How To Plant asters

General Introduction

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

  • 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.)
  • 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.

Care

  • 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.
  • 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

  • Powdery mildew
  • Rusts
  • White smut
  • Leaf spots
  • Stem cankers
  • Aphids
  • Tarsonemid mites
  • Slugs and snails
  • Nematodes

Harvest/Storage

  • Asters work well as cut flowers! Here’s how to cut and keep flowers fresh.

Recommended Varieties

  • 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.
  • 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.

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.

How To Plant asters

Botanical NameAstereae
Plant TypeFlower
Sun ExposureFull Sun, Part Sun
Soil TypeLoamy
Soil pHVaries
Bloom TimeSummer, Fall
Flower ColorBlue, Pink, Purple, Red, White
Hardiness Zones3, 4, 5, 6, 7, 8
Special FeaturesAttracts Butterflies

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