How to Grow and Care for Chrysanthemums

Chrysanthemums (Chrysanthemum morifolium) are symbols of fall, with domes of vibrant, jewel-tone colors. To tempt gardeners to purchase these late-season bloomers, they are often sold in full bloom. That is fine if all you want is an instant seasonal decoration, but not good if you are hoping for a hardy perennial plant. Plant them in the spring to give them plenty of time to take root so they will bloom for many years.

You can always grow mums as annuals. They do provide wonderful fall colors and work great at filling in empty spots where summer bloomers have faded, especially considering they can quickly reach up to 3 feet in height. Look for plants with lots of unopened buds to have blooms well into the fall season.

If you have dogs, cats, or horses, be aware that chrysanthemums are toxic to pets.

Chrysanthemum Care

For mums to be truly hardy, they need time to become established in the ground. Ideally, they are best planted in the spring and allowed to grow in place all season. Unfortunately, the mums for sale in garden centers in the fall have been coddled in nurseries and coaxed to set buds for September blooms. That means they are putting an awful lot of energy into blooming, not growing roots.

Planting these specimens in the garden in late summer or early fall does not guarantee sufficient time for the plants to become established. This is not a problem in warmer climates, where a bit of deadheading will satisfy most mums after bloom, but in areas with sub-zero winters, perennial plants need strong roots to anchor them into the ground. The repeated freezing and thawing of the soil will heave the plant out of the ground and kill the roots.

Spring-planted mums will have plenty of time for root growth. Many gardeners are surprised that their garden mums start to bloom in mid to late summer. If you want fall flowers on your mums, you will need to pinch the plants back periodically throughout the summer. Start when the plants are about 4 to 5 inches tall and repeat every two to three weeks until July 4. This will cause the plant to get stocky and bushier, and by late summer, it should be covered with flower buds.

Light

Although mums can handle partial shade, you will get the fullest plants and the best blooms in full sun. Try to plant mums where they will receive at least six hours of sun a day.

Soil

All mums prefer fertile, well-drained soil, with lots of organic matter or compost worked in. They like a soil pH slightly on the acidic side.

Water

Mums prefer evenly moist soil. Water the plant when the top 1 inch of soil feels dry. If watering in a pot, water the soil surface using a watering can until moisture begins to drain from the bottom of the pot. Check your pots for drainage holes before committing to using them. Water should drain freely through the soil and out the bottom of the pot when watering. Soil should remain moist, but not soggy. Soggy soil can cause root rot and other diseases.

Temperature and Humidity

As their nickname, "hardy mums," suggests, they can handle cool temperatures. Mums can overwinter in the ground, and they do so even better in warmer climates.

In warmer climates, consider the effects of heat delay on your mums. If you have high temperatures, particularly at nighttime, it can cause the plant to flower later than it usually would. Heat delay can cause irregularly formed flower buds, erratic flowering, deformation of the plant’s crown, and other developmental issues. To bypass this problem in hotter climates, look for cultivars with higher heat tolerance.

Fertilizer

It is crucial to feed chrysanthemums during their vegetative phase. Use a 20-10-20 fertilizer when planting and during the vegetative growth period. Superphosphate helps aid root development. Once established, switch to a 5-10-5 liquid fertilizer. The general rule of thumb is to begin after all danger of frost has passed. That way any new growth forced by the nutrients will not be in danger of damage from icy weather. Established plants should not be fed after July, so new growth is not injured by frost. For amounts to use, follow product label instructions.

Types of Chrysanthemums

There are multiple mum varieties available based on the desired flower color, bloom time, and petal shape.

• ‘Ruby Mound’ features early-season bloom with large, maroon-red flowers.
• ‘Patriot’ offers mid- to late-season bloom with pure white pompom-shaped flowers.
• 'Tripoli’ features very-late-season blooms with daisy-like flowers of vibrant pink with yellow centers.

Propagating Chrysanthemums

You can propagate mums by division and cuttings. The most straightforward and fastest method is division. Here's how to propagate mums.

To divide by root division:

Divide plants that have grown in the garden for at least two years. Younger plants will not have a sufficient root system to survive.

1. By every third spring, divide chrysanthemums to rejuvenate them. Do this in the spring.
2. Pick plants that are at least 6 inches tall.
3. Dig a clump of mums out of the dirt, shake away the dirt from the roots, and then begin to divide the plant in two (or three depending on the size of the clump) by carefully untangling its roots without damaging them.
4. Replant them at the same depth as the original plant, spacing them at least 18 inches apart for good air circulation.

