Glaucous is Indispensable

The spell-checker on my computer doesn't like the term "glaucous." It politely suggests other words I might consider instead: "glucose," "gauchos," "glances."

Obviously, the person who generated the computer's dictionary wasn't a gardener, or "glaucous" would surely have been recognized as an indispensable term.

Glaucous plants have bluish-gray or bluish-green foliage. The color and texture of glaucous-leaved plants contrast gently with the shades of green around them, setting them off yet combining well with almost any other color. I couldn't compose a border without it.

The bluish tinge to glaucous foliage is the result of a waxy, or sometimes powdery, coating that covers the leaf surface. On a few plants the coating rubs off, but on most it's an integral part of the cuticle, or "skin," of the leaf.

These waxy cells make some leaves appear almost iridescent. Their function, however, is to protect the leaves from desiccation. That's why glaucous-leaved plants are commonly found in arid regions of the world, such as the Mediterranean and in the southwest United States.

Glaucous foliage is usually restful, not flashy or bold, unless, like Rudbeckia maxima, it has a presence so striking — some would say awkward — that it draws attention to itself for its habit alone.

The broad blue-gray leaves of Rudbeckia maxima fill space in the middle of the border quite handsomely. Then come the flowers. Single bare stalks, so thin they begin to flop almost immediately, shoot to 6 or 7 feet before they quit. At the top appear lonely yellow brown-eyed-Susan-like blooms, pretty, but wispy.

There are only two ways to abide the plant: In the back of the border (behind ornamental grasses or some other dense clump) faithfully staking each flower stem, or in the middle to front of the border and — you guessed it — cutting off the flowers.

I've tried growing Rudbeckia maxima both ways and prefer the latter. The glaucous foliage, in this case, is more appealing than the spot of color the plant ultimately delivers.

Meadowrue (Thalictrum spp.) is a gentle plant, as delicate and feminine at 2 feet (T. aquilegifolium) as she is at 6 feet (T. rochebrunianum 'Lavender Mist'). Softly scalloped blue-green leaves are best used "en masse" — at least three or four together in a drift — so the ladylike foliage isn't lost among bolder, more colorful plants.

I recommend, with caution, one of the most handsome, most intensely blue-gray plants available: Ruta graveolens, known simply as 'rue.' One nursery near me won't stock it anymore, after an employee developed a terrible rash by touching it.

Having been warned long ago this could happen — and not having young children to protect — I plant it anyway. The danger is in the sap (only hypersensitive people react to the leaves), so I wear long sleeves and gloves when working around it.

For me, the benefits outweigh the danger. Rue thrives in a hot dry spot in my garden.

Augment distinctive habit and texture with sultry blue-gray foliage, and ornamental grasses fill an important architectural void. Blue oat grass (Helictotrichon sempervirens) set the standard for many years, although the new 'Sapphire' is just a smidgen bluer.

Still, I prefer our native switch grass (Panicum virgatum), which out-performs both blue oat grass and blue fescue in my heavy clay soil. Fortunately, I have the space to accommodate this statuesque beauty, which can easily reach 4 feet. Look for 'Heavy Metal' and 'Dallas Blues' if you share the same challenge and want the bluest foliage possible.

Special enough to stand alone anywhere in a sunny garden is Rosa glauca (formerly Rosa rubrifolia). Smoky leaves are accented by maroon-tinged stems, and, briefly each spring, the gorgeous foliage is sprinkled with elegant single pink blossoms.

Rock gardens provide multiple opportunities for glaucous foliage. At home among the boulders is 'Cape Blanco' sedum (S. spathulifolium 'Cape Blanco'), along with the trailing stems of Euphorbia myrsinites (be sure to deadhead this one to prevent seedlings from overtaking the garden).

At the end of my rock garden, in a place of honor, is a very blue dwarf blue spruce, its glaucous needles a handsome foil for the creeping plants around it. A bolder gardener may have used yucca instead — 'Blue Sword' would be a good choice. Corydalis lutea scampers unchecked among the rock crevices in the stone wall that supports the rock garden.

Lindsay Bond Totten, a horticulturist, writes about gardening for Scripps Howard News Service.