'Contained' gardens have some advantages

Have you ever wanted a garden that would fit on a windowsill? Or one that you could rearrange at any time? If so, container, or pot, gardening is an option to consider. Using anything from the logical clay pot to perhaps a cut-down barrel or wooden crate, gardeners can create a small patch of color to touch up a dull wall, or a miniature plot to produce a variety of vegetables.

Joann Sowell and Judy Phillips, of the ''Get Potted'' gardening center here, note that ''the advantage of pot gardening is that you can have and enjoy plants wherever you want them, inside or out.'' Container gardens, they add, can be used to cover or disguise ugly places, or to accent and emphasize and decorate other spaces.

The following are some of their pointers for successful container gardening: The most important element is good potting soil. Tell your nurseryman what you want to plant and where. He will either have a mix of his own that is suitable, or will recommend a commercial mix and advise if you need to add any material to it.

Equally important is the provision of good drainage for the pot, so make enough holes in the bottom of each container.

Since proper watering is so tricky, they recommend that novices particularly consider spending about $15 for a moisture meter with a long probe that can reveal moisture conditions deep down in the pot. Roots at the bottom should never stay too dry or two wet for a long period. Soil in containers dries out much more quickly than ground soil, they point out, and so must be checked more regularly, and watered accordingly.

Light requirements of different plants are important to learn. Some can stand exposure to sun all day long; some like no sun at all. Again seek advice from your local nurseryman. Once you know these, group or cluster together those plants that have the same light requirements. When you plan plants for a terrace or patio always try to combine plants so that some things are evergreen the year round, then add seasonal color and bloom.

As for feeding or fertilizing a plant, it is good to remember that things growing in containers need to be fed on a more regular basis than things growing in the ground. Time-release fertilizers are recommended for those people who have little time to garden. But whatever the fertilizer used, read and follow instructions very carefully. Never use more fertilizer than is recommended. Never overdo fertilizing, but try to establish a regular feeding program for your plants that are in containers.

If you become aware that a plant has a bug or a blight, break off a piece and take it to your nurseryman and ask for his professional advice.

Remember that many plants have been, or can be, adapted to shady conditions. Impatiens and caladiums, among others, are favorite shade plants in the South particularly. Many sun-loving plants, too, will gradually adapt themselves to shade or dappled shade conditions, if given a little encouragement.