The so-called small leaf salvias, Salvia greggii (autumn sage) and Salvia microphylla (mountain sage), are so similar in appearance they are often mistaken for each other, but there are subtle differences. Flowers are almost identical, but greggii has smaller leaves with smooth margins while those of microphylla are slightly larger with serrated margins and visible veins. Other more important differences should be considered when choosing a species for your garden.
Greggii tends to be a little smaller, in the 2- to 3-foot range. It tolerates our full sun a little better, needs less water and is more likely to continue blooming through the hottest part of summer. However, greggii grows from a single stalk, tends to become very woody over time and is best replaced periodically. Stems are also very brittle and break easily.
Microphylla is a little larger, 4 by 4 feet or more. It tolerates more shade and even prefers some afternoon shade. It also needs a little more water. Microphylla will often pause blooming mid-summer, then resume when temperatures fall. Rather than having a single trunk, microphylla is more clump forming, spreads slowly and can be divided from time to time. Stems are more flexible, making it a better choice for gardens with active children or pets.
For the best of both worlds, look for a greggii-microphylla hybrid. Salvia x jamensis is a naturally occurring hybrid discovered in an area of Mexico where the greggii and microphylla habitats converge. Breeders have developed many other hybrids, including the popular Elk, Heatwave and Mesa series salvias. All do well in our area in full sun or part shade. Most are in the 4-by-4-foot range. They resemble microphylla in having more flexible stems and greggii in blooming more consistently through the heat of summer.
Care is pretty much the same for all. Good drainage is a must. Plants will look best with regular water, but definitely don't over water. Deadheading is not needed, but plants can be trimmed throughout the season to shape and keep plants bushier. Reserve heavier pruning for late winter/early spring when plants can be cut back to healthy new growth 12 to 18 inches above the ground. Neither of these species likes to be cut completely to the ground, although microphylla might tolerate it. Feed with a top dressing of compost in spring and avoid high nitrogen fertilizers. It's frustrating, but garden centers, especially big box stores, will often label small leaf salvias as just Salvia, with or without a variety or cultivar name. So look at the plant closely and do some quick research to insure you're buying the best plant for your particular situation.