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

Asters

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Pixabay
Botanical Name
Aster spp., Symphyotrichum spp.
Plant Type
Sun Exposure
Soil pH
Bloom Time
Flower Color
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How to Plant, Grow, and Care for Aster Flowers

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Aster flowers enliven the garden in late summer and early fall, when many blooms are fading. These native perennials are an essential late-season nectar source for our pollinators, too! Here’s how to grow asters in your garden.

About Asters

The aster is an upright flowering plant which grows 1 to 6 feet tall and its star-shaped flower heads range from purple to white to blue. This perennial is best planted in spring or fall.

The aster plant 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.

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. (You may find aster listed with the species name Aster or Symphyotrichum). Learn more about recommended varieties further down this page.

Planting

Asters grow and flower best in full sun. Some varieties will tolerate part shade but will have fewer flowers. 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

  • Asters are most often bought as a potted plant. The best time to plant young asters is in mid- to late spring. Look for asters in the perennial sections of your garden center for the best selection.
  • Full grown and blooming asters also can be found in garden centers in late summer for fall decoration. Plant them in pots or in the ground as soon as possible after purchase so they can get established.
  • Asters can be grown from seed, but germination can be uneven. If desired, plant seeds outside in the fall, or start them indoors in winter in flats and refrigerate them for 4 to 6 weeks to simulate winter dormancy. Seven to 8 weeks before planting, place the pots/flats in a sunny spot with a temperature of 60º to 62ºF. Transplant seedlings outside in mid- to late spring after the danger of frost has passed. (See local frost dates.)

How to Plant Asters

  • When planting young aster plants, 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.
  • Asters prefer areas with cool, moist summers, as well as cool nights, in sites with full to partial sun.
  • In warmer climates, they do not like the hot midday sun.
  • Give plants plenty of water at the time of planting.
  • Add mulch after planting to keep soil cool and prevent weeds.
Aster and monarch butterfly
Asters are highly attractive to pollinators, especially bees and butterflies.
Growing

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.

  • 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.
  • 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.
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.

Wit and Wisdom
  • Because of the asters’ late bloom time, they are sometimes called “Michaelmas daisies,” which refers to the holiday of the same name that occurs annually on September 29! 
  • Asters, one of September’s birth flowers, were once burned to ward off serpents.
  • The name “aster” comes from the Ancient Greek word for “star”—a reference to the plant’s star-shaped flowers.
Pests/Diseases

Susceptible to:

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