Asters

Asters are a beautiful–and easy-to-care-for–addition to any garden. Typically blooming in late summer and fall, the plants produce striking composite flowers. The fragrant and colourful blooms attract butterflies, bees, and birds. With over 600 species to choose from, it’s easy to find a variety that suits your garden’s setting and microclimate.

Flowering Characteristics

A flowering aster is a beautiful plant. It produces small (1-5 cm) daisy-like blooms that are composite flowers. As the Canadian Wildlife Federation explains, “this means that each flower is actually a group of smaller flowers consisting of ray flowers (petals) surrounding disk flowers (the centre). Disk flowers are usually yellow or burgundy, which makes a nice contrast with the blue, purple, violet, or white ray flowers.”

The colourful, fragrant blooms attract birds and insects, including butterflies. Most aster varieties bloom in late summer to early fall. As the Ontario Parks website points out, that timing means that asters are an important source of nectar for monarch butterflies as they ready themselves for their migration to Mexico.

But asters are an important food source for other butterflies too and the larvae of many different butterflies and moths.

Habitat

Asters are native to North America (including Canada) and southern Europe. Most species are perennials, but there are a few that are annuals or biennials. They grow in the wild across Canada, propagating by seeds dispersed on the wind. The plants appear in many different habitats, including wetlands, forested areas, and mountain regions. Different varieties are hardy from Zones 3-8. It is no surprise then that asters are easy to grow.

Some species can thrive in just about any garden. According to the Canadian Wildlife Federation, for example, Lindley’s aster (Aster ciliolatus) grows in full sun to partial shade, in dry to moist soils. Other varieties are more particular. The New York aster (A. novi-belgii), for instance, requires full sun and moist soil to flourish.

Care

As long as you choose a species suited to your garden’s microclimate, asters are one of the easiest perennials to grow. The one issue to watch for is powdery mildew. Be proactive in protecting your plants from this fungal disease by keeping moisture above ground to a minimum. Leave lots of space between plants for air circulation. As well, water at soil level (rather than using an oscillating sprinkler) in the morning so that wet leaves can dry quickly. And, amending the soil with compost is always an excellent way to enhance the health of any garden plants.

Species

The Canadian Wildlife Federation website is an excellent resource for choosing the right asters for your garden’s microclimate. While all asters attract butterflies and moths, cross-check the Carolinian Canada website if you’re planting to attract certain insect species.

Lindley’s Aster or Fringed Blue Aster (Symphyotrichum ciliolatum formerly Aster ciliolatus)

This species produces 2.5-3cm flowers. The sparse ray petals are thin and long, and are pale to deep blue or violet in colour. The disc flowers change colour from yellow (when budding and first open) to purple (when pollinated). The changing colour signals pollinators, letting them know which flowers are rich in nectar. The plants range from 30cm to 1m in height.

Lindley’s Aster is native to British Columbia, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, and Nova Scotia. It prefers full sun but will grow in partially shaded areas as well. This species is not picky about soils, growing in poor soils and ones that range from dry to moist.

Blue Wood Aster or Heart-leaved Aster (Symphyotrichum cordifolium formerly Aster cordifolius)

The small 1.5cm ray flowers on this species may be pale blue, blue-violet, rose, mauve, or occasionally white. Like Lindley’s Aster, the disc flowers of Blue Wood Asters are initially yellow but change to purple. The change in colour lets pollinators know which flowers have nectar available. This variety grows quite tall, ranging from 60cm to 2m in height.

Blue Wood Asters are native to Manitoba, Ontario, Quebec, Newfoundland, New Brunswick, Prince Edward Island, and Nova Scotia. Its natural habitat is in open woods and on the edges of woods. It grows in light shade to full sun and is drought-tolerant.

Heath Aster (Symphyotrichum ericoides, formerly Aster ericoidesoides)

This beautiful aster produces dense clusters of small 1cm white ray flowers that spread along its branches. Its disc flowers change from yellow to brown as a way to direct pollinators to those blooms that have abundant nectar.

Heath Asters grow naturally in the Yukon and Northwest Territories as well as in Alberta, Saskatchewan, Manitoba, Ontario, and Quebec. They prefer open sky and full sun, growing in grasslands, fields, meadows, and ditches. Heath Asters are not picky about soil types or moisture levels.

Heath Asters are one of the host plants for silvery checkerspot and northern pearl crescent butterflies.

New England Aster (Symphyotrichum novae-angliae formerly Aster novae-angliae)

When people visualize asters, this is the variety they most likely think of. New England Asters are often sold in garden nurseries. Its large ray flowers have numerous petals that are usually blue/violet but may also be pink or occasionally white. Its disc flowers change from yellow to purple as a signal to pollinators.

New England Asters are native to Saskatchewan, Manitoba, Ontario, and Quebec. They grow naturally in open spaces, in fields and along the edges of swamps and wooded areas. New England Asters prefer full sun but will tolerate partial shade. They will flourish in dry to moist soils.

Like Heath Asters, New England Asters are a host plant for silvery checkerspot and northern pearl crescent butterflies.

New York Aster (Symphyotrichum novi-belgii formerly Aster novi-belgii)

New York Asters are very similar in appearance to New England Asters. Both varieties produce abundant large ray flowers with numerous petals in shades of blue/violet, pink, and occasionally white. The height of New York Asters is dependent on soil conditions. In drier, sandy soils, the plants tend to be short (around 30cm). In rich, loamy soils, the plants may grow as tall as 180cm.

This variety grows naturally in Quebec, Newfoundland, New Brunswick, Nova Scotia, and Prince Edward Island. It prefers damp soil and full sun, often establishing itself near the coast.

Asters are one of the best native plants for a butterfly garden, as all varieties of the flowers attract butterflies and moths. If you’re hoping to attract a specific species of butterfly, cross-check the Carolinian Canada website to see which variety of aster is most likely to entice those butterflies to your garden. Otherwise, just choose the asters that appeal most to you, based on their size and bloom colour, and wait for the butterflies to arrive.