15 Tips For Growing Asters in Pots or Containers

Thinking of growing asters in Pots or containers this season but aren't sure where to start? There are a few tricks you can apply to ensure you can have a container full of these beautiful flowering perennials. In this article, certified master gardener Liz Jaros walks through her top tips for growing beautiful aster flowers in pots or containers!

New England Asters

Looking to add some fall color to your patio or balcony, but not interested in spending money on annuals that die after just a couple of weeks? You might want to consider working some asters into your pots or containers.

Cheerful and charming with daisy-like dispositions and mum-like profiles, asters bloom in late summer and early fall. They are perennial flowers you don’t often think of for the container garden. But you really should. With many different aster varieties ranging in size from 1 foot to 6 feet, they come in shades of pink, purple, white, and blue.

Asters show up in the garden late in summer when everything else is dying out, and they bloom for an extended period of time. Hardy in zones 3 through 9, asters are easy to grow in a location with full sun and easy to care for throughout the season. They can work surprisingly well in containers. 

So, are you ready to learn how to grow happy asters in pots and containers? Read on for some of our top tips to help you enjoy their beautiful blooms on your balcony or patio long into the fall!

Pick The Right Pot

Choosing a Pot
Be sure to water diligently if you choose to use terra cotta pots.

When selecting a container, pay close attention to the plant’s eventual width and height. Choose a pot or container that is roughly as wide as your aster’s mature width and roughly half of its mature height. This general practice will help you achieve visual and physical balance between your aster and the vessel that houses it.

If you’re working with pots you already have in your shed, remove last year’s dirt and disinfect them with a solution of 9 parts water to 1 part bleach. New pots should also be rinsed and disinfected to prevent disease and contamination.

Think through the container material since it will likely be located in full sun. Below are some container options, as well as things to keep in mind depending on which you choose.

Clay or Terra Cotta

Clay or terra cotta pots are porous, which helps with airflow, but they also speed up evaporation. Choose clay pots only if you intend to water diligently.

Resin or Composite

Resin, cast stone, and fiberglass containers will help keep soil temperatures even, but be careful not to overwater since they will retain more moisture.

Wooden Planters

Wood planters can make for earthy, natural-looking aster containers, but they will drain quickly so you will have to stay on top of watering.

Metal Drums & Tubs

Metal drums and tubs also make great pots, but they can get very hot on warm days. Only use metal containers if they are wide enough to give roots some insulation from the container’s extreme heat.

Make Sure The Pot Can Drain

Drilling Drainage Holes
If necessary, drill holes in the bottom of your pot for proper drainage.

Asters do not like having wet feet. They are also susceptible to root rot and fungal conditions, so the container you select should have enough drainage holes to maintain even soil moisture.

When working with pots from your own shed, make sure holes are clear and that water can exit freely. Roughly ⅕ of your container’s bottom should be covered with drainage holes, and their diameters should be somewhere between ¼ and ½ inch. If you need to, use a drill to add enough holes for proper water flow.

New containers will sometimes have indications where drainage holes should be drilled, or will need to be punched out with a hammer and screwdriver.

Choose The Right Potting Medium

Proper Soil
Choose potting soil that includes both a mineral component and organic material.

To give your asters the best growing foundation, a soil-less medium should be used to fill your containers. Choose a potting soil that includes a mineral component such as vermiculite or pearlite as well as organic material like peat moss or pine bark.

You do not need to line the bottom of your pot with rocks or water bottles unless you’re short on potting soil and looking to take up a little space. If you do employ some kind of bottom filler, make sure it doesn’t impact drainage, and that it can accommodate their large fibrous root system.

Garden soil and straight compost are not recommended, as they will drain poorly and be too heavy. Also, those of you in cooler hardiness zones will likely have to relocate your pots in winter to provide some protection from extreme temperatures, and pots filled with soilless medium will be considerably easier to move around.

Choose The Right Variety

Flower Varieties
New England varieties tend to be taller, whereas the New York varieties are more compact.

