How to Plant, Grow, and Care For Aster Flowering Plants
Are you looking for a bit of fall color in your garden beds? Asters are your answer. These stunning perennials are popular across North America, especially in pollinator gardens. Plant one variety, or choose several of the hundreds in this genus and plant family for a garden full of wildlife and color throughout summer and fall.
Asters are a genus of plants with captivating star-shaped flowers that carpet garden landscapes throughout fall. Asters are easy to grow and are one of the few plants that flower reliably in the cooler season. This can help extend the color of spring and summer longer than most other perennials.
These plants are also low maintenance and produce masses of flowers with very little effort. The flowers come in a wide range of colors, from softer blues and purples to bright, luminescent red. They also attract a wide range of pollinators and are beloved by bees when the other flowers in your garden die down.
With a choice of over 600 plants (either part of the aster genus or previously part of the aster genus still known as asters, but we’ll clear up that confusion later), there is an aster out there for every gardener. Fill your beds and containers with these lively plants for fall interest and a garden full of pollinators for years to come.
Aster Plant Overiew
Plant Type Perennial
Native Area North America, Eurasia
Hardiness Zones USDA 3-8
Season Late Summer and Fall
Exposure Full Sun to Partial Shade
Plant Spacing +/-2 feet
Height 1-8 feet
Watering Requirements Moderate
Pests Aphids, Slugs and Snails, Lace Bugs
Diseases Powdery Mildew, Leaf Spot, Rust
Soil Type Loamy, Nutrient-rich, Well-draining
Attracts Bees, Butterflies, Other Pollinators
Plant With Azaleas, Coneflowers, Hydrangeas,
Plant History and Cultivation
The name aster derives from the Ancient Greek for ‘star’, describing the star-like shape of the flowers. While there isn’t much known about the origins and spread of this popular plant, we do know when they gained their popularity.
Around the 18th century, when plant collecting and studies were beginning to take off, botanists traveled the world in search of new and interesting plant varieties. Asters fell high on that list due to their variety and stunning flowers.
Brought back to Europe from North America, Asters perfectly suited the wilder, more informal cottage garden style exploding around Victorian England. The flowers were grown across the country, becoming somewhat of an obsession. The plants were hybridized and cross-bred to create the dramatic diversity in color and size we have today.
Aster can be a confusing genus. Up until the 1990s, asters comprised over 600 species of plants. That number has since been reduced to around 180 due to the reclassification of some of the plants. Some flowers previously known as asters are now labeled Eucephalus, Oreostemma, or Symphyotrichum, among many others.
However, don’t let the botanical naming conventions confuse you. Most of these plants are still commonly known as asters, even if they aren’t technically part of the aster genus. They also all have similar growing conditions and care requirements, depending on the cultivar.
There are several ways to propagate asters, each producing relatively reliable results. For those who want full control of the growing process, start by growing from seed. Existing plants with plenty of growth can be divided after a few years. Alternatively, you can steal a few cuttings from your neighbors garden (prior permission recommended) and propagate that way.
Propagating From Seed
If you have an existing aster in your garden, collect the seeds after flowering for propagation. The seeds look similar to dandelion seeds – fluffy and light brown. These seeds can then be planted in a seedling tray and started indoors, or planted straight into the garden, depending on the season.
When starting indoors, sow one or two seeds per plug into a tray filled with a pre-moistened suitable growing medium. Seed germinating mixes are available from most nurseries, or you can make your own using coconut coir, perlite, or other airy materials.
Cover the seeds with a thin layer of mix and press down gently to ensure soil contact around all parts of the seed. Mist the soil gently to saturate and place the tray in a warm, sunny spot to wait for germination.
If you’ve planted two seeds per plug, thin the sprouts by removing the weakest performing one. This will ensure you get the strongest plants possible to survive transplanting. A few days before planting, move the tray outside to help the seedlings acclimatize to outdoor weather.
Keep in mind that not all plants grown from seed will look the same. Any hybridized or cross-pollinated cultivars will produce plants different from the parent.
This can make growing from seed an exciting experiment, waiting until flowering season to see what kind of aster you’ll get. However, it can also lead to unpredictable results. The plant you grow may not flower as reliably or may have more problems with pests and diseases. The seeds from the existing plant may also be sterile, preventing you from propagating altogether.
The key to avoiding these issues is knowing what you’re starting with. Check whether that species will propagate well from seed before starting to avoid disappointment later on.
