IN THE GARDEN LOBELIA BRINGS PLENTY OF BLUE.

Byline: JOSHUA SISKIN

Everybody loves lobelia.

How can you resist it? Lobelia is a demure botanical wonder that grows into a tidy globe of dark blue, bell-shaped flowers. It does well in mixed flower beds, as an edging plant in perennial borders, and is probably the best plant you can find for hanging baskets and containers. It will not grow more than 8 inches tall.

One of lobelia's virtues is its slow growth rate. The petunia, for example, whose brilliant red, pink, blue and purple colors give it a unique presence, simply grows too fast to be of lasting value in a flowerpot or garden bed. Yes, you can - and really must - cut petunias back after three or four weeks of growth, but even then they will only grow for another month or so before becoming leggy beyond redemption.

Lobelia, by contrast, will hold up well for at least four months, and its good looks may persist for six months or beyond, depending on the weather. If it should stop flowering, cut it back by half and wait for rebloom.

Two notes of caution are in order for Valley gardeners regarding lobelia. First, it needs sun protection as temperatures warm; second, it requires above-average soil moisture. By planting it in partial sun, you can extend the life of lobelia in the summer garden. Although lobelia is most well-known for its dark, marine blue varieties, it is also available in light blue, white, violet and a recently introduced carmine.

An outstanding botanical relative of lobelia is the throatwort or blue lace flower (Trachelium caeruleum). This eminently garden-worthy and lightly fragrant plant has, for some inexplicable reason, been all but absent from the nursery trade. It certainly deserves wider recognition and use, owing to its lace-cap clusters of lavender florets and long bloom period. It grows no more than a compact 3 feet in height and, cut back in winter, will reliably return in the spring. The culture of blue lace is similar to that of lobelia, and it is cold-hardy as well. Blue lace is a favorite cut flower selection; its colors include many shades of blue, as well as purple, pink, red and white.

Still another lobelia cousin is the balloon flower (Platycodon grandiflorus), a perennial whose silky mauve-blue flower buds look like expanding balloons as they enlarge. Eventually, the buds open into pentagram-shaped blooms with five curved-up star points and flat bottoms. The balloon flower, too, is cold hardy and combines well with lobelia and blue lace in an all-blue flower bed.

Regarding these or any other flowering plants, there is one rule that cannot be repeated often enough: Fertilize before you plant. Plants look good in nurseries because they have been fertilized since birth. When you place them in your garden or in containers, plants used to a steady mineral feed may go into a funk if fertilizer is not immediately available to them.

Blue flowers come into favor as summer approaches because of the cooling ambience they provide. Other blue bloomers you might want to try would include Veronica species, with dense arrays of blue flower spires; Geranium 'Johnson Blue' and other true geranium cultivars, whose flowers and foliage are more delicate and understated than the coarser and flashier ivy and zonal geraniums; bluebeard (Caryopteris incana), whose ethereal blue inflorescences surround the stem; butterfly flower (Clerodendron ugadense), so-named because of its flowers' exact resemblance to porcelain blue butterflies, antennae included; and 'Blue Fortune' giant hyssop (Agastache), with robust flower spikes reaching nearly a foot in length.

TIP OF THE WEEK: One of the easiest to grow and most heavily blooming perennials is the Santa Barbara daisy (Erigeron karvinskianus). Try counting the number of flowers on a Santa Barbara daisy plant, and you will give up soon enough. Hundreds of daisies cover a single specimen, yet the plant reaches less than a foot high and spreads to no more than 2 feet around. It is a whimsical English-garden sort of plant, is water thrifty and is also a prime candidate for window boxes and balcony planters because of its pronounced spill-over tendencies. It may fade in the middle of summer but comes back strong in the fall.