FLIMBY: A must for fall gardens, asters are little powerhouses

This is another installment in our Flowers in My Back Yard series, dedicated to to blooming plants.

Like their name implies, asters are the little stars of the September garden.

Their individual flowers may not be that large or showy, but their masses of blooms create bursts of late-season color – and welcome nectar for bees and butterflies.

Asters may be the most important nectar plant we can grow to feed hungry pollinators in early fall when little else is coming into bloom. Butterflies naturally gravitate to asters (they have the right landing-platform shape), and several species use asters as host plants for their young.

Birds appreciate them, too; in late fall, songbirds feed on aster seed.

More reasons to plant asters: They’re tough and easy care; they can take a lot of abuse and still keep blooming. They tolerate hot and dry summers with little effort on the gardener’s part. (And they make a long-lasting cut flower, too.)

“Aster” is the ancient Greek word for “star,” a nod to the flower’s shape. Cousins to daisies and sunflowers, asters are an easy-to-recognize part of the sprawling Asteraceae family, which includes more than 32,000 species. Of those, the genus Aster had included more than 600 species originating from North America and Eurasia. Genetic studies in the 1990s reclassified most of the New World asters into other genera. (The Aster genus itself is now down to about 180 species, mostly low-growing perennials.)

Regardless of where they originated, asters and their hybrids have made themselves at home in California gardens. They were made to grow here; several species are native to our Central Valley and foothills. That includes the prolific Pacific or California aster (Symphyotrichum chilense, formerly Aster chilensis), which grows wild from Southern California to British Columbia.

Improved hybrids have tamed asters’ wilder instincts – they’re fast growing and can be fast spreading – to make them compact additions to our flower beds. Among the best are ‘Monch’ asters (Aster × frikartii); this variety blooms profusely with little lavender-hued daisy-like flowers while the plant stays compact. Another favorite hybrid: ‘Purple Dome’ asters (Symphyotrichum novae-angliae ‘Purple Dome’), a variety of New England aster that forms an attractive mound of dark purple blooms.

Ranging in color from white to deep purple with plenty of blues and pinks in between, most asters are perennials. Growing from underground rhizomes, they form ground-hugging mats of dark green foliage. They need heat to sprout and are often the last perennials to poke out of the ground in spring.

In late summer, they send up flower stems, usually under 2 feet tall. In most species, the stems are packed with flower buds that eventually open into masses of daisy-like blooms or little buttons of pastel petals.

Their timing is keyed by the length of days. As summer wanes, days get shorter – and that triggers their bloom cycle. They usually sprout their first flower stems in late July with blooms opening sometime in September.

That timing also helps migrating fall butterflies in need of nectar as well as hungry bees.

In the British Isles, the native aster is nicknamed “Michaelmas daisy” because its bright blue flowers reliably bloom in time for the Feast of Saint Michael and All Angels, traditionally held Sept. 29.

Aster care

Naturally resilient and drought tolerant, asters have one necessity; they can’t stand wet feet. They need good drainage, including in winter. Don’t plant them in a place where there will be standing water; their crown will rot.

That said, they will tolerate clay soil – as long as they’re not over-watered. Add some compost or other organic material before planting to improve drainage.

Asters can be transplanted in fall or spring. They prefer full sun (at least six hours a day), but will tolerate afternoon shade. In summer, water weekly for best and most consistent bloom.

After their blooms are spent and birds have finished picking over the seed, trim the flower stems back to the base.

Asters make a good addition to mixed perennial beds alongside coneflowers and black-eyed Susans as well as in the front of mixed flower borders. (I use them as a companion plant for roses.) They’ll also grow in containers. Another plus: They’re deer resistant.