Many gardeners, myself included, focus on spring and summer blooming flowers to help us emerge from the cold, dark winter. We plan our summer cutting gardens, sometimes forgetting what happens in the fall when our short-lived annuals fade.
Enter the China aster. These funky, bright flowers bloom just when the rest of the garden may be dropping seeds or turning brown, blooming alongside dahlias. While the asters you see for sale outside the grocery store may not excite you, China asters certainly will!
Let’s get into how to plant, grow, and care for them.
Overview
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What Is It?
These cool-weather flowering annuals make a great addition to garden borders, beds, and patio containers. They make excellent cut flowers and come into bloom when summer gardens are fading. The word aster means “star” in Greek, which refers to its star-like shape and brightness.
Appearance
China asters offer a diverse array of colors and bloom sizes.
Colors range from shades of white, pink, yellow, red, violet, purple, and peach with yellow centers. Blooms can be three to five inches in diameter in single, semi, or double blooms. Height and shape vary too; some are dahlia-like with multi-layered petals, some are daisy-like with more flattened disc-shaped heads, while others are spiky and airy or pom-pom shaped.
Plants range from one to three feet tall and can be single or multi-bloom stems. They are sometimes confused for chrysanthemums, which are close relatives.
China Aster Versus Other Asters
This species is annual, while other asters are perennials.
China asters are annuals, whereas many other types of asters are perennial, returning each spring.
How to Grow
These flowers are fairly low-maintenance and easy to grow.
Sunlight Requirements
Provide full sun to partial shade for best growth.
China asters should be planted in full sun to partial shade. They will appreciate some afternoon shade in especially hot climates.
Water Requirements
Maintain soil moisture by watering twice weekly without causing sogginess.
Water regularly, about twice per week, and ensure the soil remains moist but not soggy. If you’re unsure whether or not watering is necessary, check the top one to two inches. If they’re dry, water again.
Soil Requirements
Provide soil with good drainage and fertility.
Soil should be well-draining and fertile, with a pH of 5.5-7.5. China asters like aerated soil that’s rich with organic matter. Amend bedding soil with compost if necessary. This has a dual purpose of providing nutrients, and retaining water.
Mulch
Mulching around the base of plants retains moisture and controls weeds.
China asters are shallow-rooted, so mulching around the base will help the soil retain moisture and keep weeds at bay. Organic mulches are great, as they break down over time and feed the soil with nutrients.
Climate and Temperature Requirements
Cool-season conditions and full sun result in prolific blooms.
These cool-season bloomers will do best where summers are mild. While they thrive in full sun, consistent temperatures over 80°F (27°C) and hot sun will cause them to cease blooming. Flowering should return in the fall when temperatures decrease.
They can tolerate near-freezing temperatures and even a light frost in the fall, but take caution when planting seedlings in the spring by waiting until after the last possible frost date before transplanting.
Fertilizing
Fertilize them with a 10-10-10 organic fertilizer every 3-4 weeks when budding.
Feed them an organic, well-balanced fertilizer such as a 10-10-10, beginning when the soil warms and buds are starting, and repeat every three to four weeks. Stop fertilizing when the plant is putting out fewer blooms, as it won’t make much of a difference at that time.
Liquid fertilizers are better suited to this frequent feeding, as opposed to granular fertilizers. You can start the season with a granular fertilizer, and use diluted liquid fertilizer in subsequent feedings. Note that organic fertilizers are more bioavailable to plants than synthetics are.
Harvesting
Harvest in the morning when fully open and before seeds set.
Pick asters when blooms are about halfway open for the best vase life. Much longer, and the petals will brown. Harvesting and deadheading will encourage more blooms and keep the plant looking its best. Spray varieties should be harvested when about a quarter of the blooms on the stem have opened and you can see color.
When planning to dry them, harvest them in the morning when they’re fully open and before the seeds are set. While they can be used in dried bouquets and crafts, they don’t keep or store well after one season.
Pruning
Encourage bushiness and side shooting by occasionally pinching back the plant.
No pinching back or pruning is necessary. However, pinching back may encourage a bushier plant and side shooting. If blooms slow down in the summer due to extreme heat, you may cut it back to encourage additional blooms in the fall.
Support them when they’re young to prevent the eventual blooms from causing them to flop over.
Collecting Seeds
Dry and store withered flower heads in a cool place.