Propagating From Cuttings
Propagating from cuttings is a far more reliable method in terms of keeping the same cultivar. This can be done in spring or early summer to ensure quick growth. Growing over the next year, your cuttings should flower the following fall.
Start by cleaning your shears before use. Any potential disease or bacteria on your tools will inhibit growth and prevent successful propagation. Ensure they are completely cleaned with soap and water or sanitized before you get started.
Remove a stem around 4 inches long from the new soft growth of the plant. Remove the leaves on the bottom half, leaving a few sets of leaves at the top for photosynthesis.
To improve root growth, you can dip the end of the cutting in the rooting hormone. Purchased as a powder, the rooting hormone also prevents potential problems with diseases and aids in developing a stronger root system.
Place the cutting in a pot or tray filled with a mixture of peat moss (or coconut coir) and perlite (or sand) to improve drainage. It’s best to make your soil mix rather than use soil from the garden as cuttings need excellent drainage and garden soil can harbor pests and diseases that prevent growth later on.
Bury the bottom half of the cutting so the leaves are just above the soil line. Water gently or spray the soil with a misting bottle before covering the pot with a plastic bag to increase humidity. To stop the plastic bag from touching the cuttings, hold it up by placing skewers on the edges of the pot.
Move the pot to a warm spot away from direct sunlight. New growth indicates that roots have developed and that the cutting is ready for transplanting.
Propagating By Division
Propagating by division will also produce clones of the same plant. Unfortunately, it will take a couple of years before your asters are ready to be divided, but you will have two or more fully-fledged plants in one go, making it worth the wait.
Division is also necessary after a few years of growth to keep the plant looking its best. As the growth emerges from the middle outwards, the center of the plant begins to look bare and die down with age. Any asters with weak growth or no flowers in the center should be divided to produce two new healthy plants.
Division should begin in early spring, just as new growth begins to emerge. Loosen the soil around the plant with a fork and slowly lift to loosen the roots. Pull the entire plant from the ground and shake the soil off around the roots.
Pull off individual shoots by hand, or pull off groups of shoots for larger plants. If the sections do not come loose, trim the roots in between to free the plants. While trimming, avoid damaging the roots as much as possible to prevent transplant shock. If the center of the plant has no new growth, it can be thrown on the compost pile or discarded.
Replant each of the shoots into pots or out into the garden, leaving plenty of space for new growth. Water well after planting and add a layer of mulch to retain moisture.
If planting from seed, sow into a seedling tray in late winter indoors. Plant two seeds per tray and thin them to one once the leaves have emerged, choosing the best performing seed. In early spring, when all frost has passed, move the seedling trays outdoors to prepare them for planting within the next week.
Seedlings can be planted into the ground throughout spring to flower in late summer and fall. Potted asters from your local nursery will normally be available closer to mid-summer when the plants are almost ready to flower.
Space the plants around two feet apart, with some leeway depending on the size of the chosen variety. Some plants only grow about a foot wide and just as tall, while others spread at least four feet, needing far more space to grow. Check the projected size of your chosen aster and adjust accordingly.
Correct spacing will improve airflow between plants, limiting your chances of encountering pests and diseases. It also limits competition for resources between plants, ensuring each one has adequate space to grow to its full potential. The same distance should also be applied between other plants in the same bed to prevent this competition.
Once planted, water deeply and thoroughly to encourage rooting. You can also apply a layer of mulch around the plants – compost or straw work well – to retain moisture and prevent weed germination.
Planting in Pots
You can sow aster seeds directly into their container for keeping on patios or balconies. Alternatively, repot a nursery plant into a slightly bigger pot, or in combination with other flowering plants for a colorful display.
As the plants don’t have deep root systems, the pot doesn’t need to be too deep. However, it should be wide enough to accommodate spreading.
They should be planted in well-draining, high-quality potting soil. Soil straight from the garden is not suitable for planting in containers as it does not provide enough drainage and can become compacted. It can also harbor pests and diseases that will affect your plants later on.
For the best results, amend your potting soil with coconut coir to lighten the mixture while retaining some moisture. Do not add too many drainage materials like perlite or bark chips as these plants prefer consistently moist soil.
How to Grow
When growing Asters, there are many important factors to consider. You need the right light, watering frequency, soil type, climate, temperature, and fertilizer. Missing any crucial element won’t allow your Asters to grow to their full potential. Let’s take a look at each!
