Q:
I have a new stone retaining wall that looks pretty imposing in the landscape. I’m thinking of planting crevice plants to help it fit in more with the garden. The wall faces south, so it’s pretty toasty in summer. What plants would you recommend?
Mike Girvin, Newberg, OR
The crevices of a stone wall are perfect places to grow sedums, like this cascading evergreen Sedum spathulifolium.
Photo/Illustration: Jennifer Blume
A:
Barbara Ashmun, a contributing editor and garden designer from Portland, Oregon, responds: For a sunny site, trailing sedums would be an ideal choice, and there are plenty of cultivars to consider. For permanent backbone, try some evergreen varieties, for example Sedum spathulifolium ssp. pruinosum var. purpureum (USDA Hardiness Zones 5 to 9). Native to cliffsides of the coastal range,‑it’s a flat creeper that will hug the rocks with its frosty-purple, spoon-shaped leaves. S. spathulifolium ssp. pruinosum ‘Cape Blanco’ (Zones 5 to 9) has the same rounded, succulent foliage, but in pale silver-gray. Both have tiny yellow flowers in early summer.
Sedum spurium (Zones 4 to 9) also offers evergreen cover; the original species is green, with small leaves covering the stems and bright-pink flowers in summer. ‘Dragon’s Blood’ and ‘Fuldaglut’ flaunt deep-red foliage that would be riveting against stone.
I adore Sedum sieboldii (Zones 6 to 9) for its gray-green leaves edged with pink, a good match for its pink fall flowers. The lively yellow-green leaves of Sedum kamtschaticum (Zones 4 to 9), topped by yellow flowers in late summer, make a cheerful picture. And for those seeking variegation, Sedum kamtschaticum ‘Variegatum’, banded with cream, and Sedum sieboldii ‘Mediovariegatum’, highlighted with gold, are both excellent choices.
Sedums thrive in sunny places, but they will also manage well enough in partial shade. They’re among the easiest of perennials. Stick them in clay soil and they thrive, plant them in rocky places and they flourish. If you want them to grow quickly and heartily, mulch with a little mushroom compost. You can water them on the same schedule as your other hardy perennials or treat them with benign neglect, as their succulent leaves store water, making them drought-tolerant.
Propagating sedums is a snap. In the spring, dig around the outside of the mother plant with a trowel and pry away a few stems with roots on them. Cut back each stem, leaving just one or two pairs of leaves, and either pot it up or plant it directly in the ground. You can also root tip cuttings in a flat of damp sand. Simply cut off about 6 inches of the stem tip, strip off the lowest set of leaves, and cut the remaining upper leaves in half. Stick each cutting in damp sand, firming it in so that it’s snug, and in a few weeks your cuttings will have formed roots. To determine when the cuttings have enough roots to plant, tug on them lightly from time to time. When you feel resistance, the root system has established itself.