To propagate from cuttings:

This is an excellent method to get a replica of the plant you have. It eliminates the mystery of what the plant will look like, which is often the case when planting from seeds. There are extra steps to propagating from cuttings.

1. Cut a stem that is at least 4 inches.
2. Pinch off the lower leaves.
3. Dip the cut end into a rooting hormone.
4. Plant the cutting in a container. Keep the container in a warm spot in the house, ideally in an area that has indirect bright light.
5. Keep the soil slightly moist. Wait about four weeks or so for a root to grow.
6. Let the plant grow another 2 inches, then transplant it outside.

How to Grow Chrysanthemums From Seed

Mums can grow from seeds, but it is best if you use purchased seeds. If you attempt to plant seeds from your own plants (most are hybrids), the resulting plant may not be true to the parent. If you are okay with surprises, then go for it. Start seed indoors, following seed packet instructions, six to eight weeks before your last frost date. Harden off plants before transplanting outdoors.

Potting and Repotting Chrysanthemums

Repotting is the single most important thing you can do to increase the longevity of your mums. Most mums are completely root-bound when you get them. The roots have usually taken up the entire pot, which makes it difficult for the soil to retain any water.

To repot, choose a container of any material (from plastic to clay) that is a little bigger than the last container. Make sure the pot has drainage holes. Fill the bottom of the new pot with good-quality potting soil. Gently break up any roots you can, but do not damage the roots.

When you put the plant in the new pot, the surface of the soil should be an inch below the lip of the new pot. Make sure you have soil, not air surrounding the roots. Tamp down the soil gently. Give the pot a good watering until it flows out of the bottom of the pot.

Overwintering

Overwintering mums is more of a concern for chilly regions. For fall-planted mums to have a better chance of survival in cold areas, you need to give the roots and crown of the plant extra protection. First, leave the foliage on the plants until spring. Do not prune them back after frost has turned them brown. Then, either mulch the plants heavily with at least 4 to 6 inches of mulch or dig up and plant in a pot and move the plants to a more protected spot in the garden for the winter. If you choose to move the plants, do so before the first hard freeze.

Common Pests & Plant Diseases

Many pests and diseases can attack mums, but they usually don't, which keeps the plants hassle-free. However, be on the lookout for the common aphid, spider mite, and leafminer.

The long list of diseases that can damage mums includes viruses like smut and mosaic. Various fungi, like leaf spots, rust, wilt, powdery mildew, gray mold, and blights can infect chrysanthemums. Mums are also vulnerable to the bacterial disease, crown gall.

How to Get Chrysanthemums to Bloom

To get a full mop of those soft and tightly mounded daisy-like petals blooming throughout its fall season, it helps to purchase a potted plant with an endless amount of unopened buds, repot it, and keep it in full sun. Without a little more consistent maintenance, however, your mum's blooms will only last a couple of weeks. There are simple ways to encourage more blooms from August throughout October, whether your mums are in pots or the ground.

Pinch growing mums throughout the spring and in summer until around the fourth of July to encourage branching and development of more buds. Keep watering your mums but don't drown the roots. These are very thirsty plants that need moisture to keep up their energy for flowering. Add water below the blooms to avoid damaging them. Also try to consistently deadhead your mums when you see spent or nearly-spent blooms, which helps the plant put its energy into producing new flowers.

Common Problems With Chrysanthemums

As hardy and easygoing as they are, mums can develop a few problems in the ground or in pots as a result of watering problems, pests, or diseases. Here's how to spot and correct issues.

Decaying Leaves

If you find the leaves on your mums are becoming yellow, then turn black, and finally drop, the plants have likely been overwatered. Leafminers could also cause dried, drooping leaves, which will need to be pruned and destroyed.

Spotted Leaves

Spotted leaves on mums have many causes. Fungi can cause spots (from yellow to orange to darker colors) on leaves. Handpick infected leaves and use fungicides to stop the spread. Yellow spots on leaves could be the work of spider mites so look for their fine webs that can be removed with insecticidal soap or water sprays.

Stunted Growth

When mums do not grow, or they are leggy and woody, it usually means the plants were not watered enough and are exhibiting signs of drought. Also check for pests, such as aphids, which tend to distort the growth of mums, but can be easily removed by hand or water sprays. Wilt, a fungus, causes plants to become stunted and flowerless, so infected plants should be removed to prevent spread.