Silene acaulis — moss campion — forms a dense, ground-hugging cushion of tiny evergreen leaves that can take decades to spread more than a foot across. It is native to arctic tundra and the highest, most exposed alpine slopes of the Rocky Mountains, Sierra Nevada, and Northeastern peaks, as well as the Arctic and high mountains of Europe and Asia. In early summer the whole cushion studs itself with small, five-petaled pink flowers held just above the foliage — a disproportionate amount of bloom for such a tight little plant.
It is essentially bulletproof against cold, tolerating temperatures well below -30°F, but struggles badly with heat, humidity, and wet winter soil — conditions common at lower, warmer elevations. Grow it in a scree bed, trough, or crevice garden with sharp drainage and full sun, and resist the urge to feed or baby it; lean, mineral soil close to its native habitat keeps the cushion tight instead of loose and rot-prone.
Root rot
Plants wilt, yellow, and stunt even in moist soil; lower stems and roots turn brown, soft, and mushy and the plant may collapse. Most common in heavy, wet, or poorly drained ground.
Improve drainage and stop overwatering, and never plant too deep. Lift and destroy badly affected plants along with the soil around the roots. Grow in raised or free-draining beds to prevent it returning.