Those seeking to pump up the color in their flower beds should consider planting China asters (Callistephus chinensis), also called summer aster. The annual is hardy throughout the U.S. and even black-thumb gardeners should have success growing these flowering beauties.
Depending on the cultivar, summer asters produce flowers resembling chrysanthemums or peonies; they can be double or single and up to 3 to 5 inches across. Flower colors range in colors of pink, red, white, blue, purples, and yellow, so there's a color available for everyone's taste. Flowering starts in late summer and continues into early fall.
Oval foliage is green and toothy on its edges. Depending on the cultivar, plants range in size from 12 to 36 inches tall and generally half as wide as the plant's height. Plants have a moderate growth rate.
Common Cultivar Types
Gardeners have quite a few choices when it comes to the different types of cultivars available through online seed companies like Johnny's Select Seeds and Eden Brothers, or at your local garden center. Commonly found cultivars and their characteristics include:
Tower Custom Mix
The tower custom mix produces large blooms resembling a peony and come in multiple colorations. This is a large plant averaging around 32-inches in height.
These gorgeous blooms are semi-double flowers ranging in an array of colors. Plants average around 24 inches in height.
The single mix is, as the name implies, single flowers with large yellow centers in multiple colors. Plants range from 1 foot to 3 feet tall.
The flower is a profuse bloomer and makes a colorful addition used along borders, in cut flower gardens, mixed gardens, as a filler and taller cultivars make a good backdrop plant. They also perform well used inside containers. According to the ASPCA, China aster isn't toxic to pets, so no worries if Fido has a hankering for some flowers.
If using as cut flowers, snip off a long stem with sterilized pruning shears. Place the cut flower stems in a vase of water with added florist preservative. Do not place the foliage in the water as it decreased the life of the flower due to rot. Change the water with fresh every few days and the flowers should last for a week or two.
Preferred Growing Conditions
For the best growth and performance, grow summer asters in rich soil that drains well, but kept moist through regular applications of water especially during hot and dry weather. The plant has a low tolerance to drought conditions. Situate in a full sun or a partially shady location in the landscape.
Work compost or organic material into the planting site before planting the asters if your soil lacks organic nutrients. Work the substance into the native soil to a depth of approximately 6 to 8 inches.
Planting the Flowers
Whether planting transplants purchased at your local garden center or seeds, it's important to allow enough room around plants for air to circulate. Planting them too close together promotes problems with disease and pests. To help the soil retain moisture and cut down on weed growth, apply several inches of mulch around the plants.
China aster grows easily from seed and usually germinates in one to two weeks when temperatures range around 70 degrees F. When planted from seed, it takes approximately three to four months for plants to reach maturity and start blooming. For ease in transplanting and less disruption of the root system, plant the seeds in peat pots and then transplant the entire pot into the garden once the plant reaches 4 to 5 inches in height.
If you plan to display your flowers inside a container, you can plant the seed directly into the container you plan on using. Be sure to thin the seedlings once they germinate so they aren't overcrowded. A 3-gallon container is large enough for one plant to grow properly and allow the root system enough space to spread out.
- Fill a peat pot full of rich potting mix that drains well. Settle the soil in the pot by watering.
- Sprinkle the seed on top of the soil and lightly cover with 1/8-inch of potting mix.
- Moisten the soil again with water and place the peat pot in a sunny location or if started indoors, place the peat pot in high light location or in a sunny window.
- Place the seedlings into a prepared garden location spacing each plant 1 to 2 feet apart for proper air circulation and water well.
Depending on where you live, you might be able to purchase already started and mature plants at your local plant nursery. Nursery transplants are generally already blooming and ready to put on their riot of color within the garden.
- Dig a hole in a prepared garden bed that is deep and wide enough to plant the summer aster at the same height it was growing in its container.
- Carefully remove the plant from the nursery container, being careful not to disturb the root system.
- Place the transplant into the hole and pack the soil around it. Water in well.
Unlike many flowers, it's not necessary to deadhead spent blooms, but it won't hurt the plant or flowering if you decide to remove dead flowers. The biggest part of continued care to keep China asters growing well is making sure the planting site doesn't remain constantly dry from lack of water. Depending on your local weather conditions, plants may require applications of water several times weekly. Plants grown in containers may need daily water.
Pruning isn't required other than to remove dead or diseased branches. To prevent pest or disease problems, keep the planting site free of all weed growth.
To keep plants healthy and blooming, fertilize summer asters with a water-soluble blend of a 10-10-10 fertilizer. Use a hose end sprayer or watering can and pour the mixture over the entire plant. Apply every four weeks during the growing season.
Pest and Disease Problems
Like most plants in the aster family, China aster is susceptible to a host of pest and disease problems. Planting in a location where asters haven't previously grown, keeping the area weed-free, and not planting the asters butted together allowing proper air circulation goes a long way in keeping the plants healthy.
The most common pests are leafhoppers, mites and aphids, with leafhoppers being the most serious.
- Leafhoppers: Leafhoppers are small winged insects usually around 1/2-inch long and depending on the type, range in colors of green, yellow or brownish. The insect feeds on the China aster by sucking the plant's juices and transmitting the disease aster yellows. Some types secrete honeydew, which then can lead to the black fungus sooty mold. Damage includes leaf curling, yellowing and plant death. The insect is hard to control; the best method is keeping the flower bed free of weed and grass growth and removing diseased plants as prevention.
- Aphids: Aphids suck juices from the China aster causing stunted growth, curling, and yellowing and can lead to plant death. Aphids congregate on flower buds, foliage and young stems. Usually a strong blast of water knocks the insects from plants. In the event of a large infestation, spray the plants weekly with an insecticidal soap.
- Mites: Mite damage shows by the entire plant yellowing, which leads to curling foliage and if an infestation is heavy, eventual plant death. Mites are very small and usually whitish, but are easy to identify as they create a fine, white webbing over the plant similar to a spider web. Blasting the China aster with a strong blast of water usually takes care of small infestations, but large infestations require treating with weekly applications of an insecticidal soap.
The flower is susceptible to the same disease problems as others in the family. Prevent most issues by changing planting sites each year, raking up decaying leaf debris, keeping the planting site free of weeds, and not composting pest- or disease-ridden plants.
- Fusarium Wilt: A soil borne disease that affects the vascular system eventually killing the plant. It causes leaf curling, yellowing of foliage, root rot, and collapse of the plant. Once the aster is infected, the best course of action is to remove the plant and discard. Prevent the problem by making sure the soil drains well, keeping the planting site free of debris, don't water overhead or planting on a raised bed. Don't replant in areas where fusarium wilt has been a previous problem.
- Aster Yellows: Aster yellows is a tiny organism transmitted through leafhoppers and infected plants are dwarf, flowers turn leaf-like, greenish-yellow, stringy, and upright growths appear around the plant's base. Pull out infected plants and destroy. Prevent the problem by keeping the flower bed free of weed and grass growth that attracts leafhoppers.
Some Like it Hot
When many plants have finished flowering by the hot days of late summer, China aster just begins putting on its colorful show. Between the many choices in flower shapes, colors and plant size, you probably won't be able to resist filling the garden with several varieties.