Asters perform their best and flower the most when planted in full sun. Some types of asters can handle a bit of shade, but too little sunlight will prevent flowering and stunt growth.
Extra sunlight also speeds up evaporation of any water left on the leaves and flowers after rain or watering, limiting your chances of disease.
Asters can be picky when it comes to watering. Water too much and the plant may lose leaves or wilt, water too little and the plant becomes stressed, preventing flowering. The standard advice of at least one inch per week (either rain or watering) is recommended, but you will need to keep an eye out on your plants’ performance for signs of stress.
When planting many asters in a group, drip irrigation systems keep moisture content in the soil consistent. It also limits problems with disease as the water is delivered straight to the soil and doesn’t land on the leaves or flowers.
Generally, asters prefer soil on the moist side and do not appreciate being left to dry out. Water evenly and consistently for the best performance.
Asters, like most perennial flowering plants, prefer loamy, well-draining soil. Poor quality soil should be amended with plenty of compost before planting, as these plants love nutrient-rich, moisture-retaining soil. Avoid planting in sandy soil which does not retain moisture well. Slightly acidic soil below a pH of 6.8 is best for improved flowering.
When planting in containers, use a high-quality potting mix to prevent problems with nutrient deficiency and drainage. Heavier soil can be amended with coconut coir and perlite to improve drainage. However, don’t add too much, as these plants prefer soil on the moister side.
Climate and Temperature
Asters prefer cooler weather and grow best in USDA Zones 3-8, depending on the variety. Cooler summers with high rainfall provide the plants with everything they need without too much input from you. Cooler weather also improves flowering later on in the season.
These plants are frost tolerant for short periods and don’t mind the cold over winter. Their foliage will die back in fall and can be pruned to promote new healthy growth the following spring.
Asters are not heavy feeders but will flower more reliably when fertilized from spring into summer. Use a slow-release all-purpose fertilizer once in spring and summer to last the rest of the season, or apply a flowering-specific fertilizer according to the instructions on the packaging.
Avoid overfertilizing, especially once the plants begin flowering. Rather than rewarding you with more blooms, they may react to overfertilization by stopping flowering.
A layer of compost applied over the soil as a mulch will also improve nutrients in the soil over the seasons, aiding soil structure at the same time.
Asters are not particularly high-maintenance plants. They will flower and grow better when pinched and deadheaded occasionally in late spring or early summer, but in the right conditions, should grow fine without the haircut.
Pruning once the plant has finished flowering is recommended. This removes dying leaves and spent blooms, keeping the plant tidy and limiting problems with diseases that could cause plant death. However, some gardeners choose to leave the leaves as is to protect tender growth in winter. The choice is up to you.
Apply an organic mulch layer around the plants soon after planting and keep replenishing as they grow. This will help retain moisture in the soil and keep weeds from taking over your beds. Ensure the mulch does not touch the foliage or the stems as this can result in rotting.
If you’re keeping asters in your garden long-term, dividing every few years is recommended. This will improve growth, promote airflow, and provide you with more blooms in the long run. Planted in the right conditions, asters can be divided even sooner, but around 3 or 4 years is the standard.
The most popular asters across North America are now botanically no longer asters. These include New England asters, now Symphyotrichum novae-angliae, and New York asters, now Symphyotrichum novi-belgii. But, there are also many other asters commonly found in home gardens, native to different parts of the world.
For a pop of pink and purple color, try ‘Purple Dome’, a compact New England aster growing 18 inches tall. ‘Alma Poetschke’ is another popular New England aster with intense pink blooms that make a colorful statement in fall.
Those preferring asters with a muted blue tone can try a blue aster variety, like the ‘Sky Blue’, ‘Sapphire’ or ‘Blue Lagoon’ for softer blueish-purple flowers dotted across your garden beds.
Frikart’s aster, hailing from Europe, blooms early and for a long time, creating interest across the seasons. It is also one of the best asters to propagate by cuttings, with a high success rate.
Pests and Diseases
Asters are susceptible to quite a few pests and diseases that you should be on the lookout for.
A few common garden diseases affect aster foliage. Powdery mildew is encountered most often, but you may also come across rust. Stop these diseases from taking over your plants by keeping water off the foliage and removing all debris around the plants.
Leaf spot and stem canker are less common issues. These diseases are not easily removed and should be dealt with as soon as they are discovered. Prune off all affected foliage and discard it to prevent the problem from spreading to other parts of your garden. Keep an eye on the growth and continually prune until the issue is resolved.
