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

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, and 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 aster’s crown 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, wash the roots in clean water.

You can then use a clean tool to trim away roots that look affected. 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 a 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.

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.

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 aster’s 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 be ready to remove any new growth that shows signs of fungus.

Keeping in mind that fungal diseases occur mostly above ground, a plant 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 that’s transferred most often by leafhopper insects. Cultural pest control will be crucial to preventing future outbreaks (see below).

As for mitigating the damage right now, a plant that’s suspected 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 bateria 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 promptly.

Insect Problems

Chrysanthemum lace bugs are the insect most likely to cause major damage to asters. 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 sidestem.

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

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 blooms 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 something is wrong 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.