How to grow asters
All you need to know about growing asters, or Michaelmas daisies, in this detailed Grow Guide.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sow | yes | yes | ||||||||||
| Plant | yes | yes | yes | |||||||||
| Flowers | yes | yes | yes | yes |
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Asters are in the daisy family, and most of the varieties grown in the UK are perennial, meaning they come back every year. They generally flower in late summer and autumn, which gives them their common name Michaelmas daisy. Asters are ideal for growing in mixed borders, with grasses and other prairie-type perennials. In botanical terms there are two main types of aster – North American and European. Most North American species come under the name of Symphyotrichum or Eurybia, but many people still refer to them as asters.
Asters are a great transition plant, bridging the seasons from summer to autumn. Their bright, daisy-like aster flowers make a colourful splash and provide a rich source of nectar and pollen for late-flying insects. Many varieties also make good cut flowers.
Where to grow asters
Grow asters in dappled or partial shade, in any type of soil, although slightly moist soil (that never dries out) is preferable for species prone to developing powdery mildew. Asters can also be grown successfully in containers, again, preferably where the soil remains slightly moist, or choose European asters, which have greater resistance to powdery mildew.
When to plant asters
Asters in containers are best planted from March to early May. They can be planted in the summer, but will need far more watering than those planted earlier in the year. Asters are also available to buy in the winter as bare-root plants. These tend to be cheaper and they should be planted as soon as possible, provided the ground isn’t frozen or waterlogged.
How to plant asters
Asters are easy to plant. Plant them as you would any perennial, ensuring they have plenty of space to grow and keeping them well watered as they establish. Some asters work well as ground cover, while other varieties can grow up to 2m tall. Most asters don’t need staking, but some of the tall varieties may need staking in windy areas.
Watch our video guide with Monty Don on how to plant asters:
How to care for asters
Deadhead aster flowers to keep them looking good and to encourage more blooms to form. Cut aster plants back hard after flowering in late autumn. In midsummer, pinch out the top shoots to encourage flowers.
Asters in pots will need regular watering, but plants in the ground should only need watering in prolonged dry periods. They respond best to a good watering when the soil is dry, rather than frequent light watering. Asters do not grow well in damp and waterlogged soils. Asters don’t generally need feeding, but adding an organic mulch in spring is beneficial.
Overwintering asters is straightforward provided the ground doesn’t become waterlogged in winter. Many of the asters grown in the UK are hardy down to -20°C, but the combination of wet soil conditions and cold winter temperature can kill them. Asters in containers should be brought into a frost-free place overwinter.
How to propagate asters
Increase your stock of asters by taking softwood cuttings between April and August (bear in mind that the process from taking cuttings to having flowering plants can take over two years).
Remove non-flowering shoots, cutting them down to a few centimetres in length, and then remove the lower leaves. Push each cutting into a pot of moist but gritty compost. Cover with a clear polythene bag or pop the pot in a propagator. Check the compost regularly and ensure it doesn't dry out, so the cuttings have the best chance of taking root. Pot the cuttings into individual containers at the first signs of growth (after about six to eight weeks). Plant the young plants out in spring and they will flower the following year.
Asters can also be propagated by division. Usually after around three years, the clumps are large enough to divide. Simply dig up and halve or quarter the clump with a sharp spade. Replant the clumps immediately into their new positions and water well.
Pests and diseases
Mildew is a common problem among many aster varieties, particularly the North American varieties. Keep plants well-watered and don’t let the soil dry out, but also look for varieties that are more mildew-resistant. European asters, including Aster amellus, Aster pyrenaeus and Aster x frikartii are all mildew resistant, as are Eurybia x herveyi, the Japanese aster, Kalimeris incisa, and Symphyotrichum ‘Little Carlow’.
Advice on buying asters
- Choose your aster flowers carefully – if you have drier soils then opt for European or certified mildew-resistant varieties
- Always check plants for signs of damage or disease before buying or planting
- Asters are available to buy from garden centres and nurseries but you'll find a wider selection from specialist nurseries and online
Where to buy asters
Great aster varieties to grow
Symphyotrichum ‘Ochtendgloren’ (pilosum var pringlei hybrid) – previously known as Aster ‘Ochtendgloren’, this has typical lavender flowers with bright yellow centres. A taller variety, it works well at the back of a border
Symphyotrichum laeve ‘Calliope’ – a particularly tall aster, with masses of small, lilac-blue flowers with yellow centres
Symphyotrichum novi-belgii 'Samoa' (‘Dasthree’) (‘Island Series’) – with purple flowers with bright yellow centres
Symphyotrichum ‘Coombe Fishacre’ – the small, lilac-blue flowers have yellow to purple-brown centres
Frequently asked questions
Are asters poisonous to pets?
Asters aren’t known to be poisonous to pets, however the charity Cats Protection does list asters in the category ‘Caution Advised’ as ingesting them has been known to cause gastrointestinal upset in cats. Eating any plant material can potentially cause stomach upsets in cats and dogs.
Do asters spread?
Asters can spread by seed and by stolons (horizontal stems that grow along the surface of the soil). Remove seedlings and lift clumps every three or four years, divide plants and replant or give away unwanted portions. Take care not to let asters spread beyond your garden as some varieties can be invasive in the wild.
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