How to Care for the Aster Flower

The aster flower is an attractive daisy like perennial. Coming in a range of colors, from white to purple, its star shaped blooms bring late summer and early fall color and interest to a garden.

The aster flower is also known as the Michaelmas daisy because it often blooms around Michaelmas, the 29th of September. The plant’s late blooming habit helps to prolong interest in the garden while other flowers fade. Providing a plentiful source of nectar, their late blooms are also popular with bees and butterflies.

A versatile plant that can suit flower beds, wildflower gardens, rock gardens or containers. They range in height from tall elegant 8 ft specimens to dainty 8 inch blooms. Whatever size your garden is you will find an aster flower to fit.

Here is your complete guide to the aster flower.

1 The distinctive aster flower
The distinctive blooms of the Michaelmas daisy can bring color to fading fall gardens.

Aster Flower Varieties

The Michaelmas daisy may not be a new addition to the garden but the range of varieties on offer means there is always something new to discover. There are over 600 known varieties.

The two most commonly grown by amateur gardeners are New England (Symphyotrichum novae-angliae) and New York (S. novi-belgii). However, there are also a range of hybrids available.

2 Aster Flower varieties
Take the time to explore all the plants on offer before selecting the most suitable for your growing conditions. 

Native varieties are often easier to grow than imported plants. These are more likely to be suited to your growing conditions.

Most varieties of the aster flower are hardy in USDA Zones 3 to 8. Some varieties are hardy in zones up to 10. Depending on the variety the plant can reach 1 to 6 ft in height and 1 to 4 ft in spread.

Native North American varieties:

  • New England produces large blooms in shades ranging from deep purple to light magenta.
  • New York asters produce smaller blooms in shades of pink and purple. As well as single blooms, you can also find double flowering varieties.
  • The Smooth aster (S. laeve) is also native to North America. It is a tall cultivar which produces small, lavender blooms.
  • Heath aster (S. ericoides) is a low growing cultivar which produces delicate small, white blooms. A reliable ground cover option Heath aster reaches 3 to 4 ft in height.
  • Calico aster is smaller than the Heath variety but otherwise similar in appearance.
  • Aromatic aster reaches 2 to 4 ft in height and produces blooms about an inch in size. One of the latest blooms to emerge, when brushed they release a pleasing aroma. October Skies is one of the most popular aromatic cultivars.
  • Wood aster ranges in height from 4 to 6 ft. Also known as heart-leaf, the small, delicate blooms about an inch wide dot the plant’s dark stems.
  • Blue wood aster (S. cordifolium) is a bushy plant which produces small, blue-white blooms.

Other less common types include, big leaf, California, Chinese, Italian and Frikart’s aster.

3 Unusual aster flower varieties
In addition to the typical Michaelmas daisy, there are also more unusual varieties such as the Chinese aster available. 

The aster flower can be found at most garden stores. Fully grown Michaelmas daisies, purchased in pots can be planted as soon as they are available. This is usually in the fall. The plants should be hardy enough to survive the winter. You can also purchase seed packets.

Growing from Seed

While you can grow from seed, this is not a reliable process.

Start seeds indoors during the winter. Sow the seeds into pots and place them in a refrigerator for 4 to 6 weeks. This stimulates winter dormancy and encourages germination.

Following their exposure to cold temperatures, sow your chosen seeds in pots or trays filled with fresh potting soil.

Place the pots in a sunny position and allow them to germinate. Keep the soil moist.

Following germination allow the seedlings to grow on in a sunny position. Continue to moisten the soil regularly.

After hardening off the seedlings, from mid-spring onwards, once the last frost has passed you can transplant into pots or beds.

How to Plant an Aster Flower

You can plant from spring until fall. Plant as early as possible to give the aster flower time to establish itself in its new position.

Thsee plants do best in cool areas and moist summers. In warmer areas plant in partial shade to protect the plant from the heat of the midday sun. The soil should be well draining. A loamy soil is ideal.

Poorer soils may need some pre-plating preparation. To do this, use a shovel to work in compost or organic matter. This enriches the soil and improves drainage. As you dig, remove any weeds and large stones that you find.

Dig a hole large enough to hold the plant’s root system. When placed in the hole the top of the root system should sit just below the level of the soil. Sprinkle a source of phosphorus such as organic rock phosphate or superphosphate to help encourage root growth. One teaspoon per plant is plenty.

Position the plant in the center of the hole and backfill. Gently firm down the soil. Water well.

If you are planting more than one aster flower space them 1 to 3 ft apart. The larger the variety the more room it will require.

After watering mulch the soil around the plant. This keeps the roots cool and improves moisture retention. It also deters weeds.

Planting in Pots

Asters can also be grown in pots, as part of a container garden.

Planting in pots is largely the same as planting in the ground. Your chosen pot should be clean and have drainage holes in the bottom. Adding a layer of pebbles or crocks further helps to improve drainage. Fill the pot with a lightweight potting mix and plant as described above.
4 Clean pots filled with fresh soil
Fill clean pots with a light soil mix.

Aster Flower Care

Once established the Michaelmas daisy is pleasingly long lasting and low maintenance. Taller varieties may require staking to help them stay upright. Grow!t Bamboo Stakes provide a sturdy support that blends nicely into your garden.