When you notice flower heads’ petals withering away and turning brown, grab some snips and a brown bag. Toss the heads into the bag and allow them to dry inside in a cool, dry place for a few weeks.
Gently separate the seeds from any remaining silks from the seedhead and store them in an airtight container, glass jar, or brown paper seed bag. Remove soft seeds or any that show signs of decay. Label them with the year and variety for easy identification.
Collecting seedheads as they brown will keep self-seeding to a minimum.
Propagation
China aster plants are easy to grow and most often started from seed.
Starting From Seed
Start seeds indoors six to eight weeks before the last frost.
When starting from seed indoors, sow seeds six to eight weeks before your region’s last anticipated frost. Sow seeds just below the soil surface in 72-cell trays or containers and keep them in a warm place to germinate. Don’t allow the soil to dry out. Germination may take up to two weeks.
Step up the seedlings as needed before transplanting, and do not allow them to become rootbound. As seedlings, these cool-weather-loving plants are cold-sensitive, so cover them if necessary. Establishing them early will allow them to grow nice, tall stems.
If sowing seeds directly outdoors, do so once the soil temperature is at least 65°F (18°C) and when the danger of frost has passed.
Self-Seeding
Annual self-seeding can be managed by removing some seeds from the soil surface.
When left in the garden, these annuals will readily self-seed. Some seeds can be removed from the soil surface in the fall to avoid a large amount of germinating seedlings in the spring.
Planting
Ensure the risk of frost has passed and the soil has warmed before planting out. Then get to work sowing some of the best flowers you can grow!
Hardening Off
It is crucial to adapt seedlings to outdoor conditions before transplanting them.
Allow seedlings to acclimate to outdoor wind, sunlight, and overnight temperatures for a week or two before transplanting. Do this in phases of one hour one day, then two the next. Once they have experienced a full day outdoors, they’re ready for planting. Cover if needed.
Spacing
Sizes vary greatly depending on the chosen cultivar.
China asters vary greatly in size and shape. The particular cultivar you select will determine how much space they’ll need. Give them between six inches and three feet. This will also depend on your garden’s aesthetics and style.
Transplanting
Planting deep into the soil promotes strong root systems.
Transplanting China asters a bit deeper than usual may allow them to form a strong root system that will provide them with additional support needed to withstand the heavy blooms.
Transplant once the risk of frost has passed and the soil has warmed. Depending on the variety, space them at 8-12 inches or more to allow for proper airflow and access to nutrients.
Popular Varieties
It’s hard to choose a favorite, but here are some popular varieties. No matter which you choose, care is relatively similar.
‘Bonita Top Blue’
These deep purple asters have plush, abundant blooms.
‘Bonita Top Blue’ Asters feature dense clusters of saturated purple blooms atop sturdy stems. They are excellent for cutting and have a long summer bloom period.
‘Lady Coral Chamois’
This pale coral option offers a vase life of 7-10 days.
This romantic and feminine, soft peach blush option has ruffled slightly incurved petals, resembling a popped balloon. Each stem offers lots of blooms and grows to be two to three feet. Vase life is 7-10 days, and plants mature in 110-120 days.
A bunch of these with some feverfew or mountain mint would make a delicate bouquet for a baby shower or kid’s birthday party.
‘Milady’ Series
This is ideal for low-maintenance gardens in borders or containers.
This dwarf blend is 10-12 inches tall with busy, wilt-resistant three-inch blooms. Colors are a mix of white, lavender, pink, rose, and carmine. They’re easy to grow and perfect for a low-maintenance garden along borders or in containers. They’ll bloom all summer and fall.
‘Lady Coral Lavender’
This late-blooming China aster cultivar boasts silvery lavender blooms.
This cultivar is a stunning, almost silvery lavender shade with 2 ½ – 3 ½ inch blooms. ‘Lady Coral’ Lavender blooms a little bit later than most, taking 115-125 days to mature, and will help extend your cutting flower season. Plants reach up to 30 inches.
Plant Uses
China asters can be incorporated into virtually any type of garden. They’ll add textural interest and color to your fall garden.
Design Ideas
Asters in various soft and bright shades enhance cottage gardens.
China asters in pale peaches, silvery lavenders, and white are perfect for cottage gardens, and the brighter carmine and violet options complement late-season ornamental grasses, salvia, and snapdragons.
Garden Design
Pair with late-blooming flowering annuals like marigolds and ornamental grasses.
