The Perennial Matchmaker

You’ll hardly notice asters (Aster) for the first few months of the growing season, but once their flowers start opening, you’ll know why they’re considered the stars of the late-summer and fall garden. Most classic garden asters are still sold under the genus name Aster, but you may also see the North American species listed under their newer names, including Symphyotrichum and Eurybia. There are so many species, selections, and hybrids of asters to choose from, you can find at least one for just about any site.

Many excellent asters thrive in full sun and average to somewhat dry soil. Frikart’s aster (A. × frikartii) has bluish lavender flowers atop loose, 2- to 3-foot-tall clumps from midsummer into fall, for Zones 5 to 9. Bushy aster (A. dumosus [Symphyotrichum dumosum]) features purple-blue, pink, or white flowers on 1- to 2-foot-tall mounds from late summer to mid-fall, for Zones 4 to 8. Smooth aster (A. laevis [S. laeve]) sports light purple to blue flowers atop upright, 2- to 4-foot-tall stems in early to mid- or late fall, for Zones 3 to 8. And aromatic aster (A. oblongifolius [S. oblongifolium]) has purple to purple-blue flowers on dense, 2- to 3-foot-tall mounds in early to mid-fall, for Zones 4 to 9.

For average to moist sites in full sun, consider some of the many selections of New England aster (A. novae-angliae [S. novae-angliae]). Hardy in Zones 3 to 8, most grow somewhere between 3 and 6 feet tall and flower in early to mid-fall, primarily in shades of purple and pink.

For average, well-drained sites that get some shade, consider white wood aster (A. divaricatus [Eurybia divaricata]), with tiny white flowers on near-black, 1- to 2-foot-tall stems, or blue wood aster (A. cordifolius [S. cordifolium]), with tiny, light blue flowers on 2- to 3-foot-tall stems. Both form upright, loosely branched clumps that flower from late summer or early fall to mid-fall and can grow in Zones 3 to 8.

As a group, asters offer many tints and shades of purple, purple-blues, and pinks, as well as white. Their flowers have yellow to orange-yellow centers, which you can complement with yellow-flowered companions, such as perennial sunflowers (Helianthus), as well as leaves that turn yellow, like those of bluestars (Amsonia), purple moor grass (Molinia caerulea), and Siberian iris (Iris sibirica).

New England asters offer some particularly strong pinks, including ‘September Ruby’ and the even more intense ‘Alma Potschke’, and rich purples, as on ‘Purple Dome’. They can pair well with other bright pinks and purples, as well as oranges and yellows: Think of bold late-season bloomers, such as goldenrods (Solidago) and rudbeckias (Rudbeckia), for instance. If you aren’t comfortable putting bright colors right next to each other, separate them with the foliage of a warm-season ornamental grass, such as prairie dropseed (Sporobolus heterolepis) or switch grass (Panicum virgatum).

The various other pinks, purples, and purple-blues in the asters offer many more opportunities for late-season combos. They, too, work well with rudbeckias and other yellows, as well as with pinks, purples, blues, and peach-colored flowers and green, blue, gray, silver, and yellow- to cream-variegated foliage. White asters look great with all of those colors and with white-variegated leaves, like those of ‘Francee’ hosta and variegated obedient plant (Physostegia virginiana ‘Variegata’).

A Perfect Match

When I hear gardeners complain about the typical fall asters looking too “wild and weedy,” I like to recommend ‘October Skies’ aromatic aster as an alternative. It forms dense, neatly rounded mounds that look like tightly clipped shrubs, but with no pruning necessary. It’s terrific in front of loose, somewhat sprawly companions, such as ‘Brookside’ hardy geranium (Geranium) or ‘Full Moon’ coreopsis (Coreopsis), providing support without getting smothered itself.

Most asters have a mounded habit, with tightly or loosely branched clumps, but some—including most New England asters—are rather upright, with branching mostly along the upper half of the stems. Their leaves tend to be on the small and narrow side, giving the plants a fine texture. Overall, they aren’t particularly interesting for either shape or texture, except for aromatic aster, which naturally forms quite dense domes, 18 to 24 inches wide. To give your aster combinations some zip, include companions with contrasting features, such as a low, spreading habit or broad or spiky leaves, like those of bearded irises or yuccas (Yucca). Upright asters, in particular, benefit from having lower, mounded partners, such as hardy geraniums (Geranium), to cover their often-bare lower stems.