Aphids, the tiny bugs that tend to take over your garden, also enjoy snacking on asters. Keep them off your plants by removing them by hand, or applying a horticultural oil if the problem is uncontrollable.
Slugs and snails may also become an issue. They munch on the leaves of the plant, leaving tell-tale signs of their damage. To make matters worse, slugs and snails are most active at night, making them incredibly difficult to remove by hand.
Instead of arming yourself with a torch and hunting them at night, install a simple beer trap. Dig a tray or bucket into the soil and fill it with beer. The snails will be attracted to the beer and will stay away from your precious asters, and the rest of the plants in your garden.
Also keep an eye out for lace bugs, nematodes, mites, and leaf miners.
If treating your plants with any products to prevent pests and diseases, beware of how it will affect other wildlife. Asters are great pollinators, attracting many bees and butterflies to your garden. Harmful products will also harm them too and should be avoided.
With the diversity within the aster genus (and those plants previously part of the aster genus) comes a great diversity in uses.
Shorter aster varieties are suitable as filler plants in garden beds or containers. Dotted amongst other plants, they highlight the best of their surrounding neighbors, stealing the show in summer and fall when they flower.
Later blooming varieties can also be used to add color once your spring and summer perennials stop flowering.
Some asters can grow several feet tall, suitable for the back of flower beds as a backdrop. When interplanted with other tall blooming plants, the flowers mix in an informal display reminiscent of a wildflower field.
Taller plants can be combined with suitable groundcover plants. This will help the soil retain moisture, limiting the need for mulching. These living mulches also keep weeds down while adding ornamental value to your beds.
For a stunning carpet of color, asters look fantastic when planted together. If you have the space, dedicate a whole bed to these perennials, using a mixture of short and tall varieties in a wide range of colors. The flower shapes provide harmony and uniformity, while the rainbow of color and size adds interest to your garden.
These masses of asters will also attract tons of pollinators to your garden. Butterflies, bees, and other garden friends are drawn to the enchanting colors and will stick around throughout the flowering season.
Besides their benefits out in the garden, asters are also commonly used in the floral industry. They make great cut flowers, and can even be dried for a long-lasting bouquet.
Frequently Asked Questions
What do asters smell like?
Aster flowers across the varieties have little to no scent. Some plants in the aster family have leaves that release a slight scent when crushed, but it is not a major feature of these plants. Even the confusingly named Aromatic Aster (Symphyotrichum oblongifolium) has no scent.
What do asters symbolize?
Asters are said to symbolize love, wisdom, and faith in the floral world.
Will asters survive winter?
Asters are perennial plants that will survive winter in USDA Zones as low as 3. The foliage and flowers will likely die back in response to the cold, but growth will re-emerge in early spring once temperatures warm.
Will asters grow in shade?
Asters are not suitable for shade gardens. While they can tolerate some partial shade, the growth and flowering will be inconsistent. If your stems are tall and lanky, or if your plant is not flowering reliably, it’s best to move the plant into a sunnier spot.
Are asters poisonous to cats?
Asters are completely safe for cats, whether planted out into the garden or brought indoors as part of a bouquet. They are also non-toxic to dogs and many other common pets.
When do asters flower?
Asters flower at different times and for different periods depending on the variety. Most will flower sometime from late summer to early fall.
Why are my asters turning brown?
Asters can turn brown for a number of reasons, one of the most common being inconsistent watering. These plants are very moisture sensitive and need consistent watering and moist soil to thrive. Any deviation from their regular watering schedule, especially in summer as the heat kicks in, may cause the stems and foliage to turn brown.
Other problems include issues with pests and diseases. Examine your plants carefully for signs of an infestation and treat accordingly to resolve the problem.
What is the difference between asters and mums?
Chrysanthemums, commonly called mums, are part of the aster family Asteraceae. However, they have a different genus to asters, or those formerly known as asters, and are different plants. To get technical, you could say mums are a type of aster, but not all asters are mums. These plants both flower around fall and make great companion plants.
These versatile, low-maintenance plants will not disappoint in your garden. Whether grown from seed or propagated by division or cuttings, you will be rewarded with carpets of blooms in whatever color you choose.
With a close eye on water levels and a continuous check for pests and diseases, your asters will give you no problems. They’re bound to become your favorite garden perennials soon after planting.