Since China asters bloom a bit later than most flowering annuals, pair them together to keep the color in your garden going strong into fall. Possibilities include marigolds, various ornamental grasses, strawflowers, late-season sunflowers, brown-eyed Susans, and hydrangeas.
Common Problems
Prevention and swift action, along with proper soil fertility and crop rotation, will help decrease the risk of issues that can cause browning and wilting.
Pests
Watch for aphids, spider mites, and thrips.
These cheerful flowers are generally easy to grow, but they can sometimes be subject to pest infestations.
Aphids suck the juices from leaves and stems. Populations can get out of control quickly, and their sticky, sugary waste attracts ants which opens the plant up to additional issues like fungus. A strong blast of water usually removes aphids, but that’s a temporary fix. Neem oil may prevent them from landing on your plants, and garlic spray may repel them. Plant dill and yarrow nearby to attract ladybeetles, a natural predator of aphids, to control populations.
Spider mites cause damage to plants by sucking the juices from the leaves. Annual plants are typically at a higher risk of extreme damage. Attracting natural predators like green and brown lacewings, minute pirate bugs, and ladybeetles is the best way to decrease populations of spider mites.
Leafhoppers commonly transmit bacteria that can cause aster yellows. Cover your plants with insect netting immediately upon transplanting and remove it once the plants have started to flower and need pollination.
Thrips can cause spotted or misshapen flowers and silvery streaks on ornamental leaves. Controlling thrips is a matter of limiting the areas they prefer to lay eggs, such as fallen leaves and stems and random plant debris. When pulling weeds, pruning, and thinning plants, remove all debris immediately.
This highly destructive, iridescent, ½-inch-long pest emerges in early summer, and you’ll know they’re present if you start to see lots of skeletonized leaves. They reproduce often and heavily, and if populations get out of control of this hungry beetle, they’ll move on to the next plant they enjoy feeding on, the list of which is long. Planting geraniums nearby may cause paralysis for a few hours. Sometimes, they recover, but often, they’re found and eaten by predators.
China asters are deer-resistant and non-toxic to pets and humans. They are a great source of food for late-season pollinators, particularly long-tongued bees.
Diseases
Organic controls are recommended.
China asters don’t react well to most pesticides, so organic controls should be used. If you do choose pesticides, test them out on one or two plants and watch for a negative reaction before spraying them all.
This is one of the most common issues, which is caused by a phytoplasma pathogen. It lives in the vascular system of the plant or within the insect that’s transmitting it from plant to plant. Eventually, it will make its way through the whole plant and will quickly spread to nearby plants. Use insect netting to keep leafhoppers out who may transmit the disease.
Symptoms include stunted and deformed growth, discolored leaves, sometimes red, thin, weak stems, and small flowers. There is no known cure for aster yellows. Infected plants should be removed and destroyed. This bacteria may affect perennial weeds. All garden debris should be removed before winter.
When infected, gray fuzzy spots will form on water-soaked and browning flowers. Botrytis cinerea favors wet, cool conditions. Use drip irrigation and water plants in the morning so no moisture is left when night falls, and remove all plant debris from the garden. Provide ample airflow and space between plants.
Symptoms include leaves browning and wilting. Unfortunately, it is not treatable. Fusarium oxysporum f. sp. callistephi can live in the soil for many years, so rotating crops is crucial. Always buy seeds, compost, and amendments from reputable sources as it’s often seed-borne.
Caused by a soil-borne fungus, this disease will attack all parts of the plant, beginning by weakening the stem at the soil line. Symptoms are worsened when your soil is not well-draining or particularly wet. Avoid overwatering. You may catch this disease in time if you happen to notice soft stems, browning leaves, or wilting, but typically, it’s too late once you notice a problem. Moving the plant to a drier area may resolve the issue.
Frequently Asked Questions
Under ideal conditions and with proper care, they’ll bloom for six weeks. There are longer-blooming cultivars available that may bloom for two months in the summer.
It’s not required, but it may create a bushier and more compact plant and encourage more blooms.
While they are an annual flower, they self-seed, sometimes quite heavily. To avoid them becoming invasive, remove some seedheads or rake seeds out from the soil surface when cleaning up your garden in the fall.
Final Thoughts
China asters are beautiful and easy-to-grow annual flowers. If you have some extra space in your garden and are looking for something bright and spunky, I hope you give them a shot!
