Dictionary of Flowers: Aster (Michaelmas Daisy)

Only Nature could invent beauty like the Aster. Image used under a Creative Commons licence with the kind permission of Manu and Flickr

Aster
Common name: aster, Michaelmas daisy
Family: Asteraceae
Category: Perennial in USDA zones 3-9 depending on species
Height: 24" and up, depending on species
Width: 12" and up, depending on species
Sun/part shade
Blooms: late summer to mid-fall
Attracts: butterflies
Growth habit: mounding, vertical. Used as a filler in container combinations
Maintenance: average
Soil: average to rich, well drained, dry to moist. Water regularly if grown in containers.
Garden uses: containers, mixed border, rock garden, wildflower garden
Diseases: root rot, leaf spot, wilt
Pests: aphids, whitefly, thrips

Aster is a large genus of flowering perennials, with daisy-like blooms in many colors ranging from purple to pink and red and white.

Aster means "star" in ancient Greek, a reference to the flower's shape. They offer late color in the garden during late summer and fall, when other perennials stop blooming.

Although asters' height ranges from one to eight feet, the ones best suited for containers are the shorter varieties, up to three feet. Most asters grow from creeping rhizomes. Taller varieties require stalking.

The aster genus can be divided into three large groups: asters that grow in woodland areas (they prefer part shade and humus rich soils).

Asters that grow on meadows, prairies or roadsides (these asters prefer average soil to rich moist soil and sun) and the third group are asters that grow on mountainsides or seaside (require full sun, excellent drainage and average to rich soil).

They all benefit from division every two to three years and pinching back in spring to keep them bushy and encourage flower production.

Remove spent flowers to keep asters blooming longer.

Clusters of Michaelmas Daisies look great in pots and containers. Image used under a Creative Commons licence with the kind permission of Tanaka Juuyoh and Flickr

They require average watering and supplemental water in dry zones during summer. It's a good idea to mulch around the plant to preserve moisture.

Do not allow the soil to dry, since it stresses the plants.

They benefit from the yearly application of compost around the plants in the spring and a once a month feeding with a balanced fertilizer during the summer months.

Asters can be propagated by division, seed or softwood cuttings. The cuttings should have two or three leaf nodes. Remove leaves from the bottom of the cutting, dip the end in rooting hormone, pot up in moist potting mix and cover with plastic. Keep in the shade, watering as needed until roots develop.

To grow asters from seed, cold stratify the seed for four weeks, then plant it in moist starting mix, barely covering it.

If kept between 65-75° F, they should germinate in two weeks to a month. They can be wintersown.

Insects also love Aster flowers. Image used under a Creative Commons licence with the kind permission of Christine Majul and Flickr

Asters are somewhat prone to disease. Fungal diseases such as leaf spot, stem rot or root rot need to be treated with an antifungal. Root rot can be prevented by good drainage. They are also prone to viral diseases.

In this case, the plant needs to be discarded, as they cannot be treated. Aphids, whitefly or thrips can attack asters. Use a pesticide if you notice any of these pests' damage to the plant.

Asters are deer resistant. They are an important source of nectar for butterflies in late summer gardens.

Popular varieties:

Aster alpinus - short variety, purple. Blooms in summer
Aster divaricatus - short with small white flowers during September and October
Aster dumosus 'Wood's Pink' - short variety with pink flowers. Resistant to mildew and rust
Aster frikartii 'Monk' - one of the easiest asters to grow. Medium height, blue-purple blooms. Long blooming period
Aster laevis 'Bluebird' - tall, vase shaped. Requires stalking. Lavender color flowers up to one inch diameter
Aster nova-angliae - one of the tallest varieties, blue to purple flowers. It blooms late, even after frosts. The variety 'Purple Dome' is more compact, shorter, with purple blooms.
Aster nova-belgii - short variety that blooms summer thru fall. Reddish purple flowers.

The fading glory of Michaelmas Daisy blooms. Image used under a Creative Commons licence with the kind permission of David Kingham and Flickr