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There are many reasons for the existence of rock walls. Such a wall may be the means of retaining a steep embankment, or of disposing of surplus stones. A rock wall can form a handsome dividing line between property or sections of a property.

Whatever the reason, why not make them attractive? I have a friend who built a dry rock wall all the way across her back yard for no other purpose than to display flowering plants, shrubs and ferns.

Choosing Rock Wal Plants

In choosing plants for a rock wall, one may select many colors in plants that flower during many periods of the season. The most commonly used plant encountered in rock walls is Alyssum saxatile, popularly known as “basket of gold,” and its double flowered form which remains in bloom much longer.

This should be planted in full sun. Perhaps the next most commonly used is Arabis albida with wooly gray leaves and long sprays of white flowers. This also comes in a double flowered form as well as one in rose and in a white cushion type, Arabis Kellereri.

Our native columbine, Aquilegia canadensis, planted near the top of a wall will throw its seeds into the most minute crevices and produce many attractive miniature plants. In fact, most of the aquilegias will do this.

An especially attractive one is the fan columbine, botanically known as Aquilegia flabellata nano alba, which comes to us from Japan. It has blue-green leaves and bears its white flowers on eight to ten-inch stems in May and June. This may be used in either sun or light shade.

Androsace sarmentosa forms solid carpets of small silvery rosettes and from the center produces five-inch stems bearing rose-pink flowers in May. It may also be grown in full sun or half shade. This is perhaps the easiest of the androsaces, but there are others worth experimenting with. Also among the pink flowering plants, the armerias are worth trying. Armeria juniperifolia rosea and the white form Armeria juniperifolia are most useful.

Our native bleeding heart, Dicentra eximia, is an ideal wall plant. Place it near the top of the wall and it too will reseed in the most unexpected crevices of the wall and produce attractive plants. The white form is still scarce and expensive but get it at any cost.

Aubrietia deltoidea was made for the rock wall. This plant may be used in sun or part shade. Aubrietias may be had in many shades of mauve, purple and lavender and if you look long enough you may be able to find a pure white one. They are easy from seed or may be propagated in early fall from cuttings.

Everyone is acquainted with Phlox subulata, commonly called moss pink or mountain pink. This can be had in white, many shades of blue, pink and the variety `Timiskaming’ in red, if it can be found, is lovely.

Saponaria ocymoides is a favorite dry wall plant in pink on long trailing sterns and it is a long summer blooming plant. Plant this in full sun. The white form of it is equally attractive but seldom encountered in the trade.

Gypsophila repens is easy and permanent in a dry wall. It bears loose sprays of large white flowers on ascending stems. Gypsophila repens fratensis is a more compact grower with clear pink flowers over a long season.

Shady Rock Walls

For the shady side of the wall, Corydalis lutea with showy yellow flowers all during the summer on lacy foliage, is around six inches high. This is a true rock plant and seldom survives unless grown next to or beneath a rock. Cymbalaria pilosa is a neat creeper with soft wooly gray-green leaves bearing lavender flowers throughout the summer and it may be used in sun or light shade.

Most of the sedums will adapt themselves to rock wall culture, but my choice of the lot would be Sedum cauticolum, a dwarf species from Japan with very thick blue leaves and vivid red flowers in September and October.

We encounter Sedum sieboldii in almost every rock garden. It makes an ideal rock wall plant with brilliant pink flowers in September and October. Full sun is best but it can be grown in partial shade. Try Sedum spathulifolium, a native of our Rocky Mountains with large gray leaves and bright yellow flowers on three-inch stems.

In full sun the leaves take on a pinkish hue. It may also be grown in partial shade. These sedums will not take over the entire wall as some others will. They are what I call “well behaved” plants.

Of course, no dry wall would be complete without a variety of sempervivums (hens-and-chicks). The names are so badly mixed that I shall not attempt to name them. Either visit a dealer in rock garden plants and select those which appeal to you most, or ask, a reputable mail-order dealer to make a selection for you. The cultural requirements of sempervivums arc easily met in only a handful of soil.

There are certain ferns that thrive in rock walls. On the sunny side of the wall one may use Asplenium platyneuron, commonly called ebony spleenwort or Pellaea atropurpurea, our native purple stem cliffbrake. This and the former are usually found in rock limestone situations and unless your wall is of limestone, they should have a pinch of lime added to the soil.

On the shady side of the wall nothing is more attractive than Asplenium trichomanes, commonly called maidenhair spleenwort, which is another lime lover. Why not experiment with other ferns? You may find several that will adapt themselves to the dry wall.

If you now have a perpendicular dry wall and the stones are tightly cemented together, there are still a few things that could be used to overcome its drabness. Several types of clinging ivy are used for this purpose. We usually think of clematis vine as a climbing vine on a trellis or fence, however if you plant it at the top of the rock wall, it will hang down and provide a most attractive picture.

The large flowered Jackmanii hybrids come in white, red and several shades of blue and purple. There is also a very attractive juniper, variety Tar Harbor,’ which can be similarly used. Its foliage is steel blue and does not turn bronzy in winter as does the foliage of many of the other junipers.

Should you be invited to the home of a friend for dinner you would not choose the largest portions. This is a good rule to follow when you visit your nursery as well as when collecting from the wild. A small plant is more easily established than a large one that has passed its prime. When planting, avoid air pockets and plant firmly.

L Totten