8 Common Reasons Your Asters Are Dying and How to Fix it

With summer on the wane and most of the flowers beginning to show their age, at least you’ve still got asters to look forward to. With their full-bodied autumnal display expected from August to October in zones 3-8, asters can usually be counted on to give you one last perennial pop in the yard before winter creeps in.

Cultivated in colors of pink, purple, blue, white, and yellow, asters range in height from the shrubby, 10-inch tall ‘Chatterbox’ to the leggy, 6-foot tall ‘Harrington’s Pink’ and come in all sizes in between.

Daisy-like in appearance, asters greet fall in the company of black-eyed susans, sedum, and Joe-pye weed. They bloom prolifically for up to 4 weeks and pour on the cottage charm right when we need it most.

But what if they don’t? What if something has gone terribly, horribly wrong and your asters look like they’re at death’s door? Although asters are known for being relatively easy to grow, there are plenty of potential reasons they may start to suddenly die off. Let’s look at 8 common reasons your asters may be dying and discuss ways to prevent or address each issue.

Root Rot

If asters are planted in a bed or pot with poor drainage, or if they’ve been on the receiving end of excessive irrigation, they may be suffering from root rot. Asters require even, well-drained soil for healthy growth. Soggy roots are a major threat to their longevity.

Look for plants with stunted growth and yellow leaves to indicate the possible presence of root rot. Your dying asters’ crowns may be sunken and brown, with thin, stringy roots and limited root hairs. Leaves may wilt and stems may crack or peel easily.

The Fix

Once you see the full effects of root rot in your aster beds, it is likely too late to reverse the course. Plants should be dug up, along with the soil that surrounds their roots, and disposed of.

You may be in luck if you catch root rot in its early stages. Perhaps flooding conditions or something unusual has put you on high alert for the condition. If so, you can dig your asters up and wash the roots in clean water.

You can then use a clean tool to trim away roots to revive your dying asters. Ensure that soil is well drained going forward, and replant.

As for prevention in the future, the best way to avoid root rot is by planting asters in loamy or humus-rich soil. Regardless if you plant asters in containers or in the ground, this should help discourage occurrences of standing water.

Drought

Conversely, asters may suffer when conditions are dry and they are not getting enough water. While they are known as low maintenance and relatively drought tolerant, your aster’s transpiration process may force it to shut down in an effort to retain moisture.

This process involves absorbing water through the roots and releasing it through pores in the leaves. When this happens, leaves will turn yellow-brown and dry out. They may appear scorched or brittle and might roll under. Flowers may sag, wilt, or drop petals, leading to your asters dying.

The Fix

The goal with asters is to provide even watering and a healthy soil mix. It should contain organic content and leans toward loamy.

Consider working some humus into the soil around your asters. Make sure they are getting at least an inch of supplemental water a week during dry periods. Do not fertilize in times of stress, and consider adding a layer of mulch to encourage moisture retention.

If you want to avoid this problem altogether, choose species native to your region. These are well-adapted to weather extremes.

Fungal Disease

Above ground, asters are susceptible to fungal conditions, especially in regions or periods of high humidity. Powdery mildew is perhaps the aster’s biggest fungal foe and will present with a white, powdery coating or spots on leaves. Heavily infected leaves will turn brown and shrivel.

Botrytis blight is another fungal condition that affects asters. You will likely notice this condition first on flowers, as they will turn a spotted, papery brown color or may even fail to open. Tan to brown, target-shaped patterns may also appear on your dying asters’ leaves.

The Fix

While fungal disease is unsightly and can look like death is imminent, it is not necessarily fatal. If caught early, prune off affected leaves and/or blooms and dispose of them in the garbage.

Keep your garden beds tidy. Then space them generously to provide plenty of airflow. You’ll also need to remove any new growth that shows signs of fungus.

Keeping in mind that fungal diseases occur mostly above ground, a dying aster that is too far gone with either powdery mildew or botrytis blight can be cut down to soil level and disposed of. Next year’s growth will likely be fine. But you’ll need to keep your eyes peeled for early signs of fungal disease. Fungal diseases can overwinter in the soil.

Bacterial Disease

Aster yellows are the most common bacterial threat. The presence of yellows disease may be indicated by slow or stunted plant growth with discolored pale green to yellow-white leaves. Stems typically form close together or fan out in a witch’s broom pattern. Flower buds may be small, malformed, or discolored.

