Michaelmas daisy

Sun

Full sun gives the strongest stems and best flowering; light shade is tolerated but can encourage flopping and mildew.

Water

Keep the soil evenly moist, especially during establishment and summer dry spells. Established plants tolerate brief dry periods, but prolonged drought often spoils the lower foliage.

Soil

Moist, fertile, well-drained soil; tolerates clay if it is not persistently waterlogged. Suitable for mildly acidic to alkaline soils.

Height

3-5 ft (0.9-1.5 m); dwarf garden selections are shorter

Spread

2-3 ft (0.6-0.9 m), expanding farther through underground rhizomes if left unchecked

Flowers

Late summer to mid-autumn; the species usually has violet-blue rays around yellow centres, while garden selections include purple, pink, white and reddish pink.

Foliage

Narrow, green, mostly smooth leaves on branching stems; upper leaves clasp the stems. Top growth dies back for winter.

Growth

Fast; forms a substantial clump within a few growing seasons.

Care needed

Medium

• Pollinators
• Cold hardy
• Wildlife
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Moderate

Toughness

Fairly tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   2.5 ft (0.76 m)

3. After 2 years

   4 ft (1.2 m)

   full size

About 2 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Native to

the US and Canada

In the garden

Spreads vigorously: plan to contain it.

Growth rate

Fast

• Water deeply during dry spells, directing water to the soil rather than over the leaves.
• Apply compost and a moisture-retaining mulch in spring, keeping the crown clear.
• Avoid heavy nitrogen feeding, which encourages weak stems and excessive leafy growth.
• Support tall selections with twiggy stakes or a plant ring before stems become tall.
• Divide congested clumps every two to three years in spring, replanting vigorous outer pieces.
• Remove wandering shoots where the clump is crowding neighbouring plants.

Pruning. For shorter, bushier plants, cut stems back by about one-third in late spring; this can delay flowering slightly. Cut dead stems to near ground level in late winter or early spring, or remove them earlier if badly diseased.

Late winter

Cut down old stems before new shoots emerge; remove badly mildewed plant debris.

Early spring

Plant or divide clumps, water thoroughly and mulch with compost.

Late spring

Install supports and optionally shorten stems to encourage a bushier habit.

Summer

Water during dry spells and check lower leaves for mildew.

Late summer

Enjoy flowering and remove selected faded heads if you want to reduce self-seeding.

Autumn

Mark spreading clumps for spring division; leave healthy stems standing for winter habitat.

• Plant through the middle or back of a sunny mixed border to carry colour beyond summer.
• Combine with ornamental grasses and sedums for contrasting flower shapes and autumn seedheads.
• Use repeated groups in a cottage garden with phlox and rudbeckias for a loose, layered effect.
• Include in a pollinator border with other late-flowering perennials, allowing space for its spreading roots.

Garden styles it suits: Cottage garden, English country, New perennial (prairie), Pollinator garden, Autumn colour and Blues and silvers.

Plant it with: Black-eyed Susan, Garden phlox, Autumn stonecrop, Switchgrass, Feather reed grass and Japanese anemone.

Wildlife: Open flowers attract bees, hoverflies, butterflies and other late-season pollinators. Dense, double-flowered selections usually offer less accessible pollen and nectar. Retained stems provide shelter for overwintering invertebrates.

• Powdery mildew: give plants full sun, maintain soil moisture, divide crowded clumps and choose mildew-resistant selections.
• Aster rust: remove affected leaves and fallen debris, improve airflow and avoid wetting foliage when watering.
• Slugs and snails: protect emerging spring shoots with hand-picking or iron-phosphate bait used according to the label.
• Flopping stems: provide early support, avoid rich nitrogen feeds and shorten shoots in late spring if needed.

Not known to be toxic to people, cats, dogs or horses. No part is recognised as seriously poisonous, although eating garden plants can cause stomach upset and they should not be treated as food.

Where it spreads. Spreads vigorously by rhizomes in moist, fertile soil. It is naturalised and can be invasive in parts of Europe, including Belgium and Germany, especially in damp grassland and along waterways. Escaped plants may be hybrids rather than the pure species; keep garden clumps contained and do not dump divisions in the countryside.

• New England aster (Symphyotrichum novae-angliae)

  Usually has conspicuously hairy stems and rough, hairy leaves; Michaelmas daisy generally has smoother stems and leaves.

• Smooth aster (Symphyotrichum laeve)

  Typically has conspicuously blue-green, waxy leaves and stems, with broad, clasping leaf bases; Michaelmas daisy is usually greener and less waxy.

Michaelmas daisy refers to flowering around the feast of St Michael on 29 September in the Northern Hemisphere, while novi-belgii means 'of New Belgium', an old name associated with the Dutch colonial region around present-day New York.

Propagation. Divide in spring or take basal cuttings from young shoots. Seed can be sown in spring, but seedlings from named selections will not reliably match the parent.

Accepted botanical name

Symphyotrichum novi-belgii

In the US and Canada

Native in Canada, the lower 48 states and St. Pierre and Miquelon.

Native range

Connecticut, Labrador, Maine, Maryland, Masachusettes, New Brunswick, New Hampshire, New Jersey, New York, Newfoundland, North Carolina and Nova Scotia.

Measured

Soil pH 7 to 7.5. Average height 79 cm.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.