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Asters: How to Plant, Grow, and Care for Aster Flowers | The Old Farmer's Almanac

How to Grow Asters: The Compete Aster Flower Guide

purple aster flowers in a garden
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Pixabay
Botanical Name
Aster spp., Symphyotrichum spp.
Plant Type
Sun Exposure
Soil pH
Bloom Time
Flower Color
Hardiness Zone
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Planting, Growing, and Caring for Asters

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Asters enliven the garden in late summer and early fall when many flower blooms are fading—providing a late-season treat for the monarch butterfly, too! Plant these deer-resistant native perennials in midspring to keep the color going. Learn all about planting, growing, and caring for asters.

About Asters

Cold-hardy perennials with daisy-like flowers, aster flowers are the pollinator stars of the garden from late summer through fall. Growing 1 to 6 feet tall, depending on variety, these upright flowering plants bear cheerful star-shaped flower heads ranging from purple to white to blue.

Even though there are more than 600 aster species, the two most commonly encountered asters in home gardening 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 belong to Symphyotrichum.

Some 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.

Planting

Asters prefer areas with cool, moist summers and 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 before planting. 

When to Plant Asters

  • The best time to put young aster plants in the ground is in mid-to-late spring after the danger of frost has passed. (See local frost dates.)
  • Or, you can plant mature, potted asters when 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 they’re 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.
Aster and monarch butterfly
Asters are highly attractive to pollinators, especially bees and butterflies.
Growing
  • 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 weekly 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 lose flowers.
  • Stake the tall varieties 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 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 you planted initially!)
  • Divide every 2 to 3 years in the spring to maintain your plant’s vigor and flower quality.
Harvesting

Cut asters for flower arrangements when blooms are just beginning to open. Vase life is 5 to 10 days.

Asters have side shoots, which will continue to develop. These can be cut for indoor arrangements once they are the size you like.

Learn more about keeping cut flowers fresh.

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Wit and Wisdom
  • The name “aster” comes from the Ancient Greek word for “star”—a reference to the plant’s star-shaped flowers.
  • Asters are called “Michaelmas daisies” because they bloom around September 29, the ancient feast day of St. Michael, and a “quarter day,” marking the transition to autumn.
  • Asters, one of September’s birth flowers, were once burned to ward off serpents.
Pests/Diseases

Diseases: aster yellows; Botrytis blight; leaf spot, fungal; powdery mildewrust; rot, Rhizoctonia root and stem, white smut, Fusarium wilt, Verticillium wilt.
Pestsaphids, foliar nematodes, slugs and snails, Tarsonemid mites.

About The Author

Catherine Boeckmann

Catherine Boeckmann loves nature, stargazing, and gardening so it’s not surprising that she and The Old Farmer’s Almanac found each other. She leads digital content for the Almanac website, and is also a certified master gardener in the state of Indiana. Read More from Catherine Boeckmann

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