MANY FAMILIES had vegetable gardens last year for the first time. Many more are expected this year. The 1982 season is about to begin for them in this area. Any day now, when the weather is suitable and the soil not too wet, digging can start preparatory to planting.

According to University of Maryland specialists, seed of spinach can be planted outdoors about March 10, onion sets and seed, plants of cabbage, seed of garlic and peas about March 15, roots of asparagus, seed of chives, potatoes, radishes, turnips and watercress about March 20 (See Planting Chart for Vegetables on Page 2).

To determine if the soil is dry enough to work, squeeze a handful tightly into a ball and then break it apart with your fingers. If it crumbles, it can be worked; if it cannot readily be broken up, it is too wet.

According to research botanists, there is no specific optimum temperature for seed germination. Usually the temperature of the top six inches of soil is warmer than the air above it in all seasons, winter as well as spring, summer and autumn. But the subsoil (12 inches or more down) while warmer in autumn and winter, is cooler in spring and summer.

The vegetable garden should be where it gets direct sunlight with no obstructing trees, shrubs or buildings. If sunlight reaches the garden no more than six hours a day, tomatoes, eggplant, peppers and lima beans will not do well. Leafy crops such as lettuce, mustard, collards, spinach, chard and kale can tolerate some shade.

Many soils in this area are quite acid and of heavy clay. They are slow to dry out in the spring and if cultivated while wet become hard and compact and neither air nor moisture can penetrate them. This condition is by no means hopeless. Adding lime and organic matter can help a lot.

A 2- to 3-inch layer of organic matter spread over the ground, along with some lime, will get you off to a good start. Use about 1 pound of ground limestone for 10 square feet and mix it and the organic matter with the top six to nine inches of soil.

By all means plant Sugar Snap peas, a 1979 All-America Gold Medal Selection, about the 15th, seed should be plentiful this year.

They are nutritious and filling but not as high in total carbohydrates and fats as green-shelled peas. The crunchy pods contribute fiber, vitamins and some carbohydrates.

If you cook them, don't overdo it; lightly steam or stir fry in oil to retain a hint of crispness. Overcooking will make pods come apart. They are easy to freeze but cannot be canned. The high temperature in canning destroys the structure of pods. Plants are resistant to common pea wilt. They have been reported to recover from frost as low as 20 degrees farenheit.

Q. How reliable are the meters used to determine soil acidity?

A. Those that cost $50 or less are not considered very reliable, those in the $150 to $250 range are reliable if used properly. However, knowing the acidity of your soil does not tell you how much lime to use. Your best bet is to send soil samples to your state university soil testing laboratory.

Q. Is it possible to spread diseases by composting old tomato vines and tree leaves that have been infected?

A. In the process of decomposition, temperatures rise to a point that usually destroys the disease producing organisms, also certain disease producing organisms such as viruses can only live on living plant material. However, if decomposition is not complete, the diseased material is hazardous.

Q. I'd like to increase my number of philodendrons. Is it best to get seed or take cuttings?

A. Many house plants, particularly tropical foliage plants, do not bloom or produce seed. They usually root well from cuttings 4 to 6 inches long, taken from healthy plants.