According to Gallup polls the number of Americans who are growing their own vegetables is, like inflation, going up. And even if you're not overly impressed by that $200 a year saving in food bills for a family of four which Derek Fell, director of the National Garden Bureau promises, a plot of land may provide other, less tangible rewards -- say, tomatoes that don't taste like plastic. Fryer and Simmons survey the ingenious (or is it desperate?) means people are using to get back to the good earth even if it's only a 5-by-8 minigarden or some pots and boxes on the fire escape. Or join one of the ""communal"" or ""neighborhood"" gardens which seem to be springing up in vacant lots in the heart of the city. The authors are sensible and specific with sound, clear advice on spading and tilling the soil for those who've never done it, fertilizers, pest control and how to plant and harvest the twenty or so vegetables which an average backyard garden (about 12-by-30 feet) can accommodate. They do not advise strictly ""organic"" methods but the use of ecologically balanced fertilizers and no poisons (they provide recipes) should assure strong healthy high-yield plants. And for when the crops ripen there are instructions on home canning and fermenting pickles and sauerkraut. An appendix gives a list of agencies and organizations to write to for help with everything from asparagus to zucchini. Bon appetit.