The Fix

Aster yellows is a persistent bacteria transferred most often by leafhopper insects. Cultural pest control will be crucial to preventing future outbreaks (see below).

As for mitigating the damage, dying asters of being infected with aster yellows should be dug up and removed. The condition is almost always fatal and will spread easily to nearby plants.

Since the disease can overwinter in the dirt and weeds, remove as much of the surrounding soil as possible and stay on top of weeding. Monitor plants in the affected beds closely next year for signs of contagion and address them promptly.

Insect Problems

Chrysanthemum lace bugs are the insect most likely to lead to asters dying. They feed primarily on the undersides of leaves where they use piercing/sucking mouthparts to draw sap from leaves. Lace bugs are indicated by a stippling, bleached pattern when you flip your asters’ leaves over.

Spider mites and leaf hoppers will destroy aster leaves in a similar manner to lace bugs. However, they will not leave raised black specs (excrement) in their wake.

The Fix

Generally, insects themselves are not likely to kill your asters unless the infestation is severe and unchecked. But the stunted growth, leaf drop, and poor overall appearance may make you think that’s what’s happening. And as mentioned, leafhoppers and many other insects can also spread disease.

Removing affected plant parts or cutting them down can help slow the spread of insects. Neem oil applied in the early morning on dry days will definitely help reduce populations.

Fallen leaves and petals should be removed from the garden promptly to reduce habitat options. Some luck may also be had with the introduction of reflective elements that will disorient pests.

Pesticides are not recommended, as they are likely to throw off the predator/prey relationship and introduce even bigger problems to your garden.

Lack of Deadheading

Just because your asters’ flower heads are dried up and brown, it doesn’t mean the whole plant is dead. Newbie gardeners often think something has gone wrong when brown blooms start to cover their asters, but it’s just part of their natural cycle.

As long as stem tissue is green, dead flower heads are an indication to a plant that reproduction has occurred successfully, and flower production is complete for the season. Plants will then stop sending up blooms and direct nutrients toward their root systems.

The Fix

Make it a point to buzz through your aster patch every few days to remove blooms that are on their way out. Beginning just beneath the base of a spent flower, slide your fingers down its stem until you reach either a set of leaves, a new bud, or a side stem.

Make your cut just above one of these points and you won’t be left with unsightly, headless stems that make you think your asters are dying. In just a few days, they will reward you with new growth from the nodes just below these regions. Ultimately, new flowers will form.

You can also leave seed heads on your aster plants to feed foraging birds in winter.

They Need Division

If your asters have sparse bottom foliage, have trouble staying upright, and seem to be flopping over in a circular pattern, leaving a dead hole in the center, they probably need to be divided. Limited flower production and smaller bloom sizes are also an indication that deadheading is required.

Since aster roots spread outward from a central clump, the inner section of a plant does not benefit from rejuvenating root growth and may appear ‘dead.’ But all asters really need is to be separated and transplanted.

The Fix

Divide your aster every 2-3 years in early spring, before new growth has begun. Dig down around its root ball, giving roots plenty of clearance, and lift the entire plant from the ground. Lay it on its side on a tarp or in the grass.

Using a sharp knife or a flat-edged shovel, make a clean cut through the root ball to create three or four separate plants. Cut away and discard the aster’s center-most roots. Replant each section as an individual plant and suddenly you’re propagating asters!

They’re Entering Dormancy

Since asters bloom long into fall, it can be hard to tell if your asters are dying or if it’s just time for them to get ready for winter. Generally speaking, if it’s late in the season and there’s a chill in the air, browning aster plants are an indication that dormancy has begun.

The Fix

While you can’t prevent them from entering dormancy, there are a few things you can do to ensure that they get healthy rest.

Some gardeners choose to leave the dried flowers in place for winter interest and wildlife food supply, while some prefer a tidier end to the season. Either way is fine, just be sure to cut in late fall or early spring, when they are not actively growing.

Asters should be cut down to about 2 inches above soil level, leaving a basal rosette of leaves just above the ground. A thick layer of mulch can be applied to help insulate them from extreme temperatures.

Key Takeaways

If you find yourself face to face with dying asters, you are likely witnessing the effects of improper watering, disease, insects, or natural behavior. Take a few minutes to examine their leaves and stems to see if it might be something fungal or bacterial.

Check the quantity and quality of blooms to see if you might have a maintenance issue. And take measures to discourage insects and encourage airflow. When properly planted and cared for, your asters will deliver autumn joy for years to come.