Perovskia atriplicifolia — Russian Sage
Perovskia is neither Russian nor sage; rather, it is native to southwestern and central Asia, Afghanistan to Tibet. It is a member of the Lamiaceae (mint) family, as are the true sages in the genus Salvia. It was probably first called sage because its foliage smells sage-like when crushed. In cultivation since the mid-1800's, it is botanically a subshrub, which means that it has woody lower stems and taller soft herbaceous tissue where flowers appear.
The foliage of Russian sage is gray-green, with small, finely toothed leaf edges and pale green stems that age quite attractively to silver-white in winter. The foliage is pleasingly but pungently scented when crushed or brushed against. Tall, long-blooming lavender-blue flower spikes lend a cool, airy cloud of color to the garden mid- to late summer. Even in winter, groups of the white bare stems stand out as an attractive and prominent feature. Its loose, open habit makes this perennial an effective filler in the back of a border or above low-growing plants. Wide sweeps will attract hordes of bees and butterflies, but deer do not bother it.
Use Russian sage as an individual plant or two in small areas, ranked in a row as a wide hedge, or in broad swaths to magnify its presence. It combines well with ornamental grasses and white or yellow-flowered perennials along with striking red or orange blooms.
Perovskia atriplicifolia is a bit of a rampant spreader by underground rhizomes after a few years. It grows 3-5 ft. tall, spreads fairly fast and becomes robust with more rather than less irrigation. Cultivars include 'Longin', which is a bit better-behaved than the plain species form with a more upright, formal growth habit. 'Blue Spires' grows to about 4 ft. with foot-long flower-heads from mid-summer into fall; 'Little Spire' is more compact to 2 ft. tall; and 'Filigran,' the sturdiest and most upright of any Perovskia has silvery, fine, lacy or filigreed leaves, as the cultivar name suggests.
Perovskia wants full sun and little water. It is quite drought tolerant and suffers when over-watered, but it must be irrigated regularly during the first growing season to establish a deep, extensive root system. It prefers relatively poor, well-drained soil, so fertilizing is unnecessary. Fertile soil will boost leggy growth and require support for tall stems to keep the plant tidy. Good drainage and aeration will enable it to survive through our wet winters and prevent root rot in saturated soil.
Wait until after the last frost in spring before pruning Perovskia, then cut back hard to basal shoots about 6 inches above the ground, always cutting just above pale green buds. New growth emerging on low, woody stems encourages a denser habit. If plants are not pruned hard enough, growth can become lax and droopy, particularly when they are young.
Hardy to the lowest temperatures we see in Sonoma County, Perovskia also seems to be fairly resistant to leaf pests and most diseases.