Growing Asters

How to Plant, Grow, and Care for Aster Flowers

Aster Flowers
Pixabay

Asters are daisy-like perennials with starry-shaped flower heads. They bring delightful color to the garden in late summer and autumn when many of your other summer blooms may be fading.

There are many species and varieties of asters, so the plant’s height can range from 8 inches to 8 feet, depending on the type. You can find an aster for almost any garden at garden centers in autumn!

The plant can be used in many places, such as in borders, rock gardens, or wildflower gardens. Asters also attract bees and butterflies, providing the pollinators with an important late-season supply of nectar.

Planting

Choosing and Preparing a Planting Site

  • Asters prefer climates with cool, moist summers—especially cool night temperatures. In warmer climates, plant asters in areas that avoid the hot mid-day sun.
  • Select a site with full to partial sun.
  • Soil should be moist but well-drained, and loamy.
  • Mix compost into the soil prior to planting. (Learn more about soil amendments and preparing soil for planting.)

Planting Asters

  • While asters can be grown from seed, germination can be uneven. You can start the seeds indoors during the winter by sowing seeds in pots or flats and keeping them in the refrigerator for 4 to 6 weeks to simulate winter dormancy. Sow seeds one inch deep. After 4 to 6 weeks, put the seeds in a sunny spot in your home. Plant outside after the danger of frost has passed. (See local frost dates.)
  • The best time to plant young asters is in mid- to late spring. Fully-grown, potted asters may be planted as soon as they become available in your area.
  • Space asters 1 to 3 feet apart, depending on the type and how large it’s expected to get.
  • Give plants plenty of water at the time of planting.
  • Add mulch after planting to keep soil cool and prevent weeds.

Aster monarch butterfly
Asters are highly attractive to pollinators, especially bees and butterflies.

Care

How to Grow Asters

  • 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 you receive less than 1 inch of rain a week, remember to water your plants regularly during the summer. However, many asters are moisture-sensitive; if your plants have too much moisture or too little moisture, they will often lose their lower foliage or not flower well. Keep an eye out for any stressed plants 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 back asters once or twice in the early summer to promote bushier growth and more blooms. Don’t worry, they can take it!
  • Cut asters back in winter after the foliage has died, or leave them through the winter to add some off-season interest to your garden.
    • Note: Aster flowers that are allowed to mature fully may reseed themselves, but resulting asters may not bloom true.
  • Divide every 2 to 3 years in the spring to maintain your plant’s vigor and flower quality.

Pests/Diseases

Susceptible to:

Harvest/Storage

Recommended Varieties

Wit & Wisdom

  • 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.
  • Thanks to the aster’s late bloom time, they are sometimes called “Michaelmas daisies.” Michaelmas is a holiday that occurs annually on September 29.

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Growing Asters

Botanical Name

Astereae

Plant Type Flower
Sun Exposure Full Sun, Part Sun
Soil Type Loamy
Soil pH Varies
Bloom Time Summer, Fall
Flower Color Blue, Pink, Purple, Red, White
Hardiness Zones 3, 4, 5, 6, 7, 8
Special Features Attracts Butterflies