Perennial asters grow on mounding or upright plants with lance-shaped foliage, producing autumn blooms in shades of blue, red, white, and pink. The flower is welcome in the fall garden to complement mums, which aren’t available in blue shades.
Because it is smaller, drastic pruning is unnecessary and can weaken or deform the plant. Light pruning, however, is advantageous. It removes parts of the plant that are no longer beneficial, allowing the plant to distribute energy to healthy stalks and blooms.
Zones 3-8, depending on variety
Asters appreciate soil on the slightly acidic side, with a pH ranging from 5.8 to 6.5. If your soil is alkaline, you can correct it by adding organic matter such as well-rotted manure, leaf mold, or compost.
Although asters are common in garden centers in the fall, when they are visually appealing, the plants need some time to develop a root system before the ground freezes if you expect them to come back in the spring. Plant asters as soon as they’re available in early fall, and keep them moist during any late hot spells to help them settle in.
Gardeners often blame the death of an aster the following year on hardiness issues, but many asters perish over their first winter due to heavy soils and poor drainage. If you have heavy clay in your flower garden, plant your asters in raised beds or consider double-digging the soil.
- Fertilizing. Asters are moderate feeders, and they appreciate a balanced flower fertilizer given twice a month from spring until the blooms begin to open. Excessive nutrients can shorten the blooming time, so stop fertilizing asters in August.
- Watering. As is the case with many flowers with wildflower heritage, asters are somewhat drought tolerant; certainly more so than mums. However, long periods of drought cause yellow foliage, so provide supplementary irrigation to equal one inch of rain per week during dry spells.
- Disease. Rust and powdery mildew disease can affect aster foliage. Follow proper plant spacing to improve air circulation, and avoid overhead watering to prevent these problems.
- Pruning. Pinch back the tops of the asters by 6 to 8 inches before mid-July. This will induce bushier plants and give the asters a longer blooming period.
- Cutting. Cut down the aster after the flowering season. This will prevent the perennial from seeding its own plot and leading to overcrowded beds in the spring.
Choose late-flowering purple asters to extend garden color until well into the autumn. Their mounding growth is ideal as garden borders, or planted in masses to be the focal point of any flower bed. Use them to invite butterflies to your landscaping beds into the fall. They work well mixed with other fall asters, like tall-growing, blue-flowered and purple-dome asters, all late bloomers in a rainbow of whites, pinks and blues.
Asters make a good cut flower for fall arrangements. Cut the flowers late in the evening to avoid contact with avid bee visitors. Take stems when about 1/5 of the flowers are open for the longest vase life.
Because asters and mums bloom at the same time, you can plan several attractive garden schemes with these two fall perennials:
- Plant blue asters beside yellow mums; these opposites on the color wheel pop.
- Combine purple asters and white mums in a garden container.
- Pair the dainty blooms of a pink aster variety with the larger double flowers of a pink or purple mum for textural interest.
See all varieties