Okay, now you can plant your tomatoes.

It's with a good deal of relief that I make that statement. The late arrival of spring, combined with the relatively warm weather we've had since then, made it very tempting to put in warm- weather plants. It seemed so natural to just slip those little guys right in between the cabbage and the peas. But it was wise to hold off and not risk losing them.

The most competitive tomato-growers put them in early and top them with hotcaps or cut-off milk jugs on nights with a threat of frost. That gives them a jump of maybe a week on other tomato- growers at harvest time. But you can make the same harvest deadline simply by planting patio varieties (bearing either full-size or cherry-type fruit) that come in very early because they spend less time developing foliage. Of course, they do provide a smaller yield than normal-size tomato plants.

Planting tomatoes isn't tricky, but taking a few basic precautions now will ensure strong plants with maximum harvests. I've been lucky never to have experienced the decimating effects of the cutworm, a caterpillar with the cute habit of chomping your favorite vegetable off an inch or so above the ground -- at night, no less. I'm told by less-fortunate gardeners that whole rows of seedlings can be wiped out in one night.

But cutworms are easy to control: Just wrap a piece of newspaper around the entire length of the seedling stem. For some reason, cutworms don't seem able to chew through newsprint. Don't use color sections: Color inks contain lead that will wind up in the soil and then in the plant and the vegetables you harvest.

Preparing the ground for tomatoes is pretty much the same as for other vegetables. I've read and heard people say that if the soil is too rich in nitrogen, you're likely to get much lush growth in the plant but few tomatoes. That may be true if you use chemical fertilizers, but if you use compost or manure, you can't overdo. Any good garden soil enriched with organic materials is perfect for growing tomatoes.

It's also good to throw a couple of handfuls of limestone into the ground around the plant. Hot, dry weather later in the season can bring on blossom-end rot. The lime provides calcium and thereby helps prevent blossom-end rot, which scientists believe is caused by lack of water and calcium at the crucial ripening stage.

Planting tomatoes is pretty straightforward. If the seedling is fairly large, lay it down horizontally in the ground, gently bending the leafy top upward out of the ground. Cover the entire length of the plant with soil, leaving only the top leaves and the top two inches or so of your newspaper collar exposed. If the seedling is small, just dig a hole deep enough to accommodate the entire stalk vertically in the ground. As the newspaper deteriorates -- which will happen fairly rapidly -- the stalk sends out additional roots that slurp up more nutrients and water, making a hardy, healthy plant.

You can go along, during the summer, heaping various organic mulches about the base of the plant as it grows, providing additional nutrients and retarding water evaporation.

Planting tomatoes in cages helps in a number of ways. First, it eliminates the need to stake the plants. I've grown tomatoes without staking or caging and I can tell you that it's a huge pain, not only because they spread all over the place and take up ridiculous amounts of space, but also because most of the fruit ends up right on the ground, where it develops rotted spots before fully ripe, or gets eaten by slugs, mice, turtles and anything else that happens along. Second, when grown in cages, the plants develop full foliage that helps prevent sunspot, soft and discolored areas on unripened tomatoes exposed to too much sun.

You can buy ready-made tomato cages at plant and hardware stores, but I've found the best ones are made at home with concrete reinforcement wire. The stuff is as sturdy as a gate post and lasts forever, it seems, despite the rust it will show after the first year. You can find it at most lumber yards, but call first to make sure they have it. Have them cut the wire into six-foot lengths, and, if they're really nice, ask them to remove the horizontal length at one end, which will give you little "feet" you can jam into the soil to hold the cage in place. Having the lumber yard cut the wire is important because it's very heavy and requires a bolt-cutter. The weave of the wire provides nice big holes through which you can fit your entire arm, important when you want to reach in to pick tomatoes.

When you get it home, just join the vertical ends, forming a round cage, and loop the wires to each other with a wrench -- you probably won't be able to bend the wire ends by hand. HEAVY METAL -- A lecture on heavy- metal contamination in urban gardens and how it affects plants and vegetables will be presented Tuesday by Dr. James Preer. The program, sponsored by Garden Resources of Washington (GROW), will be held at 7:30 at 4200 Connecticut Avenue NW, UDC Building 44, Room 221. Free. For further information, call GROW at 234-6300. TRAPPING JOBS -- The Gypsy Moth Division of the Maryland Department of Agriculture is looking for college-age people to help in male-trapping surveys. It's paid, full-week work running from the last week of May through August. Call Betsy Handley at 301/271-7711..