With so many aster varieties to choose from, picking one to try in your container garden may seem like a daunting task. But it doesn’t have to be. Again, look for asters that are going to be in scale with your pots when they reach maturity.

Asters in the New York species are typically smaller and more compact, so you may want to select one of those for single plantings in smaller containers. A few New York cultivars to try include ‘Fellowship,’ ‘Royal Ruby,’ ‘Chatterbox,’ and ‘Audrey.’

Conversely, New England varieties can be quite tall at maturity. Use them when a more vertical display with some height is desired, and when your container is large enough to accommodate some staking or support.

Try ‘Alma Potschke,’ ‘Purple Dome,’ or ‘Barr’s Blue’ when you’d like to contain a more upright flower. Just make sure your container is also vertically shaped, with a smaller width than height.

Mix and Match

Combine Flowers
These beautiful blooms combine with other plants and flowers effortlessly.

If your container is large enough to accommodate multiple plants, consider working asters into a mix with early and mid season perennials. This will ensure that something is blooming on your patio all season long.

Look for plants that also thrive in full sun and require well drained soil. Creeping phlox and dianthus are good choices for early season interest, while catmint and salvia can be worked in to deliver some mid summer color.

Black-eyed susans or shasta daisies might be employed for mid to late summer flowers, and would overlap asters’ bloom time slightly.

To ensure that something colorful is happening in your container garden all season long, you can also pop some annuals in around your aster’s base. Consider alyssum for a spilling effect, or vinca to blanket your aster’s feet. Old stand-bys like petunias and marigolds also pair nicely with them in a container.

Don’t Overcomplicate Potting

Potting Plant
Loosely fill in soil around the base of the plant.

Planting in containers is relatively easy, and not that much different from planting them directly in the soil.

Potting Steps

  1. Remove them from their nursery container.
  2. Check for circling or compacted roots.
  3. Loosen them with your fingers or a small garden tool if necessary.
  4. Dig a hole in your container that can accommodate their root system.
  5. Insert the root ball, backfilling if necessary.
  6. This will ensure that the crown sits just above soil level.
  7. Loosely fill in around the roots, but do not compact the soil.
  8. Leave and inch or two between the lip of your container and the top of your soil.
  9. Water immediately.

Find a Sunny Spot

Sunlight Needs
For best growth, be sure your plants are getting around 6 hours of direct sunlight each day.

Position your aster containers in a sunny spot on your balcony or patio. They require 6 hours of direct sunlight for optimal health and growth. Some varieties can tolerate a bit more shade, if they have to, but full sun is ideal.

The 6 hours of sun do not have to be consecutive, but check periodically to make sure they are getting enough. Sometimes a tree branch fills in overhead or a nearby shrub has a growth spurt. If you find this happening in your yard, move them to a location with more direct light. They will flower more prolifically if you stay on top of this basic need.

Water Them Often

Watering Plant
Water around the base of the plant, trying your best to not get water on the leaves or petals.

The biggest challenge with container gardening is always irrigation. Pots dry out quickly and plants can wilt overnight. Ideally, they should be checked daily for moisture. At the very least, check them every other day. If your finger inserted into the top 2 inches of soil is dry when you pull it out, your plants could probably use a drink.

Moisten the entire root zone with a watering can or hose nozzle set on ‘shower.’ Take care not to water the leaves, as this will create the conditions for powdery mildew when temperatures are cool.

Consider adding a layer of mulch to their base if soil seems to be drying out too quickly. This will help insulate the dirt from the harsh effects of the sun.

Pinch To Shape Them

Trimming For Growth
For a more compact plant, snip the tops of your plants in early summer.

In early summer, when they are showing 3-4 sets of leaves, you may want to pinch or prune off their tops to encourage a more compact flower display. Performing this little garden trick will encourage side branching, less height, and a rounder habit that’s well suited to container growth.

To pinch your asters into a more compact form, use your fingers or a small pruning tool to snip the tops off just above the third or fourth set of leaves.

Stake Them For Height

Stake for Tall Varieties
Taller flowers may need a little extra support.

