Late summer and early fall can sometimes be ho-hum times for flower gardeners (not to mention for pollinators who depend on flowers for survival). The riotous flush of summer blooms may be at an end, but that doesn't mean you have to say goodbye to flowers until next spring. But fear not, there's a great way to add flower color to your fall garden: asters!
Growing Asters in Your Garden
Asters are perennial to USDA Hardiness Zone 3 and provide both that wonderful pop of autumn color and late-season food for pollinators. They're easy to care for, and with more than 600 varieties, in a vast array of styles, colors, and sizes, you'll be sure to find something that will work perfectly in your garden.
Where to Plant Asters: Light and Soil Requirements
Asters thrive in full sun and loamy, well-drained soil. They will tolerate a bit of shade, but they won't bloom nearly as robustly. Depending on variety, asters should be spaced one to four feet apart at planting. Taller varieties might need to be staked to keep them from flopping over, so that's something to keep in mind as you're planning your garden and choosing varieties.
In northern zones, asters can be planted anytime from spring until early fall. In the south, where temperatures might stress plants more, they're best planted in spring or fall. Asters are fast-growing perennials, and will put on quite a bit of growth and bloom in their first fall after planting if they're planted in spring. If you plant in fall, expect lots of growth the following year and plenty of blooms that fall.
Watering and Fertilizing
Newly planted asters will need to be watered regularly while they're getting established in the garden. Water mature plantings of asters whenever they've received less than an inch per week of rainfall. Drought-stressed asters will have stunted growth and diminished blooms, so it's important to keep them well-watered during droughts.
Asters don't need much in terms of fertilizer. Side-dress the plants with a layer of fresh compost each spring, then apply mulch, and they'll be perfectly happy all season long.
For bushier growth and more blooms, it's a good idea to pinch aster plants back once or twice in early summer. The last pinching should be around the 4th of July. That will allow the plant to grow and form buds with plenty of time to bloom.
In fall, after the foliage has yellowed, trim the stems down to about two inches above the soil.
Aster Pests and Diseases
Asters are generally pretty easy to care for and free of pest and disease issues. However, there are a couple of common issues to watch out for.
Powdery Mildew: This is far and away the most common issue gardeners have when growing asters. This fungal disease starts out as a white, powdery, dusty-looking coating on the leaves. Eventually, the leaves will yellow, shrivel, and die, which weakens the plant and can prevent it from blooming. In really serious cases of it, the plant might die completely.
The easiest way to avoid powdery mildew is to make sure you're spacing your aster plants properly so they get good air flow. Avoid watering the leaves; water only at ground level. And if powdery mildew does show up, treat it with a commercial or homemade spray as soon as possible. If you find that your plants have powdery mildew a lot, look for mildew-resistant varieties, such as 'Blue Lake' or 'Winston Churchill.'
Aphids: These tiny, sap-sucking insects can weaken the plant. Look for them along stems and on the undersides of leaves. They can usually be dislodged with a spray of water from the hose, or apply insecticidal soap to get rid of them.
Slugs and snails: If you have a damp location, slugs and snails might make a meal of your asters. Pick off any you happen to spot, and consider surrounding the plant with diatomaceous earth or eggshells. The sharp texture dissuades these slimy pests from getting too close to your plants.
Beautiful Asters to Grow in Your Garden
There are so many options if you'd like to grow asters. You can find anything from diminutive asters for borders to tall, exuberant bloomers. Here are a few tried-and-true varieties to look for.
- White wood aster (A. divaricatus) is a native North American species that grows about 18 inches tall by 18 inches wide. Purplish-black stems grow in a distinct zig-zag pattern. Plants produce clouds of 1-inch flowers from midsummer through fall. This species is shade tolerant.
- Heath aster (A. ericoides) is a North American species that is also quite disease resistant. Plants range in height from 12 to 36 inches and have small, needle-like leaves. They produce masses of tiny flowers in the fall. 'Blue Star' is sky blue; 'Pink Haze' and 'Esther' are pink.
- Calico aster (A. laterifolius) is another North American native with good disease resistance. The foliage has an attractive reddish tinge throughout the summer. Plants reach about 30 inches and are often wider than they are tall. Clouds of tiny, starry flowers cover the plants in fall. 'Prince' is a popular cultivar with pinkish white flowers.
- Frikart's aster (A. x frikartii) is popular because of its long bloom period-from midsummer into fall. Flowers are fragrant and make excellent cut flowers. Growing 24 to 36 inches tall, these asters are very resistant to powdery mildew. 'Monch' and 'Wunder von Stafa' are the most popular cultivars and both have lavender-blue flowers.
- Bigleaf aster (A. macrophylla) is a woodland wildflower that prefers partial shade. It is sometimes grown as a groundcover. Plants form mounds of large, basal leaves. One-inch flowers appear in fall.
- New England aster (A. novae-angliae) is a much-hybridized North American species that grows 18 to 48 inches high and spreads 24 to 48 inches. Flowers have 1½- to 2- inch wide heads and are good as cut flowers. Cultivars include 'Alma Potschke', which grows to 36 inches high with salmon rose flowers; 'Hella Lacy', which grows to 42 inches with royal purple flowers; and 'Purple Dome', a compact, 18-inch plant with deep purple flowers.
- New York aster (A. novi-belgii) is another North American species offering many selections ranging from 12 to 48 inches high by 24 to 48 inches tall. The flower heads are usually just 1 to 1½ inches wide and the leaves are much narrower than those of New England aster. New York asters tend to be more susceptible to powdery mildew and wilt and are not as good for cutting. Some selections include 'Fellowship', which bears deep pink 3-inch blooms; and 'Bonningdale White', which bears white flowers on 48-inch tall plants. Low-growing selections include lavender-blooming 'Professor Anton Kippenburg' and white-flowered 'Niobe'.
- Tatarian aster (A. tataricus) is a tough plant that can withstand drought. A giant in the garden, the species can grow 5 to 8 feet tall, but seldom needs staking. Lavender flowers appear in mid to late fall. 'Jindai' is a cultivar that only grows 4 to 5 feet tall. Plant it at the back of the border to hide its barren lower stems.
Good Companions for Asters
Asters grow especially well with certain plants.
- Plant tall varieties in the back of the garden with other perennials such as Bugbane (Cimicifuga), black-eyed Susans (Rudbeckia), coneflowers (Echinacea), and ornamental grasses.
- More compact varieties work well with chrysanthemums and daylilies.
- Varieties that tolerate shade look great among native wildflowers and ferns.
Fall Color and Happy Pollinators
Asters provide much-needed color in the fall garden, all while attracting butterflies and other pollinators. Whether you grow them in a container or as part of a large perennial border, asters are a beautiful, easy-care perennial for your garden.