Jack Frost need not end the harvest of vegetables from your garden. Some kinds are fairly hardy, can be planted now and the early winter months, and yield higher-quality crops than those of spring plantings.

Vegetables harvested in the fall may actually be better suited for canning and freezing than those grown earlier because they develop more slowly under fall growing conditions.

While not all vegetalbes planted in late summer or early fall will mature fully, most are absolutely delicious when young,

To increase the chance of your fall vegetables' reaching maturity, select those having the shortest number of days to maturity.

Equally important with summer vegetables or the fall vegetable garden is a constant and uniform supply of water, according to University of Maryland specialists. If you let your garden soil dry out, your vegetables will cease growing and many will have off flavors.

Here's how late you can start various vegetables in your garden in this area. Those with asterisks should be started from transplants. JULY 25: Swiss Chard.AUGUST 1: beets, brussel sprouts*, carrots, cauliflower* and rutabaga. August 5: Chinese cabbage and snap beans. August 10: collards, kale and kohlrabi. August 15: head lettuce. August 20: broccoli*, cabbage*, endive and mustard. SETEMBER 1: leaf lettuce turnips. SEPTEMBER 5: spinach. September 15: radishes.

Fall greens taste much better when picked at the right time and cooked while fresh, and they're especially valuable nutritionally since they supply important amounts of vitamin A, ascorbic acid and iron.

Pound for pound, spinach, kale and turnip greens contain many time more vitamin A than snap beans,sweet corn or green peppers. A pound of raw kale or mustard greens may contain twice the ascorbic acid found in a pound of oranges, but some of this will be lost in cooking.

Many gardeners plant a combination of turnip greens, mustard greens and kale. A mixture gives a good flavor to the greens by playing down the bitterness of mustard while enhancing the flavor of turnips and kale.

Peas fresh from the garden are a spring taste-treat. You can double the treat if you plant them again before August 5. Q: I pick my lettuce, put it in the refrigerator and in four or five days it's spoiled. What could be wrong with it? A: Research has shown that lettuce will keep for three weeks or longer if stored dry in a gas-tight container (instead of polyethylene bags) at a temperature of approximately 34*f. Keeping the lettuce dry prevents bacterial growth, and using a sharp knife to cut it lessens physical damage that can shorten shelf-life. Q: How soon can cabbage be picked to use? A: Cabbage can be harvested anytime after a firm head develops. When it reaches full maturity, bend it to the ground on one side to break part of the roots to prevent head splitting. Q: For many years I have had moss for a ground cover in my yard instead of grass. Last fall it started to turn brown and die. Is there anything I can do to help the moss live? A: The presence of moss is usually associated with low soil fertility, poor drainage, soil compaction, improper watering, too much shade or a combination of these factors. Reduced humidity, increased sunlight and other changes in the environment can cause moss to go bad. Using misting-spray or fog-producing nozzles to produce and maintain high humidity that mosses need for good growth without overwatering them may help save them, plus continuous shade. q: My geraniums growing outdoors are blooming fine but they get occasional yellow leaves. Is there a way to stop it? A: Yellow leaves on geraniums usually indicate root injury due to over-watering. They should be watered thoroughly when they are watered, and then they should not be watered again until the soil is quite dry.