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Let's plant a stone wall.

If only that were as simple as dropping a row of pebbles in the ground, stepping back, and waiting a few weeks or months for a wall to appear. But, of course, what I mean is to grow plants in a stone wall.

The nooks and crannies in any unmortared stone wall cry out for a bit of decoration. So much so that, without any helping hand, plants — too often weeds — frequently insinuate themselves into such walls here and there.

Stone walls do a great job of defining the landscape with their mass and lines; plants soften and decorate these walls.

CLIMATE CHANGE

Nooks and crannies in a stone wall can have microclimates quite different from the rest of your yard. For one thing, the soil in the wall usually drains off water extremely well. And temperatures are a bit different, the stone itself shading plant roots but absorbing and retaining heat to modulate temperature swings in the air nearby.

Microclimates vary, depending on a wall's exposure. North and east walls stay cool even in summer, while south and west walls bake.

WALLS ARE A GREAT BACKGROUND

The hard part is building a wall; the easy part is finding plants for it.

The best plants for walls are those that enjoy dryish soils.

As far as looks, the best wall plants are those with relatively small leaves and flowers.

And if the plants trail or drape, so much the better; foliage and flowers can drip like water from planted crevices.

The neutral grays and browns of stones provide ideal backdrops for setting off any color flower. A list of wall plants might include lavender, sea pink, lavender-flowered aubrietia, pink or white maiden pink, and purple flowered thyme.

A couple of natives that should do as well in built walls as they do in natural rock crevices are Dutchman's breeches and wild columbine. Both are dainty plants with flowers that call for the close, individual attention they'll get poking from a wall.

With some plants, it is their leaves, rather than their flowers, that earn them a backdrop of stone. An obvious choice here is hens-and-chicks; its fat whorls of succulent leaves multiply to tightly pack any cranny into which it is planted. Rock cress not only has downy leaves, but is covered with fragrant white flowers in early summer.

WALL CONTROL

Some plants that self-seed too aggressively "on the flat" are kept suitably in tow on a wall.

Chamomile — although lovely with its ferny, lime green foliage and cheery white daisy flowers — is one such plant, as is forget-me-not, an especially fecund annual. Snow-in-summer is a perennial that does not self-seed, but quickly blankets the ground with its creeping stems, which lope down from nook to nook in a stone wall.

Walls pretty much take care of the plants they house, but the plants do need occasional tidying. Most of the plants mentioned look better if they're cut back after a flush of flowers. This cutting not only keeps them more compact, but sometimes encourages another flush of blossoms.

Another point of maintenance is the base of the wall. Sure, you could weed-whip the grass that presses up against the stones, but you can avoid this by planting the base of the wall, too. How about a thick stand of daylilies or oriental poppies there?

Copyright 2009 The Associated Press.

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These walls were made for planting