When to Water

Once established plants in the ground may only require watering if you receive less than 1 inch of rainwater in a week. Remember that plants in pots require more regular watering. Additionally, some varieties, such as New York, require more frequent watering than other cultivars.

Water regularly during the summer months, ensuring that the soil doesn’t dry out. Once flowering has finished you can reduce or even cease watering completely.

Be careful when watering, many aster flower varieties are moisture sensitive. Too much or too little water can cause leaf drop or impair flowering.

Try to keep the foliage as dry as possible during watering. This helps to prevent fungal disease such as powdery mildew.

5 The aster flower is low maintenance
While some varieties may require more regular watering than others this is, in general, a low maintenance plant.

How to Fertilize an Aster Flower

Fertilize with a balanced fertilize in the spring to encourage new growth. A thin layer of compost can also be applied.

These are not heavy feeding plants. Half a cup of organic fertilizer early in the season is usually enough. An evenly balanced fertilizer such as the Miracle-Gro Performance All Purpose fertilizer provides the ideal blend and is easy to apply.

A shovelful of compost can also be placed around the plants in spring. This encourages them to thrive.

An organic mulch around the plants can help to keep the soil moist and as it breaks down enriches the soil and your plants.

Pruning Your Plants

Pinch plants back in early summer. This encourages more blooms and bushier growth.

In the winter cut the plant back once the foliage has died. Some gardeners like to allow the foliage to remain in place for winter interest.

Some varieties may re-seed if spent flowers are not deadheaded. Hybrid seeds won’t produce plants true to the original.

6 Pruning encourages bushier growth
Pruning your plants encourages bushier growth and more flowers to form.

When pruning use a sharp garden scissors. This enables you to make clean, precise cuts. Sterilize your tools before and after use to prevent disease spreading through the garden.

Divide the plants every 2 to 3 years to encourage new blooms and growth. This is best done in the spring.

Common Problems and How to Solve Them

Lace bugs are tiny sap sucking insects that harvest the juice from the plants foliage. If left untouched, they will eventually kill the plant. Regularly inspect your plant for signs of infestation, paying close attention to the undersides of the leaves. The earlier you notice these pests the easier the problem is to treat. Insecticidal soap or a horticultural oil can be used to remove infestations. Simply wipe it on the affected foliage.

Powdery mildew can be a problem in some areas. Keeping the area around the plants tidy, thinning the stems and correctly spacing the plants, so that air can circulate between them, can all help to prevent mildew from forming. A potassium bicarbonate spray can also be used to treat the issue.

Other diseases, while unsightly, rarely harm the plants. To improve their appearance, cut away affected foliage. Remember to sterilize your tools after use.

Rust can also be an issue. However, increasingly cultivars are both mildew and rust resistant.

Wilt can affect plants in poorly draining soil. It is difficult to save wilt affected plants. Instead take cuttings from the healthy part of the plant and root. Lift the rest of the plant and dispose of it correctly. Do not place it on your compost heap.

How to Propagate an Aster Flower

As well as growing from seed, the Michaelmas daisy is easily propagated either by root cuttings or division.

Collecting Seeds

As well as purchasing seeds they are also easy to collect. As the blooms fade, fluffy seed heads, that resemble dandelions, emerge. Each seed is attached to a tuft of fluffy down. This makes them easier to handle than other seeds.

Cut the seed heads from the plant once the down has dried out and turned white. Allow them to dry on a piece of paper for a few days. The down can be left in place if you are sowing immediately. If you are storing the seeds, remove the down to make storage easier.

Seeds lose their viability over time. Storing in an air-tight container in a cool dark place can prolong the lifespan. However, they are best used within a year.

Root Cuttings

To propagate by root cuttings use a clean garden scissors to cut a 2 to 3 inch section of stem from new growth. This is best done in either late spring or early summer. Cut away the lower leaves, allowing only some of the leaves near the top of the cutting to remain in place.

Plant the cutting in a pot filled with a mixture of perlite and sand or vermiculite. Place in a propagator, such as the Tabor Tools Propagator Tray or a plastic bag. Keep the cuttings  in a light position, away from the direct sun. The soil should be kept moist.

After roots have formed remove the cuttings and pot on.

Propagation by Division

Plants can also be propagated by division. Lift the plant and inspect the root for signs of disease. Use a sharp knife to make clean cuts, separating the root system into even sections. Each section should have a healthy amount of roots and several shoots.

Division is best done in the spring just as new shoots emerge. This gives the plants plenty of time to recover and re-establish themselves before winter comes. Division also helps to keep plants healthy. You will need to divide plants every 2 to 4 years depending on the variety.

This form of propagation is best done on alpine types of aster that have a compact or mounding growth habit.

7 Aster flowers provide nectar
Bright and attractive, the Michaelmas daisy is an important late season source of nectar for many pollinators. 

The star shaped blooms of the Michaelmas daisy add color and interest to fall gardens that may otherwise begin to look a little dull. Looking particularly effective when planted alongside other late summer eye catching plants such as goldenrod and coneflower, the aster is a striking addition to any garden.

A popular later season source of nectar, an aster flower will attract scores of bees and butterflies to your garden. Easy to care for and attractive, why not add the aster flower to your garden today?

Aster Flower 1 Aster Fower 2