Flower-wise, asters are all fairly similar, with relatively small to tiny, daisy-form blooms that have very narrow petals. If you’d like some repetition, echo their shape with larger daisy-type flowers, like those of orange coneflower (R. fulgida), perennial sunflowers, or purple coneflower (Echinacea purpurea). Make sure you add some contrast, though, with companions that are spiky, such as fountain grasses (Pennisetum) and obedient plant (Physostegia virginiana); with plumed blooms, like those of flame grass (Miscanthus ‘Purpurascens’) and goldenrods (Solidago); or with broad, clustered flower heads, like those of Joe-Pye weeds (Eupatorium) and upright sedums (Sedum).

Frikart’s aster tends to be the earliest bloomer in this genus, possibly starting in early summer in southern gardens but in midsummer in most areas: just in time to fill the gap between the early and late show with other summer favorites, such as daylilies (Hemerocallis), Russian sage (Perovskia), showy stonecrop (S. spectabile), and summer phlox (Phlox paniculata).

Frikart’s aster continues into late summer, eventually joined by other asters for the late-season spectacle. Bushy aster is usually first, at the end of summer, with the others joining in at some point in early fall. Their bloom period overlaps with quite a few other perennials: earlier bloomers that are flowering again after a break, such as catmints (Nepeta) and coreopsis (Coreopsis); summer bloomers that are still producing new flowers, such as purple coneflower; and late-summer and fall bloomers, such as chrysanthemums, goldenrods, heleniums (Helenium), and Japanese anemones (Anemone). In shade, white wood and blue wood asters make charming co-stars for other late-flowering shade perennials, such as bugbanes (Cimicifuga) and toad lilies (Tricyrtis).

For additional companions, look beyond flowers to perennials and grasses with colorful leaves, as well as those whose foliage turns from green to other hues in fall. Try yellow to orange bluestars (Amsonia), deep red Bowman’s roots (Gillenia), golden to purple balloon flower (Platycodon grandiflorus), coppery little bluestem (Schizachyrium scoparium), and orangey prairie dropseed (Sporobolus heterolepis). And don’t forget the many dark seed heads of the fall season, such as the ball-shaped clusters of echinaceas (Echinacea) and rudbeckias and the spikes of Culver’s roots (Veronicastrum). Those seed heads, along with the dried stems and seed heads of ornamental grasses, join the lingering structure of woody-stemmed aromatic aster and New England aster to make a wonderful show well into winter.

With their abundance of small, daisy-form flowers, asters of all kinds are favorites with butterflies as well as bees and other beneficial insects. If you’d like to attract more of these creatures to your yard, pair your asters with other pollinator-friendly perennials, such as blazing stars (Liatris), goldenrods, oxeye (Heliopsis helianthoides), perennial sunflowers, and summer phlox.

Asters are native to many parts of the United States, so there’s little wonder that they look right at home in naturalistic gardens. (These natives also tend to self-sow freely, which is less of a problem in these casual settings.) Enjoy the sun lovers in meadow-style plantings with other native perennials and grasses, such as echinaceas, heleniums, ironweeds (Vernonia), Joe-Pye weeds, rudbeckias, and little bluestem.

The shade-tolerant white wood and blue wood asters are, not surprisingly, wonderful for woodland gardens, as a late-season follow-up to early-blooming native and nonnative companions, such as epimediums (Epimedium), foamflowers (Tiarella), hostas, and Solomon’s seals (Polygonatum)—all of which happen to have showy fall foliage color, too.

Though they generally don’t like constantly soggy soil, New England asters are well adapted to sites that are on the moist side, and they can tolerate short periods of flooding, so they’re well suited to sunny rain gardens. Pair them with other perennials that can thrive in those conditions, such as Culver’s root (Veronicastrum virginicum), rose mallow (Hibiscus moscheutos), switch grass, three-lobed coneflower (R. triloba), and turtleheads (Chelone).

