Great gardeners have perennial need to improve

At its purest, gardening is about expressing yourself by using other life forms. Sometimes plants conform to your vision; often they do not. If your mental image of a planting design is blurry at its inception, its physical realization is even more hit or miss.

So when you have succeeded in growing a group of plants in a harmonious gathering after a few false starts, the impulse is to rest on your laurels.

But the best gardeners I know are never quite content with what they've done or with what they know. Maybe they are restless souls or just insatiably curious. Whatever drives them, their obsessiveness makes for gardens that are enriching, inspiring and of interest through the whole growing season.

I could do with a bit more of the mania myself and have vowed in this season of resolutions and new starts to be more adventurous. Much of this resolve has to do with overcoming preconceived notions of what will work in the hot, humid mid-Atlantic climate and what will struggle. (I was wrong about calendulas, which do quite nicely in the right location, and nasturtiums can be happy, too. I don't think, though, that I'll ever plant a tuberous begonia or willow-leaf pear in Washington.)

I am resolved to try at least three new perennials in the season ahead.

Eryngium, or sea holly, is a stunning architectural plant - an electric blue, 3-foot candelabra of globes with a collar of spiky bracts. You see them as dramatic plants in the flower borders of northern Europe, often varieties of a species named Eryngium giganteum. They don't like the heat of our summers, and they lose their intensity of color as a result.

The one to pick here, my friends tell me, is E. planum. Named varieties have been developed for their more lively blue coloration, including Blue Cap (Blaukappe), Blue Glitter and, among varieties growing to just 18 inches, Blue Dwarf and Blue Diamond. Here's the rub: The sea holly is not a plant for a bed of heavy clay, or much shade. It is related to that other lover of dry environments and lean soil, the Queen Anne's lace.

Eryngium needs a bright, open site with free-draining soil, especially in winter, when its dormant crown needs to stay dry. Your landscaper's blanket of mulch would be deathly.

The openness and vivid structure of eryngiums may make them hard to place, and once you put them in a spot, they won't gladly move as an iris might. But if you have a sunny, dry site, they would be neat to use with, say, agastaches, salvias, goldenrods, butterfly weed and small to medium grasses.

There are native species of sea holly, but the most popular, E. yuccifolium, is a large and rather coarse-looking plant with greenish-white blooms. It would work nicely, I suppose, in a wildflower meadow garden.

And speaking of sunny, dry sites, my second pick is the Texas red yucca, which isn't strictly a yucca but is closely related. The yucca most people know here is the late-spring-flowering Yucca filamentosa, or Adam's Needle. Tall flower spikes, up to six feet, arise from a clump of spiky evergreen leaves. Some people dislike it for its sharply pointed leaves, but I just find it ungainly and awkward, perhaps because I rarely see it used effectively with other plants.

The Texas red yucca is smaller and more refined. Even better, the coral-red blooms are delicate but profuse and their flowering stems appear in late June and keep going until October. Friends who grow it say it is an absolute magnet for hummingbirds. Botanically, it is Hesperaloe parviflora, and several garden varieties have been introduced. High Country Gardens sells one named Straight Up Red, developed for its robust flowering.

If your garden has the opposite problem - damp soil - my third choice may be for you. Monarda, or bee balm, as a mint relative, doesn't like boggy conditions but needs even moisture. If the weather turns dry and the plant doesn't get watered, it will object by way of coating its leaves with powdery mildew. Think of a 3-year-old dressing up and then, when told the show's over, sprinkling herself with talcum powder.

Monarda is a lovely perennial - long flowering, showy without being glitzy, and another draw for hummingbirds. It is, as with coneflowers and liatris, one of the wildflowers at home in the garden. The common red plant is of the species Monarda didyma, which blooms in June and July. A second species, M. fistulosa, takes drier conditions and flowers a little later, with lavender-purple blooms that are not quite as eye-catching.

Fortunately, this plant has been the subject of a trial by the horticultural team at Mount Cuba Center near Wilmington, Delaware. After evaluating 40 selections over three years, the gardeners found 10 top performers. Four of them were rated as excellent in powdery mildew resistance, so my choice would have to be one of those.

Claire Grace is a variety of M. fistulosa selected for its better color, vigor and disease resistance. Violet Queen, another fistulosa type, was chosen for its exceptional mildew resistance. Its blooms seemed particularly attractive to bees.

Judith's Fancy Fuchsia is closer to the red-flowering species and was tested as the top disease-resistant variety among full-size monardas. The fourth, Grand Marshall, is a compact variety (28 inches) that, unlike other smaller varieties, still has a natural form. Surely this has a place in a breezy part of the small urban garden, even if its spelling of marshal isn't so grand.