July brings serious garden pests, stifling heat, abundance of vegetables and flowers, and -- just when your plants need you most -- vacations. There are steps you can take to ensure that your garden will still be there when you come back from the beach.

The first rule is don't entrust the care and feeding of your garden to just anybody. If you enlist the aid of a neighbor while you're away, make sure he knows what he's doing. Too often the willing pal will say: "Oh, I'll take care of things for you if I get to pick whatever produces while you're gone." Ever wonder why he doesn't have a garden of his own? I remember one year when some dear friends took care of things for us while we were gone. They couldn't distinguish between pigweed and potatoes, elephant ears and eggplant; I came home to bare ground.

Spend a solid morning in the garden a day or two before your exodus. Weed as much as you can. Mulch where you see potential trouble -- dry or particularly weedy areas and water-loving cukes. Side-dress squash, cucumbers and any newly planted seedlings with compost. Water very well -- an hour in the morning and another in early evening. Pick anything that is even approaching maturity. Then, of course, you're stuck with all this produce right before you're ready to leave, but you're better off even composting mature vegetables than leaving them on the plants to age while you're gone. Frequent picking now will ensure a bountiful harvest when you get back. You surely can find someone who'll take this excess produce off your hands, if you don't have enough time to can it before you go.

Some judicious application of Sevin or rotenone may be necessary on plants that are being particularly hard-hit, since you won't be around to hand-pick bugs. Check squash for borers (look for a white, pulpy excretion at the base of the vine). Use a sharp knife to split the stem and extract the borer, which is quite an ugly little white beast with a black nose. Set Japanese-beetle traps if they have been harassing your garden. If there are a lot, the traps may fill up quickly, so you might want to put out a bunch. Japanese beetles have no regard for what they eat -- they love everything.

Don't try to start or set out seedlings or sow new beds before you go. They need supervision the first few weeks, and will die quickly if not watered. Mow the lawn close. Fertilize your roses and clip off all the blooms; this will stimulate new growth and blooms. Water new shrubs well, and anything else that you've put in recently. You never know how long it may be before it rains, and even if it does, well-watered plants won't suffer. Don't water your lawn, however, unless you're willing to give a really good soaking now and keep it up all summer. Lawns do all right during hot dry weather; they may brown slightly but the roots won't die. Uneven or shallow watering is counterproductive.

Enjoy your vacation, and you will come home to happy eating. FABULOUS FALL: Plan now for a fall garden. Take stock of your seed situation. You can plant virtually anything in August that you planted in the spring, except tomatoes, corn and late-maturing winter squash. Vegetables that mature in up to 70 days will do nicely. If you order seeds this weekend you'll get them in time for planting a fall garden. When you order, think about getting some vegetables that will winter over and give you early crops next spring. An excellent source is the Hastings catalogue, a Southern garden guide, which carries good varieties for Washington's hot, humid summers (Hastings, P.O. Box 4274, Atlanta, Georgia 30302; 404/524-8861).

I like to turn over part of my garden in late summer to something I've never tried before. This year I'll plant leeks for a spring crop. Incidentally, putting similar vegetables in the same area works fine within the same year. Rotate the following year.

TEATIME: An excellent way to get both water and nutrition to all flowers, shrubs, perennials and vegetables is the application of manure tea. Pick up a bag of dried sheep manure at the garden center, or cow manure if that's all they have, and mix water and a handful of manure until you get a solution about the color of ordinary tea.

You can make sunshine manure tea, leaving it out for several hours in the hot sun. When it gets to about the right color, pour the tea gently around plants. If the idea of handling dried manure bothers you, get a bottle of fish emulsion and follow the directions. Apply once a week, and you'll be amazed at how your plants grow. You can also use this formula on house plants.