Most asters are bushy or upright, but ‘Snow Flurry’ heath aster (A. ericoides) is distinctly different, with a low, spreading habit just 4 to 6 inches tall. It makes an out-of-the-ordinary, fall-flowering groundcover for sunny, average to dry sites in Zones 5 to 8. Let it mingle with other low-growers, such as creeping thymes (Thymus) and two-row sedum (Sedum spurium), on a slope or atop a retaining wall.

Delay the Display

A little pruning can work wonders on asters, delaying the flowers of Frikart’s aster (Aster × frikartii) to late summer and holding the others off for an additional few weeks so they can make a real end-of-the-season spectacle. (This is especially useful in warmer zones, where unpruned asters may be just about finished by the time fall actually arrives.) Pruning is also invaluable on the upright types, such as smooth aster (A. laevis) and the taller New England asters (A. novae-angliae), keeping them lower and bushier to minimize the chances of their sprawling. Trim lightly, removing just 1 to 2 inches from the tips, every few weeks from mid-spring to early July, or do one hard pruning sometime in early summer, cutting back the stems by about half their height at the time.

Bloom Buddies

Marvelous Matches for Flowering Combos

There’s no shortage of fantastic flowering companions for asters (Aster) in late summer to mid-fall. Here are some perennial partners to consider.

Combinations in full sun to light shade:

Catmints (Nepeta)

Chrysanthemums (Chrysanthemum)

Daylilies (Hemerocallis, reblooming types)

Echinaceas (Echinacea)

False aster (Boltonia asteroides)

Golden lace (Patrinia scabiosifolia)

Goldenrods (Solidago)

Heleniums (Helenium)

Japanese burnet (Sanguisorba tenuifolia)

Joe-Pye weeds (Eupatorium)

Lesser calamint (Calamintha nepetoides)

Monkshoods (Aconitum)

Montauk daisy (Nipponanthemum nipponicum)

Mountain fleeceflower (Persicaria amplexicaulis)

Obedient plant (Physostegia virginiana)

Perennial sunflowers (Helianthus)

Rudbeckias (Rudbeckia)

Sedums (Sedum, upright types)

Combinations in partial shade:

Blue lilyturf (Liriope muscari)

Bugbanes (Cimicifuga)

Hardy begonia (Begonia grandis)

Japanese anemones (Anemone)

Obedient plant (Physostegia virginiana)

Toad lilies (Tricyrtis)

Yellow waxbells (Kirengeshoma palmata)

Exploring More Options: Partners beyond Perennials

Asters are ideal companions for border-size, summer-flowering shrubs that also offer great fall color, such as ‘Hummingbird’ summersweet (Clethra alnifolia), which turns bright yellow; smokebushes (Cotinus), with their brilliant reds and oranges; and southern bush honeysuckle (Diervilla sessilifolia), with deep reds and muted tones of orange and yellow. Try ‘Tor’ birchleaf spirea (Spiraea betulifolia) to end the season with fiery reds accented with touches of orange and gold.

Add a touch of the unexpected to your autumn aster combinations with late-flowering bulbs, such as light purple fall crocus (Crocus speciosus) or pink or white colchicums (Colchicum) in sun and pink hardy cyclamen (such as Cyclamen hederifolium and C. purpurascens) in some shade. These little gems reach only 4 to 6 inches tall, so keep them close to the front of the border, paired with lower asters, such as aromatic aster (Aster oblongifolius), blue wood aster (A. cordifolius), bushy aster (A. dumosus), and ‘Purple Dome’ New England aster (A. novae-angliae).

Need some height to complement taller asters in your fall combinations? Many tall-growing tender perennials are at their peak from late summer to frost. Salvias (Salvia) are especially good for autumn color: Consider anise-scented sage (S. guaranitica), hybrid ‘Indigo Spires’, and rosebud sage (S. involucrata), to name just a few. Cannas, with their bold foliage and rich colors, are also excellent aster companions. And don’t forget dahlias, which produce an abundance of bloom as temperatures begin to cool in early fall.