If you haven't started working in your yard -- if it's been too wet or you went bicycling when it was sunny--it's not too late for the following list of things to do within the next two weeks:

1. Prepare your soil.

If your drainage is poor--you have puddles after a rain--take a deep breath and double-dig. Make a trench one foot wide, one foot deep. Put the soil you dig up at one end of the bed--you will use it to fill the next trench. Loosen the soil at the bottom of the trench to an additional depth of one foot. If the soil is compact, loosen it by sinking into it the tines of a spading fork. Dig a second trench the same way but throw the soil--mixed with peat moss or manure or some other loosening agent--into the first trench. Go on digging the rest of the yard in this manner. Comfort yourself with the thought that the strain on your back will pay off in more tomatoes, better eggplants.

When digging--whether double or single--make sure you break up all clods. Remove stones and weeds and debris. It's always a surprise how many rocks--including some big ones--find their way into your topsoil that you think is well tilled. What depth do they come from, one might ask--is the earth always in motion? I dig up my yard every year, and last year I hit upon an intriguing piece of rust-eaten machinery that my son Danny, 10, promptly identified as "an antique roller skate."

But just digging is not enough. Always mix in compost, leaf mold, wood ashes from your fireplace, well-rotted manure or fertilizers. Rake the soil smooth and level until it's a delight to the eye.

2. Now you are ready to plant any of the following early-spring vegetables: asparagus, beets, broccoli, brussels sprouts, cabbage (standard and Chinese), carrots, cauliflower, celery, chard, garlic, kale, kohlrabi, leeks, lettuce, onions, parsley, parsnips, radishes, rhubarb, shallots, spinach, turnips.

Peas are the only cool-weather vegetable that are too late to plant. And in view of the possibility of a hot May, it is a good idea to plant seedlings--rather than sow the seeds--of broccoli, brussels sprouts, cabbage, kale, kohlrabi, leeks, parsley and, most particularly, lettuce. Market packs are now available in nurseries.

3. Plant and transplant trees and bushes.

Consider establishing a berry patch. Perhaps the easiest to grow and the most rewarding in our area is the red raspberry.

Raspberries are grown in rows about two feet wide, or along a fence. They need supports: six-foot oak stakes, tripods or a system of posts and crosspieces with wires attached to the crosspieces.

Raspberries need full sun and thrive in clay as long as it is loosened with peat moss or manure.

For those who object to being pricked by thorns, U.S. Department of Agriculture geneticists have developed a new blackberry called Hull Thornless. Introduced in 1981, Hull Thornless is available to growers for the first time this spring.

"The thornless plants certainly make cultivation of blackberries more desirable," says Dr. Gene Galletta of USDA's Agricultural Research Service in Beltsville. Galletta calls the new blackberry highly productive and perfect for home gardeners and pick-your-own farms. It matches Black Satin in yield and fruit size, he says, and its fruit is "firmer, sweeter, tougher and keeps its color better than Black Satin does."

A smart idea: Plant the top--or the crown--of the horseradish root, which plays so prominent a role in the Passover dinner. Horseradish is not finicky about poor soil, and the odds are 4 to 1 that it will sprout quickly and that its taproot will thicken into a fat bulb. Caution: horseradish spreads, so plant it where it may be contained. The foliage is extravagant--the flowers are insignificant--but the best part is that next Passover you'll be able to use your own horseradish root and give away plenty more.

Correction: Bethesda master Gardener Henry E. Allen does not counsel against spring planting of parsnips, as I mistakenly wrote in this space last Sunday. What he says is that parsnips are not a spring crop but that parnsip seeds should be sown around April 1--and up to May 15--because they take 120 days to mature, and they taste best after the first frost. The variety he has been growing is called Harris Model, which he recommends highly. "Parsnips may be left in the ground during winter," he says, "and they can be dug in February or when needed."