Growing Asters: Tips for Adding Color to Your Garden
After summer flowers have faded and before winter bloomers appear, asters light up the garden with their cheery, daisy-like flowers. Native to temperate regions in the Northern Hemisphere, they grow well in our mild Southern California weather.
“Although asters come in a wide range of colors and sizes and are vigorous growers, they are uncommon in many gardens,” says John Whittlesey, owner of Canyon Creek Nursery in Oroville, a mail-order company that specializes in uncommon perennials, including more than 20 perennial aster varieties.
Asters range in size from small, 6-inch-high mounding bedding plants to 6-foot-tall giants that can grow several feet wide. Flower colors include white, blue, lavender, yellow, pink, and purple.
Some of Whittlesey’s favorites include ‘Bill’s Big Blue,’ which grows to 5 feet tall and 3 feet wide. This makes a great cut flower with its sturdy, erect stems topped with long sprays of medium-blue flowers.
A. pringlei ‘Monte Casino’ was developed for use as a cut flower in Holland. It grows 4 to 5 feet tall and has airy sprays of white flowers resembling baby’s breath that are used as filler in bouquets.
Popular Aster Varieties
Here are some varieties of asters that thrive in Southern California:
- A. Cordifolius ‘Little Carlow’: Tolerates partial shade and grows 3 to 4 feet high with dark violet-blue flowers.
- A. Lateriflorus ‘Prince’: Has deep purple leaves during the summer and is covered with mauve-pink flowers in the fall.
Planting Tips for Asters
Now is a great time to transplant asters, many of which will bloom into November. Follow these planting guidelines:
- Sun Exposure: Most asters prefer full sun, though some varieties like divaricatus and cordifolius tolerate partial shade. Keep in mind that asters are dormant during the winter months.
- Soil and Watering: Asters require regular watering. If planting in a dry area, amend the soil with 25% compost to improve its water-holding capacity. Plant asters at the same height they are in their containers and space them 24 to 30 inches apart.
- Container Growing: Asters can thrive in containers. Use a pot that’s at least 12 inches in diameter, high-quality potting soil, and a slow-release fertilizer.
- Watering: Keep the soil moist but not soggy.
- Fertilizing: Fertilize ground-grown asters monthly with an all-purpose fertilizer during their growth period, generally from March through November.
Care and Maintenance
- Pruning: Avoid pruning asters during their active growth period, especially in the summer. Pruning won’t improve blooming and may reduce the number of flowers in the fall.
- Protection from Winds: Shelter asters from strong Santa Ana winds, which can damage the plants. Staking taller varieties may be necessary.
- Pest Control: Asters are generally pest- and disease-free but may occasionally develop powdery mildew in late fall. The best prevention is to avoid overhead watering.
- Dormancy and Cutting Back: After flowering, asters go dormant. Cut them back to the ground, leaving a small amount of basal foliage. In spring, the plant will regrow.
- Dividing Asters: To maintain vitality, divide asters every two to three years in February or March. Dig up the plants, select the strongest pieces, and replant them in the same location.
Planting Aster: Info Box
Planting Aster (Compositae – Perennials – All zones)
- There are more than 600 species of true asters, ranging from 6 inches to 6 feet high.
- Transplant asters at the same height as their original pots.
- Ensure the soil remains moist, amending with 25% compost if the soil is dry.
- When planting multiple asters, space them 24 to 30 inches apart.
Canyon Creek Nursery
3527 Dry Creek Road, Oroville, CA 95965
(530) 533-2166
Catalog $2.
