Symphyotrichum oblongifolium: grow fall asters

Published on 15 September 2026

Aromatic aster is the one to grow when every other perennial has given up. Low, dome-shaped and wiry, it smothers itself in lavender-blue daisies with amber-gold centres from late September well into November, long after the New England asters have gone over. Brush past it and the narrow grey-green leaves release a distinctly balsamic, minty scent — the trait that gives the plant its common name.

Growing conditions

Give aromatic aster the sunniest, most open position you have — a minimum of six hours of direct sun, and ideally more. In light shade the stems stretch, flowering thins out and the neat dome collapses into a sprawl. Good air movement around the plant also helps keep the foliage clean.

Drainage matters far more than fertility. Sandy, stony, chalky and ordinary free-draining loams all suit it, and it performs willingly on alkaline ground where many perennials sulk. A pH of roughly 6.0 to 8.0 is fine; heavy, wet clay in winter is the one situation it genuinely resents, so raise the bed or work in grit if that is your soil.

It is exceptionally hardy and exceptionally drought-tolerant once settled, making it a strong choice for gravel gardens, hot borders and dry banks across temperate Europe and North America. In wetter maritime climates, lean soil and full exposure are the key to keeping it compact.

How to plant Symphyotrichum

Spring planting is best, from March to May, giving the roots a full season to establish before their first winter. Autumn planting also works in mild, well-drained gardens, but avoid setting out young plants into cold, saturated soil.

Spacing: 45–60 cm apart — the plants build broad mounds and crowding encourages soft, mildew-prone growth.
Depth: Set the crown level with the surrounding soil; burying it invites rot at the base.
Soil preparation: Fork the base of the hole to break any pan and add grit or coarse sand to heavy ground. Skip the rich manure — lush plants flop.
Watering in: Soak thoroughly after planting, then water weekly for the first six to eight weeks only; after that, leave it largely to its own devices.
Propagation: Divide established clumps in early spring, discarding the woody centre, or take 8 cm basal cuttings in late spring — they root in two to three weeks in a gritty mix.

Symphyotrichum oblongifolium growing in a garden border — Symphyotrichum oblongifolium growing in a naturalistic garden border

Care through the seasons

Spring: Cut away any remaining old stems as the new shoots appear at the base. A light mulch of leaf mould or garden compost is plenty; avoid high-nitrogen feeds, which produce weak growth. Divide congested clumps every three to four years when the centre begins to thin.

Summer: Trim the whole plant back by a third to a half in late May or early June — the classic “Chelsea chop” — to create a dense, self-supporting cushion and delay flowering slightly. Watering is rarely needed except during prolonged drought in the first year. Remove any stems that flop into neighbours.

Autumn: This is the plant’s moment, so simply enjoy the display and let the pollinators work. Deadheading is unnecessary and the seedheads feed finches through early winter. Leave cutting back until late winter rather than tidying immediately after flowering.

Winter: The top growth dies back to a woody crown and needs no protection in any temperate garden. Standing stems offer overwintering shelter for insects, so delay clearing them until late February.

Best varieties to grow

A handful of named selections offer better habit and flower colour than seed-raised plants.

‘October Skies’ — compact at 45–60 cm, with violet-blue flowers on a tidy, reliably self-supporting dome; the best choice for smaller borders.
‘Raydon’s Favorite’ — taller and looser at 75–90 cm, with lavender-blue daisies and strongly aromatic foliage; superb for prairie-style planting.
‘Dream of Beauty’ — a low, spreading pink-flowered form around 30–40 cm, excellent as a late-season edging or ground cover.
‘Fanny’s Aster’ — very late flowering, often into November, with deep blue-purple blooms on a mounded 60 cm plant.

Pests, diseases and common problems

Powdery mildew: Grey-white bloom on the leaves, worst in dry soil with stagnant air. This species is naturally resistant, so the usual cause is overcrowding — thin the clump, widen spacing and water the roots rather than the foliage.
Floppy, splayed stems: Caused by shade, rich soil or over-feeding. Cut back by a third in late May, reduce feeding entirely and move plants into full sun.
Slugs and snails on new shoots: Emerging spring growth can be grazed to the ground. Apply a gritty barrier around the crown or use ferric-phosphate pellets, and avoid mulching too thickly right against the stems.

Frequently asked questions

Key tip: Treat aromatic aster meanly — full sun, lean well-drained soil and no feeding — and it will repay you with a self-supporting dome of flower when the rest of the border is finished.

When should I plant Symphyotrichum oblongifolium?

Plant in spring, between March and May, so the roots establish through the growing season. Container-grown plants can also go in during September in free-draining soil, but avoid autumn planting on heavy clay where winter wet causes crown rot.

Does aromatic aster spread, and is it invasive?

It spreads slowly by short rhizomes, widening into a clump of 60–90 cm over several years rather than running through a border. It can self-seed modestly in open gravel; deadheading in late autumn prevents this if you would rather it stayed put. It is not considered invasive and is far better behaved than many taller asters.

Why is my aromatic aster flopping and bare at the base?

Almost always too much shade, too much water or soil that is too rich. Move it to full sun, stop feeding, and cut all stems back by a third to a half in late May or early June — the resulting plant will be shorter, bushier and need no staking.

Is aromatic aster a good choice for a dry garden or pollinator planting?

It is one of the best. Its limestone-glade origins make it more drought- and alkaline-tolerant than Symphyotrichum novae-angliae or S. novi-belgii, and it flowers weeks later, providing nectar for late bumblebees, hoverflies and migrating butterflies into November. Pair it with Sedum, Perovskia and autumn-flowering grasses for a display that needs almost no irrigation.