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Chrysanthemums, more commonly referred to as “Mums” are delightful late bloomers suited to indoors or out in the garden. Annuals can barely survive without specific care instructions. When even the hardiest varieties of Mums are dying, gardeners can be left confused as to the reason why.
Fact is, a number of factors can lead to the early demise of Mums, both in pots, and in the garden. Outdoor hardy Mums are more difficult to keep alive over the winter.
Container grown Mums, you may expect to be easier to grow, but surprisingly, that is not the case. The plants need to be repotted in a suitable container, and with appropriate soil to stand a chance at surviving.
8 Common Reasons for Mums Dying
1 – Immature Rooting System
All types of potted Chrysanthemums become root bound fast. Hardy Mums only survive winter when they have a strong root system. They can only get that when they are planted in early spring to benefit from full sun in the summer.
Buying a potted Mum near fall season to plant in the garden is likely to see it die when the first frost hits. The roots will not be strong enough to support it over the winter.
How you care for Chrysanthemums depends on when you buy them and how you intend to grow them. In the spring, garden perennial varieties of Mums can be planted outdoors.
Later into the summer months, even hardy Mums will be too late for the garden. They can be potted and overwintered indoors, then planted outdoors in the spring of next year.
When working with potted Mums, it is beneficial to know that you are caring for a hardy variety that can cope outdoors. If what you have is an annual variety, often purchased after the spring, those are difficult to keep alive beyond a single season.
The reason is that annual Mums are forced to bloom. They look great in garden centers and nurseries, enticing customers to buy them. The root system will rarely be strong enough to survive more than one season.
In the first year, the challenge with annuals is just keeping them alive by nourishing the rooting system while providing adequate growing conditions that doesn’t force the plant to bloom too early. The trick to longevity is to control where the plant exerts the most energy and when.
When they are immature, the best thing you can do is focus on caring for the root system. Worry about blooming once it has the resources to continually re-bloom.
2 – Lack of Mulch
Hardy Mums can last for years in the garden provided they are in an area that receives plenty of sunlight and aren’t ignored during the growing season.
The one thing that no Mums are is cold-hardy. Perennials are hardy to an extent, but there will always be parts of the plant die off in the winter.
The extent of the damage that happens over the winter will depend on the level of protection in place. The best protection is a deep layer of mulch. The alternative is to accept that the plant won’t survive the frost and cut it back to near ground level before the frost hits.
Whether you cut Mums back before frost, or bulk up the base with mulch is a matter of preference. Doing nothing will all but guarantee the death of a garden mum plant.
3 – Adverse Weather Leads to Overwatering
Very few plants fare well with too much water. For garden varieties of Chrysanthemums, heavy rainfall will result in Mums turning brown. In most cases, when that happens, the mushy parts of the plant will need to be removed.
Given that these are late bloomers, if you are in a region that frequently gets heavy downpours, it may be worth investing in plastic tarps to shelter any fragile plants in your garden when the forecast is for heavy rainfall, sleet, or hail.
In most instances, Mums out in the open with no protection wind up drowning from too much rainwater. The vast majority of the damage is to the buds, and foliage. At the soil level, mulch can serve as a partial barrier to protect the root system.
Unfortunately, for any late bloomer plant in the garden, when adverse weather hits, there are parts of the plant that won’t survive. The more they can be sheltered, the easier it will be to nurse them over the winter.
4 – Potted Mums Are More at Risk of Root Rot
When any plant receives too much water, it risks rotting the rooting system. Root rot is not limited to just drowning the roots, starving them of oxygen. The biggest concern is fungal and bacteria diseases that latch onto overly moist parts of the plant.
Potted mums are more susceptible to root rot. This is because they are full sun plants that do not fare well in shade. Being full sun plants, the soil dries (or should dry) faster, requiring more frequent watering.
Novice gardeners tend to wonder why their Mums are wilting, discover that it is because of a lack of water, so they go and add some more. That can be the case, but more often than not, it is the soil that isn’t optimal for the plant.
In most instances, potted Mums need to be repotted in a suitable container and with more appropriate soil than what the stores supply the plant. This is usually a highly fertilized soil specifically enriched to force Mums to bloom.
What you really need is a super-fast draining soil.
Almost always, newly purchased Mums are root bound when you buy them. The best thing you can do with a new Mum is to repot in a better soil for faster drainage, and in a pot 2-inches bigger than the one the plant is in when you buy it. That ensures the roots have room to grow.
The room to grow carries over to Mums in garden beds too…
5 – Overcrowding
For Mums to survive, they need sufficient root growth. As previously mentioned, repotting in a bigger container will fix that. But what if you’re planting multiple blooming plants in a garden bed? That becomes another issue.
With so many varieties of Chrysanthemums, you could plant an entire garden bed of Mums. If you do, each is best to have at least 18-inches between them to allow room for the roots to become established.
Overcrowding a garden bed can lead to the roots fighting for survival. When roots of plants have to compete for nutrients in the soil, the usual result is none of them win. Instead, all the plants in the garden bed do not grow as best as they could do if they were given adequate room.
A small sacrifice of space in garden beds in the first year will result in more profuse flowering in the later years when the root zones become established.
Fungal Diseases that Can Kill Chrysanthemums
6 – Verticillium Wilt
Verticillium is soil-borne fungus infection that is difficult to treat. The wilting differs from what you would expect of a thirsty plant. Accompanying the drooping leaves will be yellow veins.
The yellowing of the veins is the Verticillium fungal pathogen spreading from the roots up through the plant. The farther it spreads, the less effective nutrients can be delivered.
The result is that the plant cannot get the nutrients it needs from the soil. The most troublesome part of dealing with Verticillium wilt its high resistance to fungicides.
Treating Verticillium wilt of chrysanthemum plants is near impossible. The most reliable method to help some of the plant survive is to take a disease-free cutting and plant in sterilized soil – soil that has been heated to 160oF for a minimum of 30-minutes.
Effectively, once the fungus is in the plant, it will die. A healthy part of the plant needs to be removed then potted, similar to how you would divide established Mums, only this time, in sterile potting soil.
7 – Septoria Leaf Spot
Septoria is a fungal disease that causes dark leaf spots to appear, sometimes with a yellow halo surrounding the spot. Septoria infections start at the lower most leaves then spread upwards.
This disease slowly kills the plants by cutting off its ability to photosynthesize efficiently. It is spread by water, either by directly watering the leaves, or by rainfall causing the pathogens to splash to nearby foliage.
The size of the spots differs, but they can cover up to a third of an infected leaf, at which point the leaf dies. The more leaves that become infected, the more of the plant that will die. The longer that goes on, the less chance there is of any healthy leaves surviving.
The only way to stop the spread of Septoria is a weekly fungicide treatment. Additionally, all infected leaves would be better cut off and disposed of rather than waiting until the leaves drop as the fungal pathogens can overwinter in soil, essentially lying in wait to strike again next season.
8 – Pythium Root Rot and Stem Rot
Pythium is one of the more prevalent types of root rot to infect Chrysanthemums. It is considered a plant parasite rather than a fungus. It is a water mold that absorbs nutrients. When it latches onto the root systems of plants, the mold grows instead of the plant. The result is a form of root rot and stem rot.
Pythium rot starts at the base of a stem and spreads upwards. Growth of the plant will be stunted; the leaves will discolor and the plant will eventually die if it isn’t treated with a suitable fungicide that specifically targets the Pythium parasite.
When this gets a foothold, it would be best to prune away diseased parts of the plant, then replant a healthy cutting.