A TREE-RIPPENED peach is one of the finer things of life. only those who grow them or know someone who does are aware of its goodness. It must be picked at the right time. You can tell, not by squeezing it but by giving it a slight twist. It will come loose in your hand if it is ready.Put it in a cool place for 24 hours and then enjoy it. Perhaps many more gardeners will be growing peaches in the near future. Dr. Freddi Hammerschlag atUSDA's Beltsville (Md.) Agricultural Reasearch Center predicts that a new technique soon may produce fruit-bearing peach trees many times faster than currently possible.

Traditionally, peaches have been propagated by grafting, because peach seeds do not reproduce all the characteristics of parent trees. Peach cuttings from most varieties are very difficult to root. In grafting, buds from last year's growth (budwood) are grafted onto the stem of one of a few types of peaches produced from seed (rootstock). This procedure is costly and time-consuming.

By using micropropagation techniques, a tiny shoot from budwood can produce five to 10 shoots every six weeks. Then each new shoot can be used to produce many more shoots. The shoots are then encouraged to root and, after an adjustment period, are put into soil for shipment to growers.

In this way, many plants can be grown very quickly. And virus-free budwood will produce other disease-free plants.

Hammerschlag, a plant physiologist working in the Cell Culture and Nitrogen Fixation Laboratory, is now successfully growing peach shoots in sterile media. The peaches she grows in this way include the popular varieties Dixired, Jersey Queen, Redskin and Sunhigh. Her next step is to encourage root formation so these trees can be tested in the field.

Similar techniques have been used successfully for propagating many nonwoody plants on a commerical scale, such as strawberries, orchids and ferns. However, trees are more difficult to grow.

In cooperation with Dr. Ralph Sconza, SEA Appalachian Fruit Research Station, Kearneysville, W.Va., Hammerschlag is studying yield, vigor, tree size and genetic stability of micropropagated fruit trees compared with trees propagated by grafting.

The main application for micropropagation is to raise low-cost disease-free trees from shoots of virus-free budwood for high-density orchards of 500 to 700 per acre. She expects micropropagation will dramatically speed up the testing and release of new varieties of peaches.

Other factors that influence success are temperature and illumination. The optimum temperature for peaches has been found to be 70 to 75 degrees Fahrenheit, with light for 16 hours a day.

Q. Every year my sweet potatoes rot during January. How can I prevent it?

A. Most sweet potatoes rot during storage because of rough handling during harvest. Scarring and bruising not only detract from the appearance but allow germs to enter their flesh. Harvest your potatoes carefully, cure them promptly by keeping them at 85 degrees and 90 percent humidity for four to seven days and store them at 55 degrees Fahrenheitand never below 50 degrees.

Q. When do strawberries form their fruit buds?

A. In early fall. That is why it is important to fertilize them in early September.

Q. When onions are frozen, are they ruined?

A. After five consecutive nights of freezing temperatures at a University of Minnesota Experiment Station test plot, the research onions were frozen . It was thought they would get soft and watery. Instead they came out in good condition. Due to their high water content and large size, it takes a relatively long time to freeze them.

Q. I canned some beans and tomatoes this year for the first time, and now most of them are spoiled. What would cause it to go wrong?

A. Speed is a key element in producing good canned vegetables. Another ingredient is the use of garden produce that is free from disease and at the peak of condition. All produce should be ripe but not overmature. Tomatoes and other produce with a high acid content require only a boiling-water-bath canner, but pressure canners are needed for those which have a low acid content. Wipe jar lid clean to ensure a perfect seal to avoid bacterial contamination, and store in a cool, dark place.

Q. My gourds did fine until late summer when some of the vines started dying. When does one take the gourds off?

A. Your gourd vines probably were attacked by powdery mildew. The gourds usually are picked in early October. They shold be firm and resist when you press them with your fingernail.