Yarrow. Calistoga is a fine, silver-gray foliaged selection of a classic California perennial and we considered this one of the best yarrows we grow. Collected by Phil Van Soelen from the rugged Palisades above the Napa Valley, it is a durable, heat tolerant cultivar with 12 to 18 inch tall spikes of clear white flowers from spring to fall. The handsome foliage provides excellent contrast in meadows, perennial borders, and rock gardens. It can also be mixed with other yarrows as a small scale lawn substitute. For best results plant in full sun and well drained soils. Hardy to 10F.