How to Grow Asters

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The gorgeous Aster is a fantastic low-effort addition to your garden. Its name originates from the Greek word for star, but also goes by many other names, with September flower, Michealmas daisy, and frost flower being just a few of them.

Asters vary in color, size, and ease of care depending on the variety that you grow. You’ll never find an aster flower with bright orange or yellow petals — they come in blue, purple, white, red, or pink. But no matter the color, it’s easy to identify them by their bright yellow center composed of many flowerets.

In the floral industry, asters are one of the most popular flowers to grow and sell. This is due to their versatility and long life once cut. They’ll last over a week before wilting.

They’re a fantastic addition to the garden, especially in summer. So let’s figure out how to grow them!​

Aster Information

Botanical Name

Aster spp.

Plant Type Flower
Sun Exposure Full or partial sun
Soil Preference Loamy
Soil pH Varies
Hardiness Zone(s) 3-8
Flower Color Varies, common colors include red, pink, white, purple
Bloom Time Summer or Fall
Unique Qualities Attracts butterflies, bees love them

Types of Asters

Asters come in many varieties. When you’re just starting out, it’s hard to tell the difference between them all — but it matters, because many grow much taller than others and have very different flower appearance.

The two most common types of aster are New York and New England. Not surprisingly, they’re also hard to differentiate.

 

New York and New England Aster
New York and New England Aster (source | source)

New York aster has both tall and short varieties, but they tend to clump in the 2-4′ range. Some New York aster reaches upwards of 4′ tall! The stems are thinner than New England aster, and the leaves are usually smoother.

New England aster grows to be around 3-4′ in height, though you can get varieties that grow either shorter or taller. In contrast to New York aster, it has hefty stems with leaves that are covered in hair. The flowers are much denser as well.

Other less-common types of aster include:​

Heath Aster
Heath Aster. source

Heath aster is my favorite variety. It grows to 3-4 feet and its leaves are very small and thin. What makes it so special is the multitude of small white flowers that show up as it blooms.

Calico Aster
Calico Aster. source

Calico aster and heath aster are difficult to tell apart. The giveaway is that calico only grows to 1-2 feet and the flowers only bloom on one side of the stems instead of all of the way around.

Aromatic Aster
Aromatic Aster. source

As you might imagine, aromatic aster gets its name from the smell it produces when you touch it. It’s quite a nice smell, so if you get joy out of smelling the flowers in your garden you may want to go with this variety. The flowers are a bit thicker-leaved than either heath or calico aster.

Smooth Aster
Smooth Aster. source

Smooth aster has a unique leaf shape that is more oval or egg-shaped at the end when compared to other varieties. As you might imagine, the leaves are also quite a bit smoother than most other types of aster.

Heart-Leafed Aster
Heart-Leafed Aster. source

The more common name for this type of aster is heart-leaf. It is strikingly different from the varieties we have covered already, due to the thin stems and darker centers.

Planting Asters

No matter which propagation method you used for your asters, spacing them correctly is important. Too close and you run the risk of competition for water and nutrition.

If you’re growing a miniature aster cultivar, you can get away with half a foot between each plant. If you’re growing one of the taller varieties, you’ll need to increase spacing to at least a foot (and up to two feet on the tallest varieties).

Asters will do well in “OK” soil, but they prefer loamy soil that drains very well as they’re moisture-sensitive. If your soil doesn’t drain well, add in sand, vermiculite, or perlite.

They require at least partial sun, but prefer full sun for optimal growth.

Caring for Asters

​Asters are quite easy to take care of, with little maintenance required to grow a healthy, beautiful bunch of aster flowers. But, with a little extra effort your aster plants will thrive and produce a much more vibrant set of flowers.

Every spring, amend your soil with a very thin layer of organic compost​. Add 1-2″ of high quality mulch on top for protection.

If you live in a drought-ridden area and get less than an inch of rain per week (4 inches per month), then you will need to water your aster plants during the hot summer months. Be careful not to over-water — aster is very sensitive to too little or too much water and will be adversely affected by over-watering. You’ll know you over-watered if the lower leaves and stems of your aster plants are falling off after a heavy watering.

If you are growing one of the taller varieties of aster, you’ll need to hand stake each plans to they don’t collapse under their own weight.

To encourage your aster to grow in a more bushy shape, pinch off the younger growth. After they’ve bloomed for the season, cut them back in the winter to control them a bit.

Every few years you can divide your aster patch to effectively ‘reset’ them and restore their vigor and quality.​

Propagating Asters

Although you can grow aster from seed, many gardeners opt to use the division method to propagate their aster plants.

By Division​

If you already have aster plants in the garden, or know a friend who is growing them, you can simply divide their plants. By digging out over half of the aster plants and transplanting them into your own garden, you can skip the germination and seedling phases and get straight to the beautiful flowers!

From Seed

If you are growing from seed, it’s best to start the seeds indoors where you can control the environment more. You can also sow them earlier indoors.​ Lay down seedling mix into a 10×20 propagation trays, or container of your choice.  Sow 2-3 seeds in each hole, about 1/8″ deep.

Once they sprout, thin each cluster of seeds by selecting only the strongest seedling in each clump. This way you ensure the healthiest, most vigorous aster seedlings possible. After 4-6 weeks, your aster seedlings will be ready for transplanting out into the garden.

Pests That Affect Asters

Asters are quite pest resistant in general, however there is one bug that they struggle with.

Lace Bug
Lace bugs can affect aster plants.source

Lace Bug – These tiny, grayish-white bugs will show up around the middle of the summer. They prey on the underside of aster leaves and suck nutrients out of the leaves.

To identify a lace bug infestation on your asters, look for yellowing leaves. If you catch the infestation before these leaves turn brown, you can use organic sprays or insecticidal soaps to beat the bugs back. Be sure to cover the entire underside of your aster plants if you spot any lace bugs, as leaving even a few untreated will just prolong the problem.

Diseases That Affect Asters

Just as asters are resistant to most pests, they also fare well against most plant diseases…save for one of the peskiest of all: powdery mildew.

Downy vs. Powdery Mildew
The difference between downy mildew and powdery mildew. source

Powdery Mildew – ​This disease plagues gardeners around the world, whether they’re growing flowers or edible plants. The best way to prevent powdery mildew is to keep air circulation high and remove any leaves or plants that you spot the white, dusty powder on immediately as it spreads fast. Also trim your aster stems and rake around your plants to increase air circulation and remove organic matter that powdery mildew is prone to attack.

If your asters are already plagued by this annoying disease, there are many different treatments for powdery mildew. The best ones are potassium bicarbonate or food-grade hydrogen peroxide.

Final Tips for Growing Asters

Asters are a magnificent addition to any garden due to the many colors and varieties they come in. You could have a vibrant flower garden with asters alone if you wanted to! They’re low maintenance, so they make an excellent summer flower addition for beginner flower gardeners.


The Green Thumbs Behind This Article:

Kevin Espiritu
Founder

Growing asters is a great way to get started in flower gardening. Asters are very easy to grow and a beautiful addition to a summer garden!
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