If you planted a flock of shrubs and trees this spring, you may not want to read further. By stopping here, you may not lose out on a glorious Memorial Day holiday weekend. So much for the good news.

Now for the bad news. If you didn't dig deep and wide holes, or if you merely dug a hole and planted the shrub or tree, then the plant is well on its way to the horticultural graveyard; it could be a fatality before the year is over or, worse, a slow but certain death over the next few years.

However, if you don't want dead plants and wasted dollars, then you'll probably want to postpone a few things today while you make tracks for the garden shop and your garden in an effort to save those plants.

The problem isn't the plants, but how you set them in the soil. In a way of speaking, you have a sump hole out there that collects water and kills the plant at the same time. However, if you rectify the mistake now while the plant has ample time to grow a network of horizontal feeding roots, then you will have saved the plant. Time is critical.

Actually, there are two landscape environments in the Washington area. First, there is the traditional hardpan soil that holds water in the fashion of a sponge; in clay soils of this order, there is no room for compromise. The hole must be perfect.

In sandy soils east and south of Washington, the challenge is not to provide perfect drainage, but to retain food in the soil long enough to be absorbed by the feeding roots of plants; digging copious amounts of leafmold, undecomposed leaves and other organic matter into the soil is the only solution. In new plantings, it would be advisable to create a subsoil barrier of clay to slow down the loss of nutrients, backfilling over the clay with a mix of sand and peat humus (or Michigan peat or leafmold).

Assuming your soil is hardpan, here is a scenario for saving the shrubs and trees planted earlier this spring:

As for supplies, you will need several (if not more) large bags of sharp sand from the hardware store; this is the sand used for making concrete. From the garden shop you'll need many bags of peat humus (or Michigan peat). A bag of ground limestone will help adjust the soil pH as needed.

Using a pointed steel shovel, dig balled-and-burlapped plants from the garden by loosening soil on all sides before attempting the final excavation. Move plants quickly to a shaded spot, hosing down the ball lightly to prevent wilting of foliage.

Return to the hole and excavate, discarding the soil taken up. Minimum width of the hole should be twice the width of the balled plant. Mimimum depth should be 1 1/2 times the height of the ball, but twice the height would be a superior hole. For balled plants less than 12 inches wide and less than l0 inches high, a hole of 2 feet wide by 14 inches to 16 inches deep is strongly urged.

At the base of the hole, apply 4 or 5 inches of sharp sand, which solves the drainage problem. Above this, apply a mix of equal amounts of sharp sand and peat humus or Michigan peat or composted leaves; make sure this is thoroughly mixed before strewing in the hole. Sprinkle water over the soil at this point.

Positioning the balled shrub or tree in the hole is critical because the top of the ball must be level with the soil surrounding the hole. Place the balled plant in the hole and check the position. Add or subtract soil as needed, then fill in around the balled plant with your sand-humus mix. When the hole is filled, add more water to settle the soil, then top with more soil as needed.

Finally, mulch with hardwood chips or chunks; do not use peat moss for reasons we'll explain in a column two weeks' hence. Orchestrate the mulch in the form of a wave some four inches' thick at the crest (refer to the sketch). Extend the mulch about 12 inches beyond the hole on all sides so as to ensure cool soil temperatures all summer long; cool soil temperatures assure continued growth of the horizontal feeding roots following the transplant up to late fall.

Since you have discarded the soil previously holding food for the plant, fertilize promptly for quick recovery of the plant. If you're in the dark as to what to use, ask the garden shop manager for advice when you buy your peat humus, lime and such.

Incidentally, this weekend is pretty much on spring deadline for buying and planting new shrubs and trees. Aside from the bargain prices and excellent selection, the plants have received regular care all this while, so there's little question about plant performance if you plant now and give it your best tender loving care.

Some weekend landscaping tips:

Move your indoor plants outdoors this weekend to benefit from the luxurious humidity from now on. Here is a partial list:The weeping fig (ficus benjamina) should be moved to the shade under the canopy of taller shade trees, if possible; top-heavy weeping figs will certainly topple over unless you shore up around the container. The tree will take direct sun if there is no choice, but this is hardly the way to treat the plant. Fruiting fig trees (ficus carica) merit full, unobstructed sun; continue fertilizing every week or 10 days with 15-30-15 up to Labor Day. Lantana needs full sun, as do all citrus plants and poinsettia. Remove your Easter lily from its pot and set it in the soil in a full-sun garden; water frequently the next two weeks to help the roots along. Amaryllis is moved outdoors in fairly dense shade (sun at sunrise is fine, but not later than mid-morning). Dig a hole 2 inches deeper than the plastic pot, discarding all soil taken from the hole. Put down 2 inches of gravel or stones at the base, then plant the pot. Cover the rim with wood chips to keep the pot cool. Stake the stalks so as not to lose the foliage, which is storing up sugar for the winter flowers. Fertilize with Peters' 20-20-20 every week for the next five weeks, halting plant food around July 4-6. African violets can be moved to a northern window and will flower steadily. If moved to an enclosed porch, expect even better results. Feed every other week with Peters' 12-35-14. Fertilize hydrangeas once more. PeeGee hydrangea (always white flowers) gets 15-30-15, MiracleGro or RapidGro; apply 2 gallons per plant. French hydrangea blossom color dictates the fertilizer. If flowers were blue last year, apply l tablespoon of Urea (such as Urea Ice & Snow Melter) in 2 gallons of water per plant. If flowers were pink, use any of the products suggested for the PeeGee hydrangea. Flowers should be along in five weeks.