themselves to flower beds, but best results are usually had with 5-10-5 or 10-10-10 inorganic products. For every 100 square feet, the rule is to work three pounds of either fertilizer into the top inch of soil before planting. An empty one-pound coffee can holds 2 1/2 pounds of fertilizer, so estimate accordingly.

This is also the time to use leftover wood ashes from the winter fireplace, as they are a good source of potassium. However, the best source is potassium sulfate (0-0-50) at the rate of one pound for every 500 square feet of bedding space; do not use potassium chloride 0-0-60 (also known as Muriate of Potash). Decayed leaves from the compost pile also should be worked into the soil. Don't till the garden! You can't improve the soil without working some materials into the garden, but do not till the soil with rototillers and the like. Tilling the soil precipitates soil erosion, so keep what you have and don't let it wash to your neighbor's garden.

Come October, I will have specifics on composting the bedding garden. Meanwhile, here are some specific ideas for what to plant where: Annuals for window boxes. Ageratum, alyssum, fibrous begonia, dwarf celosia, coleus, French marigold, nasturtium, dwarf petunia, phlox, verbena and dwarf zinnia. Annuals for foundations. Globe amaranth, sweetpea, California poppy, nasturtium and stock. Annuals for sandy and dry soils. Alyssum, cleome, gloriosa daisy, marigold, phlox, salvia, verbena and zinnia. Annuals for full sun. Ageratum, bells-of-Ireland, calendula, celosia, cleome, cosmos, dianthus, gaillardsia, larkspur, lobelia, marigold, morning glory, nasturtium, petunia, rudbeckia, salvia, scabiosa, snapdragon and zinnia. Annuals for partial shade. Amaranthus, alyssum, balsam, China aster, centurea, clarkia, cornflower, impatiens, nemesa, nicotiana, sweet alyssum, torenia and verbena. Annuals for fragrance. Alyssum, baby's breath, calliopsis, candytuft, cape marigold, bachelor's button, mignonette, nasturtium, nicotiana, pansy, annual poppies, sweet alyssum, snapdragon, sweetpea and thunbergia. Annuals for edging/borders. Ageratum, sweet alyssum, fibrous begonia, dwarf celosia, coleus, lobelia, dwarf petunia, nasturtium, phlox, verbena and dwarf zinnia. Annuals for backgrounds. Amaranthus, cosmos, larkspur, tall marigolds, tall snapdragon, tall zinnia, sunflowers, and tall celosia. Perennials for full sun. Achillia (yarrow), hollyhock, anthemis, arabis, English daisy, centurea, chrysanthemum, coreopsis, delphinium, globe thistle, geranium, daylily, hibiscus, red-hot-poker, lavender, liatris, lupine, pansy, evening primrose, rudbeckia, salvia and veronica. Perennials for partial shade. Aconitum, ajuga, astilbe, campanula, dictamus, foxglove, daylily, hosta, lobelia, lythrum, monardia, periwinkle and viola. Perennials for fragrance. Dianthus, iris, lily-of-the-valley and viola. Perennials for groundcovers. Creeping phlox, crownvetch, vinca minor, sedum, phlox, pachysandra and snow-on-the-mountain. Perennials for foundations. Chrysanthemum, iris and sweet William. Perennials for wet spots. Buttercup, bleeding heart, foxglove, Japanese iris, Siberian iris, and painted and Shasta daisy.

After planting, keep the bed watered every day for the first week to prevent roots drying out. Water in the early evening if possible. Mulch can be delayed until late May, so invest the dollars in plants.