how to plant, grow & care for asters
complete growing guide
Perennial asters score high in the autumn garden, not least because of the range of colours they come in – there are fabulous carmine pinks and deep rich purples, as well as pastel shades and white. I lean toward the more intense, deep pinks and mauves, which turn the central yellow heart of every flower into gold – a fantastic combination. They are an invaluable plant for those of us who want to keep our garden full of colour late in the year.
Asters have been through a bit of scientific renaming of late, with the New England asters now known as Symphyotrichum novae-angliae and the asters commonly known as Michaelmas daisies, now Symphyotrichum novi-belgii.
Whatever the name, they are loved as a simple cottage garden stalwart that flower long and hard in almost any soil and are laden with pollen and nectar for insects. They also have an exceptionally long vase life, particularly the Aster amellus varieties – pick them and put them in a vase and, if kept cool, they can last more than a fortnight.
No garden is complete without its asters and we have chosen only the very best to include in our range of young plants. Browse our aster varieties, which all grow quickly and easily.
- Common name Michaelmas daisy
- Latin name Aster
- Type Perennial
- Height 40cm (16in) to 1.2m (4ft)
- Spread 45cm (1½ft)
- TLC rating Easy
- Aspect Full Sun
- Planting position Middle of border
- Suitable for pots Yes
- Good for pollinators Yes
- Good for cut flowers Yes
how to grow asters
where to grow asters
Soil type: Soil should be moist, well-drained and average- to humus-rich.
Aspect & position: Full sun to part sun is ideal for asters, and a sheltered position is preferred.
when to plant asters
Young aster plants can be planted directly into borders in spring for flowers in autumn, or alternatively plant out in early autumn to establish before winter and for flowers the following year.
how to plant asters
Plant young asters in groups of three or more for a good display. Plant directly into borders during spring for late-summer and autumn flowers.
Dig a hole that’s just a little deeper than the pot the plant came out of. Add grit to the base of the hole on heavy ground to improve drainage – asters don’t like to sit wet through winter.
Allow good spacing between the plants to aid air circulation and help prevent problems with mildew.
Water well after planting and water regularly until established.
Pinch out a third of the flowering stems in midsummer to encourage a longer flowering season. It’s possible to cut down hard after the asters have finished flowering in October, or leave the seed heads in place for winter interest and to support wildlife.
growing asters in a pot
Asters can be grown in containers in well-drained compost. Plant in multipurpose compost in planting holes a little deeper than the pot the young plant came out of.
After flowering, the plants should be cut back and then overwintered – store them in a cold frame or greenhouse over the coldest months.
When there is the first sign of new growth in spring, remove the plants from their containers and repot in fresh compost. This is the time to divide them if they are large enough. Once repotted, slowly harden them off and do not let the compost dry out.
how to care for asters
Asters don’t like to sit in soggy soil – wet, humid conditions will only increase the chance of powdery mildew. Water well on planting and regularly while establishing, but then only water when dry. Keep an eye on asters growing in pots as these will dry out more quickly.
Feeding isn’t essential for asters, but a slow release fertiliser added a couple of times a year will give the plants a boost.
Deadhead faded flowers through the growing season. You can cut down hard after the asters have finished flowering in October or November, but I like to leave them standing over winter for wildlife as the seed heads are loved by birds.
Most asters will need dividing every fourth year to maintain vigour. All asters are best divided in spring as new growth starts. Lift the clump and then use two back-to-back forks to split it. Take care of old stems, they can be sharp. Some varieties are denser and may need a knife or spade to cut through. Discard old woody pieces and use newer sections from the outside of the clump to replant. Add grit to the base of the hole on heavy ground before planting and water until established.
Asters are fine left in the ground during winter if the soil is well-drained. Any asters growing in pots should be cut back after flowering and then stored in a cold frame or greenhouse.
- Plant out young aster plants in borders and pots.
- Pinch out a third of the flowering stems in midsummer to encourage a longer flowering season.
- Cut back asters in pots once flowering is over.
- Store asters in pots undercover over winter.
pests, diseases & common issues
Asters have a tendency to suffer from powdery mildew, which is a fungal disease that shows up as a powdery coating on the foliage. For prevention, plant your plants widely to allow for air circulation. You can also remove any affected leaves and try an organic solution such as homemade comfrey tonic to keep mildew at bay.
why is there rust on the leaves of my aster?
This could indicate a type of leaf spot, a range of fungal diseases whose symptoms include brown or rusty spots on the leaves. Make sure the plant isn’t under stress through over or under watering, remove any affected leaves and clear any fallen leaves from the ground to avoid spreading the disease.
do my asters have botrytis blight?
The fungus botrytis, commonly known as grey mould, can affect asters. It normally shows up on plants under stress. Symptoms include shrivelled leaves and fluffy grey mould – damp conditions and poor air circulation are often the cause. Tidy up any dead leaves or debris around the plant and avoid overhead watering as this tends to spread the fungal spores.
why are my asters turning brown?
Asters can suffer with what’s known as fusarium wilt, which is a fungal disease. Fusarium wilt causes discoloration of the stems and foliage, as well as stunted growth. Root and stem decay shows up as blackened stem bases. If you suspect this is the case, lift and destroy the plant to prevent its spread.
frequently asked questions
are asters annuals or perennials?
Asters are perennial and if they’re planted in a sunny spot in free-draining soil they will return year after year.
what do aster flowers look like?
Asters look very much like daisies and come in a range of colours, from deep pink and purple, to pale shades.
are aster flowers edible?
Yes, asters are technically edible, though the flowers have a bitter flavour. The root is traditionally used in Chinese medicine.
how do you cut asters?
Always harvest cut flowers for the vase early in the morning and plunge them straight into cold water. Cut along the stem above a bud so the plant can develop more flowers.
how deep should you plant asters?
Dig a hole that is a little deeper than the pot the young plant is growing in.
is the aster plant a mosquito magnet?
We’ve not heard this before! We do know they attract a lot of great insects and pollinators, including hoverflies.
do rabbits eat aster plants?
Yes, hungry rabbits are known to munch asters.
are asters frost hardy?
Asters are frost hardy and will be fine in the borders over winter, emerging again in spring. Asters growing in pots should be brought undercover over winter.
do you deadhead asters?
There’s no need to deadhead asters, but removing faded flowers will keep the plant looking fresh.
do asters spread?
Asters do spread year on year and will need to be lifted and divided every fourth year to avoid congestion.
how often should you water asters?
Asters don’t like sitting in soggy soil or being wet through winter, so well-drained soil is essential. Water well on planting and then water regularly while they establish. Water in a drought and keep an eye on asters growing in pots as these will dry out faster.
how to cut & arrange asters
Asters are well known for their exceptionally long vase life. Pick them and put them in a vase and – kept cool – they can last more than a fortnight. If you strip all the leaves below the water line and thin out the leaves up the stem a bit more, and put a drop of vinegar in the water, it will maximise the cut-flower potential.
Mix the rich purple and magenta colours with late-flowering crocosmias, a few searing pink nerines, a hydrangea or two and the bright, sparky foliage of the almost perpetual-flowering Euphorbia ceratocarpa and Cyperus eragrostis and they look exceptional.
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