No inducement ordinarily is required for me to journey to Longwood Gardens in Kennett Square, Pa., and the opening Feb. 14 of a special group of balcony gardens was an added enticement.

For apartment, condominium and townhouse dwellers, Longwood has created examples of gardens, replete with furnishings and innovative uses of plants. Set within Longwood's famous conservatories, the exhibit, which will remain on view for a year, offers ideas and information for all who garden in restricted space, from window boxes to balconies.

A trip to Longwood Gardens, on U.S. 1 near Philadelphia, is a one-day excursion from Washington. From time to time the exhibits will be replenished with new plants. The conservatories are open every day from 10 a.m. to 5 p.m. The entrance fee is $2 for adults, $1 for children ages 6 to 14 and free for those younger.

Five life-size balconies have been constructed to illustrate a variety of gardening-living situations. Entitled "Gardener's Balcony," "Dining 'al fresco'," "A Balcony For All Seasons," "City Form" and "Victorian Moods," each shows a different design based on structure, light, temperature and life-style of the occupant. Dimensions correspond to those ordinarily encountered in a apartment construction.

The "Gardener's Balcony" assumes that a gardener has a southern exposure, permitting intensive gardening the year round. This example shows how a balcony can be enclosed with lucite panels to function as a greenhouse in winter - light-weight and hinged, the panels can be installed in the fall and dismantled in spring. Work and storage space are included in the design. Seedlings an and potted plants illustrated an appropriate use of the balcony at the February opening date.

"Dining 'al fresco'" probably held the most appeal for me. This fresh-aid dining setting shows hoow an imaginative use of plants, furnishings, and home-made accessories enliven a simple balcony. Macrame hangers hold clay pots of ivy and ferns. Terra cotta drain tiles or flue liners cut to varying heights serve as pedestals for an assortment of potted plants. An unusual idea in this garden is the use of old fence post, hollowed out, filled with plants and set on the floor parallel to the railing.

"A Balcony for All Seasons" is an example of out-door gardening in containers. The 'Blue Rug' juniper in a hanging basket especially caught my eye. Two triangular, wooden floor planters in the outer corners, filled with hardy ground cover plants, are accented with a small flowering dogwood and a 'Bennett' Tsuga canadensis for year-round interest. Involvement with the great outdoors is indicated by the whimsical inclusion of a bird feeder.

"City Form" is the title of a pieceof abstract sculpture that is the focal point of this balcony. Plants and accessories were chosen to complement the sculpture. The Euphorbias especially constitute living sculpture. English ivy partially covers the balcony railing. Emphasis is on simplicity of design and repetition of plant types.

"Victorian Moods," the fifth balcony, was created by adding a wrought iron framing and railing from a Victorian house. It resembles the porch or veranda of an older home. Flagstone floor and cast iron furniture give it special character. Lush baskets of yellow abutilon and forget-me-nots were featured on opening day. Additional plantings of the same species with ferns and ivy, concentrated at the railings, allow room for people to enjoy the balcony.

A series of windowsell and window box gardens illustrate another aspect of apartment gardening, both indoor and outdoor. A collection of miniature geraniums and ivies on a windowsill suggested a kitchen setting. The plants in 3-inch pots were set on upended bricks at various heights, all arranged in a pebble tray, with an accompanying suggestion that the pots be shifted from one brick to another periodically to give equal light to all.

Another part of the exhibit is devoted to indoor gardeners' interest in use of fluorescent lights for growing and showing their plants. Included is a nandsome collection of foliage plants assembled in an east window where a new type of spotlight, ceiling mounted, supplements the natural light.

Nearby shelves show the uses of fluorescent tybes for display of plants or for growing seedlings or bringing other plants into flower.