Somehow it would seem that people who like to mess with dirt and shovels and get into the natural frame of mind would be the last sort to have anything to do with computers. Exit impressions, enter practicality. To be simple about it, people use computers to save time. Dear Gardeners: Computers can not only save you time but give you higher yields and take the guesswork out of the backyard veggie business. Here's how it works: you tell Compugarden, a Silver Spring firm, what percentage of what plants you want to the size of your garden -- all this done on their handy check-off form. For $12.50 you get back two computer printouts -- one for warm season crops, the other for cool season plantings -- and a guide to the printouts. The printouts tell you where to plant each plant and what to plant between specific crops. For example, had you chosen 30 percent of your garden to be tomatoes and your garden was 14 feet by 22 feet, part of the printout would have told you to space the plants 24 inches apart, to buy exactly 17 plants, to consider bush lima beans, pole lima beans and eggplant as companion plants, and to place the little gems in the ground about May 10. It also would advise a narrow strip of basil between your tomatoes and your cucumbers and a narrow strip of nastrutiums between your tomatoes and your summer squash. You can observe all this in the nine graphic of your garden plot which is neatly outlined by the computer. A companion booklet ont only helps decipher the already decipherable printout but tells you exactly how to cultivate your plot to use the French intensive method -- essentially squeezing your plants so close together that they are leaf-tip-to-leaf-tip and nowhere is there room for weeds to grow. All of which seems to be the perfect blend between technology and the great outdoors.

Forms available at many garden centers or write to: Compugarden, 725 Richmond Ave., Silver Spring, Md. 20910.