At this point, it's tough to say just what you should be doing in your garden this weekend. The weather's been so lousy that many gardeners aren't far enough along to tackle chores that normally are already done at this time of year. On the other hand, there are some gardeners who are now close to the proper timing for many crops because they did many spring chores last fall.

If you're still waiting to get into your garden or only now getting into it, there's a parcel of things to be done. Almost any vegetables or flowers can go in now. If you think you're not going to have time to do it all at once, here are some hints on priorites.

Plant trees, shrubs and perennials first. If put in much past the first of May, they get a little iffy. You want them to go in while pretty close to dormant. If you have several perennial plantings and can't do them all, you can get away with leaving your rose bushes out of the ground for another week, as long as you keep them in a cool, shaded place and make sure their roots are kept moist.

If you have a lot of trees to put in, and you only want to do a few this weekend, store the leftovers this way: Dig a trench a foot deep. Lay the roots in the trench so that the trees lie at an angle. Cover the roots with soil and lots of mulch. For mulch you can use anything organic -- newspaper, burlap, whatever. Water the works well and and leave them alone until next weekend when you get them into their permanent homes.

Apart from that, if you've bought a perennial and can't figure out where to put it -- something I've done often -- don't just let it wither and die. Punch drain holes in the bottom of a big box, bucket or any other container (a small trash can does well), fill it with good rich soil and give your perennial a healthy temporary home until you've gotten your act together.

As far as annual vegetables and flowers are concerned, if you're just beginning your garden, ignore tomatoes, peppers, eggplant, squash and beans for now. Concentrate on broccoli, cabbage, onions and potatoes. Those are the musts if you want to get anything out of them as a summer crop. Vegetables such as radishes, beets, lettuce and carrots can go in now and forever. I plant that group every few weeks throughout the season, so you can do them as you find the time and and make the space. Most annual flowers can still wait a week or two before going in, and I have planted many varieties after Memorial Day and still seen some handsome and profuse blooming.

For those determined gardeners who were able to get into their plots and plant early spring vegetables, this is the big weekend to begin thinning seedlings. It is the garden chore I dislike the most, largely because it seems so heartless. You have to choose, I've concluded. Either you thin and thereby achieve large beautiful heads of lettuce, round beets and fat carrots, or you spare the weaker seedlings and get a lot of small stuff. If you are into showing, thin now. If not, wait and pull your crowded beets and lettuce a few at a time as the season progresses and use them in salads and so on. By the time the last vegetables from a given sowing are harvested, they'll have the size and beauty you would have had in all of them had you thinned at the start.

Late last spring, I planted carrots thickly and never thinned them out. By the fall, I had a marvelous crop of enormous carrots, but I am quite sure that not all the seeds germinated, so I was saved by nature. That doesn't always happen, and you may wind up instead with small, misshapen carrots.

If you are a gardener of the diligent sort, and your brassicas are all in and doing well, you may want to add tomatoes, peppers and squashes to your plot. Just keep a few hotcaps handy. The official last frost date for this area is around May 10, depending on where you live, and with the weather we've had this spring, there's no telling what could happen. These tropical plants do not tolerate any kind of frost. TV GARDENING: A new show, "The Good Earth Garden," was launched a month ago on the Maryland Center for Public Broadcasting stations (Channels 22 and 67) at 2 p.m. on Sundays. Hosted by Tina James, the show is a leisurely half-hour in James' own garden near Baltimore. James gives viewers a knowledgeable look at some of the ins and outs of organic gardening, which she readily acknowledges is "an inexact science." She doesn't display the no-nonsense professionalism of Bob Thompson, who replaced the late James Crockett on PBS' "Victory Garden." But she offers ideas and a spontaneous approach to gardening that is likely to be endearing to the average gardener. DUMBARTON OAKS -- Season passes are $10 for individuals and $20 for families, providing unlimited visits to the Georgetown gardens through October. Admission is $1 to non-pass holders; children under 12, free. Call 342-3200, or buy them at Dumbarton Oaks museum shop at 1703 32nd Street NW, or write Garden Passes, Dumbarton Oaks, Washington D.C. 20007. For recorded information about flowers in bloom, call 338-8278; for tour information, call 342-3212..