Learn how and when to plant asters—daisy-like flowers that enliven the garden in early fall when many summer blooms are fading. These native perennials are deer-resistant and also provide late-season nectar for our pollinators!
Asters are perennial flowers which bloom from late summer through fall. Growing 1 to 6 feet tall, depending on variety, these upright flowering plants bear cheerful star-shape flower heads that range in color from purple to white to blue.
Even though there are more than 600 aster species, the two most commonly encountered asters in the home gardening world are the New England aster(Symphyotrichum novae-angliae) and the New York aster(S. novi-belgii). Several years ago, the Aster genus was split into multiple genera. Aster now covers most European and Asian asters, while those native to North America now belong to Symphyotrichum.
A number of hybrid varieties are available in showy colors, yet “wild type” species native to your region are generally a wise choice for the ecologically-minded gardener, despite them not being quite as flashy as the cultivated varieties in some cases. Learn more about recommended varieties further down this page.
Aster is versatile: Depending on the height, it’s suitable for borders, rock gardens, or wildflower gardens. As well as being a valuable pollinator plant for bees and butterflies, its tasty seed heads are sought by cardinals, chickadees, finches, nuthatches, and many other seed eaters.
Asters prefer areas with cool, moist summers as well as cool nights, in sites with full to partial sun. In warmer climates, asters do not like the hot midday sun. Soil should be moist but well-drained, and loamy. Wet clay soil will lead to root rot and dry sandy soil will lead to plant wilt. Mix 2 to 3 inches of compost into the soil prior to planting.
When to Plant Asters
The best time to put young aster plants in the ground is in mid- to late spring after danger of frost has passed. (See local frost dates.)
Or, you can plant mature, potted asters when they become available at garden centers (typically, in the late summer or early fall).
Asters can be grown from seed, but germination can be uneven. If desired, plant seeds in the fall or start them indoors in the winter.
How to Plant Asters
When planting young aster plants outside in the spring, space them 1 to 3 feet apart, depending on the type and how large it’s expected to get.
Fully-grown asters, such as those available in late summer or early fall, should be planted about 3 feet apart.
If planting seeds, sow 1 inch deep in pots or flats and refrigerate them for 4 to 6 weeks to simulate winter dormancy. This cold period will kick-start germination.
Water well and spread mulch around the plants to keep the soil cool and prevent weeds.
Add a thin layer of compost (or a portion of balanced fertilizer) with a 2–inch layer of mulch around the plants every spring to encourage vigorous growth.
If less than 1 inch of rain falls per week in summer, water regularly. But beware. Many asters are sensitive to too much or too little moisture. They will lose their lower foliage or not flower well. Watch for stress and try a different watering method if your plants are losing flowers.
Stake the tall varieties in order to keep them from falling over.
Pinch or cut back asters by one-third once or twice in the early summer to promote bushier growth and more blooms. Don’t worry, they can take it!
In winter, cut back asters after the foliage has died, or leave them through the winter to add some off-season interest to your garden. Birds may munch on the seeds, too.
Note: Aster flowers that are allowed to mature fully may reseed themselves. The resulting asters may not bloom true to their parent. (In other words, you may not get the same color flowers that you originally planted!)
Divide every 2 to 3 years in the spring to maintain your plant’s vigor and flower quality.
The most common asters available in North America are the New England aster (Symphyotrichum novae-angliae) and the New York aster (Symphyotrichum novi-belgii). Both of these plants are native to North America and are great flowers for pollinators. We recommend planting a native species of aster over a non-native species when possible, so talk with your local Cooperative Extension or garden center about which species are best suited to your area. Look for varieties with disease resistance.
North American Asters
New England asters (S. novae-angliae): Varieties have a range of flower colors, from magenta to deep purple. They typically grow larger than New York asters, though some varieties are on the smaller side.
New York asters (S. novi-belgii): There are many, many varieties of New York asters available. Their flowers range from bright pink to bluish-purple and may be double, semi-double, or single.
Blue wood aster (S. cordifolium): Bushy with small, blue-to-white flowers.
Heath aster (S. ericoides): A low-growing ground cover (similar to creeping phlox) with small, white flowers.
Smooth aster (S. laeve): A tall, upright aster with small, lavender flowers.
Aromatic aster (S. oblongifolium): Multi-branched at base, stiff upright stems, with lavender or pink flowers.
Frikart’s aster (Aster x frikartii) ‘Mönch’: Hailing from Switzerland, this mid-sized aster has large, lilac-blue flowers.
Rhone aster (A. sedifolius) ‘Nanus’: This aster is known for its small, star-shaped, lilac-blue flowers and compact growth.