Conversely, if you’re looking for taller asters with showier flowers, you can prune off some of the side branches and their buds to encourage a more vertical habit. The result will be a leggier plant with larger blooms, but you’ll need to stake it to prevent breakage from the wind and other elements.

At the time of planting, select a cane or stake that is equal in length to your aster’s mature height and drive it firmly into the soil about 4 inches away from the root.

Regularly monitor new growth, and use garden ties or cloth strips to secure stems to the stake. Check regularly to make sure growth is not being inhibited by your ties and adjust as necessary.

Deadhead Them Often

Deadhead Spent Blooms
Remove spent, withered blooms to encourage new growth.

Faded blooms should be removed promptly to prevent them from going to seed. Since dying flower heads are an indication that seed production has begun, a flower’s growing system will then divert its focus from creating showy blooms to nurturing its roots and foliage.

When we remove spent or fading flowers from a healthy plant, we are actually tricking the plant into thinking it should send up more blooms.

To properly deadhead, use your pinched fingers or a small pruning tool to snip off spent blooms just above a set of leaves. Get in the habit of doing this every few days during their bloom cycle, and you’ll get more vigorous blooms for a longer period of time.

Fertilize Them Sparingly

Proper Fertilizing
Fertilization is not required if using a potting mix that contains slow release fertilizer.

Most likely, your potting mix was amended with slow release fertilizer and they should not require an additional supplement until later in the season. Check the label to see what kind of feeding you can expect from your medium. A nitrogen rich fertilizer aims to create strong stems and leaves, while a phosphorous/potassium rich fertilizer is directed at blooms.

In mid summer, when blooms are beginning to form on your asters’ stems, a water soluble fertilizer can be applied to encourage a bigger, better flower cycle. But this should only be done once, and never when there is drought or plant stress.

Organic plant food such as bone or fish meal can be applied more often as it will not hurt the plant. You may experience a slightly less productive flowering period, but they are pretty showy to begin with. You probably won’t even notice the difference and you’ll be cultivating a natural garden.

Cut Them Back Regularly

Cut For Winter
Wait until your plants have been killed off by several frosts before cutting back your plants.

Since asters hold no real winter interest in the landscape, they should be cut back to just above soil level when their blooming is complete. Doing so prevents the spread of diseases like powdery mildew and makes overwintering your pots a little easier.

Steps For Cutting Back

  1. Wait until several frosts have killed off the flower tops.
  2. You’ll see the stems and foliage are brown.
  3. Make your cut about 2 inches above soil level.
  4. Use bypass pruners or a small shears to make cuts.
  5. Compost your the tops if they’re healthy.
  6. Dispose of them if they’re showing insect of fungal issues.

Divide Every Few Years

Divide Plants
If you notice your plants are becoming crowded, divide and replant them.

When they begin to show signs of crowding, you’ll need to divide and replant them. This will prolong the life of your original aster and give you several more to locate elsewhere in the garden!

How to Divide

  1. In early spring or late fall, dig out your plant.
  2. Lay them on a tarp or piece of cardboard.
  3. Use a clean, sharp knife to slice your aster’s rootball into multiple sections.
  4. Take care to leave a couple of shoots and some root tissue in each clump.
  5. Replant all sections immediately.
  6. Water immediately.

Protect Them in Winter

Winter Care
Add a thick layer of mulch in your pots to protect your plants from cold winter temperatures.

While asters are perennial and hardy down to zone 3, they may require a little extra protection in regions that receive excessively cold temperatures. Once cutbacks are made, you may want to cover the dirt with a thick layer of organic mulch.

You may even want to pile mulch up around your pots’ sides, especially if they are smaller and less insulated. It can also be helpful to group perennial pots together in a sheltered area that’s away from high winds.

Final Thoughts

Asters bloom well into the fall, long after most perennials and many annuals have stopped doing their thing. When planted in containers, they can be moved around and worked into an autumnal arrangement of pumpkins, pansies, and scarecrows, or left alone to show off their masses of colorful blooms.

When the season is officially ended and you’ve put them to bed for the winter, it’s nice to know they’ll be coming back next year. Hopefully bigger and better than ever.

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