Aster
Symphyotrichum
Autumn daisy that keeps pollinators fed when little else flowers.
- Type
- Flower · Perennial
- Botanical family
- Mixed / other
- Foliage color
- Green
- Flower color
- Purple and violet
- Sunlight
- Full sun to part shade
- Watering
- Moderate
- Soil
- Fertile, moist, well-drained
- Feeding
- A balanced feed in spring, with compost laid over as a mulch.
- USDA zones
- 3a–8b
- Frost tolerant
- Yes
- Flowering
- September
- Pruning
- Cut the stems back by a third in May to keep the plant compact, then take it to the ground in autumn.
- Sow indoors
- 42 days before the last spring frost
- Plant out
- at the last spring frost
- First harvest
- 100 days after the last spring frost
- Harvest ends
- at the first fall frost
- Apr–Sep Spring Growth
- Sep–Oct Flowering
- Oct–Nov Growing
- Nov–Dec Leaf Fall
- Jan–Apr Leaf Fall
- Plant spacing
- 15.7 in
- In-row spacing
- 13.8 in
- Between rows
- 17.7 in
- Square-foot density
- 1 per square
- Root system
- Running rhizomes
- Working depth
- 4–12 in
- Can reach
- 18 in down where the soil allows
- Spread
- 3.5–6.5 ft across, about 2–4× the width of the plant
- Shallowest pot
- 12 in of soil
It travels underground, and it does not stop where you would like it to. Taking the tops off does nothing at all to the run, and every fragment left behind is a new plant. In open ground the only boundary that holds is a barrier sunk two spits deep, or a container with its rim standing clear of the soil.
The habit is Aster’s own; the figures are what that habit usually comes to at this size, not a measurement of this species. Roots follow the soil either way: a compacted pan, a high water table or heavy clay stops them well short of any of it, and deep open ground lets them go further.
- When
- Cut in cool morning; annual China asters peak late summer, perennial asters late summer into autumn — a valuable late-season cut.
- What to look for
- Cut when the flower is three-quarters to fully open with a still-tight center; aster buds cut too green refuse to open in water.
- How to harvest
- Cut long stems with sharp snips just above a node or side shoot, strip the lower half of foliage (aster leaves blacken in water), and stand in cool water for a few hours before arranging.
- How often
- Cutting sprays and deadheading weekly prolongs the display several weeks; on perennial asters, cutting mainstems brings on side sprays.
- Storing the crop
- Excellent vase life, 7–14 days, among the best of the daisies; change water every 2–3 days. Seed-save from fluffy browned heads — sow fresh or store cool and dry (China aster seed is short-lived, use within 1–2 years).
Beneficial predators that hunt this plant's pests — grow their favourite flowers nearby to recruit them. companion plant
- Aphid midge Aphidoletes aphidimyzaHunts Aphids
A tiny midge whose orange maggots paralyze aphids and drink them dry, twenty or more each. Sold as a greenhouse biological control and resident outdoors wherever there are small nectar flowers and an unsprayed aphid colony to find.
- Assassin bug ReduviidaeHunts Aphids
A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be.
- Big-eyed bug Geocoris spp.Hunts Aphids
A stubby 3 mm bug with enormous wrap-around eyes, working the soil surface and the low foliage for aphids, mites, thrips and insect eggs. It is the main natural check on chinch bugs in a lawn and it is killed outright by insecticide.
- Damsel bug NabidaeHunts Aphids
A slender, mantis-armed bug that grabs aphids, small caterpillars, and thrips in low crops and meadowy edges. Leave a strip of unmown grasses and flowers for it to overwinter in.
- Dragonflies & damselflies OdonataHunts Aphids
Aerial hunters that take mosquitoes, midges and small flies on the wing all day, and whose larvae spend a year or more clearing the same insects from the water. A pond with planted margins and no fish is the way to have them.
- Garden birds PasseriformesHunts Aphids
Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray.
- Green lacewing Chrysoperla carneaHunts Aphids
Its bristly larvae — "aphid lions" — impale aphids, mealybugs, thrips, and mite colonies, eating hundreds a week. Adults feed on nectar and pollen from small open flowers and overwinter in hollow stems left standing.
- Hoverfly SyrphidaeHunts Aphids
Bee-mimicking flies whose legless larvae graze aphid colonies clean while the adults pollinate. A ribbon of shallow, nectar-rich flowers kept in bloom all season recruits wave after wave of them.
- Ladybird (lady beetle) CoccinellidaeHunts Aphids
The gardener’s favorite ally: adults and their alligator-shaped larvae each eat thousands of aphids, plus scale, mealybugs, and other soft-bodied sap-suckers. Grow flat, open flowers for the adults and never spray a colony that ladybird larvae are already working.
- Minute pirate bug Orius spp.Hunts Aphids
A pinhead-sized true bug that is the best natural check on thrips, and happily spears aphids, mites, and insect eggs too. It needs pollen when prey is scarce, so keep something flowering nearby.
- Parasitic wasps Braconidae & TrichogrammaHunts Aphids
Tiny, stingless wasps that lay eggs in or on caterpillars, aphids, and moth eggs — the white cocoons riding a hornworm are their calling card, so leave that caterpillar be. Umbel flowers with shallow nectar keep the adults fuelled.
- Praying mantis MantidaeHunts Aphids
A sit-and-wait ambusher that snatches caterpillars, beetles, and anything else that wanders close — friend and foe alike, so count it a mixed blessing. Tall, structured plantings give it perches and egg-case anchors.
- Soldier beetle CantharidaeHunts Aphids
Soft-winged beetles seen mating on flower heads in high summer; adults and larvae both take aphids and soft grubs. Open composite flowers are their landing pads and hunting grounds.
- Spiders AraneaeHunts Aphids
Webs, ambushes, and night patrols make spiders the garden’s steadiest generalist predators, taking whatever flies or crawls past. Mulch, ground cover, and undisturbed corners keep the population dense.
Grasses, Sedum, Rudbeckia, Anemone
Good neighbors
'Aster' is Greek for star — and they flower late, feeding bees well into autumn.
The Cottage Garden Companion — the gardener's herbarium at cottagegardencompanion.com