Try planting a rock wall with Texas character

By G. Owen Yost

The vast majority of rock or stone walls in the North Texas landscape look drab and plain. They?re little more than a straight pile of rocks that has the appearance of just being built yesterday. However, with just a touch of imagination you can make a wall look like it has been around for decades, no matter when it was actually built ? even if it hasn?t been built yet. Best of all, you can probably plant an existing wall with living "character" in less than a day. The "character" comes about by filling the crevices and joints between the rocks with good soil and a variety of drought-tolerant plants.

Keep in mind that I?m talking about a simple, low "retaining" wall ? the kind where the soil?s higher on one side than the other. Typically, this type of wall has no mortar sticking the rocks together. Instead it has a "batter" ? it angles back, roughly 30 degrees from vertical, so that it sort of leans on the soil. Each rock?s weight is supported by the rock below it, and groundwater can seep between the unmortared rocks.

In North Texas, several kinds of plants are well-adapted. Some are santolina, frogfruit, snapdragon vine, rock nettle, sedum, Virginia creeper and my personal favorite ? lantana. You could also go with several species of wildflowers. It?s possible to plant moss or lichens, but these will sometimes occur naturally. Some rocks will even come with this "growth" on them already. Since the best time of year to plant begins about mid-September, you?re in luck!

When choosing plants, choose ones with smallish leaves; the size of the leaves should be compatible with the size of the rocks that make up the wall. Small-leafed plants like mistflower and coreopsis seem to look best. You don?t want to have too many plants or too many varieties ? it?s a wall, not an arboretum, after all.

To give a wall that "been-there-forever" look, pack globs of loose, muddy soil into the cracks and joints by hand. The soil mixture should be saturated, and you might even want to poke it deeply with a stick to push the mud into small crevices, and to get rid of air spaces (don?t try for style points here ? you will get dirty). Some folks prefer to add globs of the soil as they build the wall, letting the weight of the rocks squish the mud into the joints.

The soil itself should be primarily good, native topsoil ? not much different from what?s found naturally in your area. Ideally, the planting pockets (and future roots) will open out into the soil on the back side of the wall. So make sure there?s good contact between new soil and existing soil. This will provide a source for a little extra moisture (to prevent the new soil from drying out rapidly), and gives roots extra room to grow.

Actually, the joints and crevices in a "dry-stack" rock wall are a healthy (although tiny) environment for plants, some of which may normally be difficult to grow in this area. Since rocks take a long, long time to alter their internal temperature, plants are kept warmer in the winter and cooler in the summer. The wall, and the soil behind it, also has a moderating effect on the plant?s environment ? it doesn?t dry out as readily, for example. The only drawback is that plants in walls may need a little extra water when we have a sustained, dry, super-hot spell like we just had.

You can add character plantings to an existing, unmortared rock retaining wall, but you?ll need to add a step. Often, the voids in existing walls have already been filled by trash, infertile soil sediment, or roots from nearby plantings. So, I suggest spending a little time getting rid of this stuff, as much as possible, with a leaf-blower or a jet of water from your hose, or both. In addition to the new void plantings, plant some plants at the top of the wall to cascade down its face. Lantana, Virginia creeper, portulaca and santolina are good choices. This will soften the wall?s appearance by obscuring sharp edges and cracks.

However you do it, and whatever you plant, the wise use of plants can hide evidence of man?s intrusion, and gives the wall a characteristic "aged" look instead of an amateurish, man-made, built-yesterday appearance.

Owen Yost is an area landscape architect specializing in designing low-maintenance landscapes while incorporating native plants with hardscape. He is a member of the American Society of Landscape Architects, Keep Denton Beautiful and the Native Plant Society of Texas. His Denton office is at 4516 Coyote Point; call 940-382-2099 or 940-383-9655 or e-mail him at Yost87@charter.net