Santolina chamaecyparissus, commonly santolina, lavender cotton, or gray santolina, is a low, mounding evergreen sub-shrub native to the dry hillsides of the western Mediterranean, grown almost entirely for its dense, felted, silver-gray foliage — finely divided and aromatic, holding its color through the whole growing season. Button-like yellow flowers on wiry stems rise just above the foliage in midsummer; some gardeners shear them off to keep the mound reading as pure silver texture, while others let them stand for the contrast.
It needs full sun and lean, sharply drained soil — rich soil or regular water makes the mound loose and floppy rather than tight and compact, and wet winter soil is the most common cause of loss. It tolerates poor, rocky, and alkaline ground, heat, wind, and salt, making it a mainstay of gravel and dry Mediterranean-style gardens, where its low mounded habit works as edging, a knot-garden element, or filler between taller silver and purple companions. Shear the whole plant back hard by about a third in spring, once new growth shows — left unpruned it splits open and goes woody and bare in the center within a few years.
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.