Stachys byzantine (lamb’s ear), Plectranthus argentatus, and the lovely, silvery Salvia argentea all have hairy, sometimes velvety, leaves that beg to be touched or stroked. Ever wonder why?
The answer is self-protection. The hairs, or trichomes as they are more correctly called, are designed to keep the leaf cooler by reflecting infrared radiation. Conversely, in colder situations, the trichomes can help preserve heat. Eidleweiss, for instance, have trichomes to keep them warm during cold nights on high alpine slopes. That’s why, when grown in our more temperate gardens, the lovely grey foliage can turn green.
Most hairy plants are sun lovers for the simple reason that they need more light to accomplish photosynthesis.
A bonus to hairy-leaved plants is that they are unattractive to sucking insects and leafcutter bees. Deer also show an aversion to fuzzy leaves.