How to Grow Large Chrysanthemum Blooms

 

2023 update: We hope you'll join us for A Festival of Fabulous Mums on Nov. 4 & 5 from 10 a.m. to 4 p.m. Admission to this indoor & outdoor festival is free. A flower show competition sponsored by the Central Carolina Chrysanthemum Society and the Raleigh Garden Club will feature the skill and creativity of mum growers and floral designers from near and far.  We're also offering a guided tour of our outdoor mum displays led by Duke Gardens horticulturist and award-winning mum grower Michelle Rawlins on Oct. 31 at 1:30 p.m. Read more & register for the tours on our programs website. Parking fees apply ($2/hr.).

 

By Michelle Rawlins
Horticulturist, William L. Culberson Asiatic Arboretum

Chrysanthemums are often viewed as an old-fashioned plant and frequently ignored. Since we have started growing them at Duke Gardens and exhibiting them throughout the William L. Culberson Asiatic Arboretum, they have become more popular and noticed by many visitors.

Garden enthusiasts and novice growers often wonder if they would be able to grow something similar at their home. Indeed, many home gardeners have been growing large flowering chrysanthemums in their gardens for years. Below are instructions for growing a chrysanthemum of your own in a container, based on our experience here at the Gardens. For more detailed tutorials, please visit the National Chrysanthemum Society’s website.

January & February

This is the crucial time to plan for the entire season of mum growing. It comes at an ideal time, since most of the garden is in its rest period.

The first step is to research mum cultivars and select a few that spark your interest. Keep in mind that chrysanthemums vary in size, color, height and bloom time. You can view all cultivars available in the United States through King’s Mums, the only grower currently offering them for sale. This nursery grows and sells on a first come, first served basis, and the buying season closes in early spring. Another option is to join or become friends with someone who is a member of the Central Carolina Chrysanthemum Society, which is based in Raleigh. The members of this club love to share cuttings and encourage others to plant chrysanthemums in their landscapes.

This is also a good time to gather other essential supplies. You’ll need some containers, starting with 3-inch plastic pots, and including 1-gallon and 3-gallon pots to provide enough room for root growth and development. For a potting mix, you’ll want one that drains well. We use a brand called Jolly Gardener Pro-Line growing mix, but we also add aged pine bark at a 50/50 rate to add even sharper drainage.

Once you have your plants, they must be watered daily, and the correct fertilizer is key for healthy growth. During the growing season, we fertilize with Miracle Gro water soluble fertilizer with a 24-8-16 analysis. It is high in nitrogen and will keep your foliage looking lush and green. When the plants start showing tiny buds, we switch to Miracle Gro bloom booster flower food with an analysis of 15-30-15. This will continue to feed the foliage, but its higher phosphorus content will provide lots of food for flower power.

Lastly, you will need to find 4- to 5-foot bamboo canes and twist ties to use for stem support during the growing season. The flower heads have quite a bit of weight to them, and if they are not properly supported, they will be lying on the ground at the end of the season.

March — May

For gardeners who have access to stock plants and prefer to start their own plants rather than purchasing them, spring is the time to take cuttings. We take hundreds each year for the arboretum from stock plants that have overwintered in our greenhouse and nursery area. These plants respond to spring warmth and longer days by producing healthy new shoots, which are easily rooted in a moist medium out of direct light. We start 6- to 8-inch cuttings on our propagation mist benches in the greenhouse, but cuttings can be successfully rooted at home as well. The most important thing is to always keep a label with each cutting, or else you won’t know which plant is which.

If the temperatures are warm and there is plenty of sunlight, cuttings will develop enough roots to be potted up  into 3-inch containers. Once the cuttings are transplanted, you can also add some slow-release Osmocote fertilizer to each pot.

Make sure the plants dry out before you water them again, because root growth is most important during this stage. If plants stay too wet, they will not send out roots to search for water. If plants reach over a foot in height, pinch them back to 6 inches to encourage branching.

June & July

As temperatures increase and days lengthen, the plants will really be growing well now.  It is very important to keep your plants in an area of your yard that gets a minimum of six hours of full sunlight, with morning light being the best option. They should be transferred to 1-gallon pots in May or early June, and finally to their 3-gallon final pots by early July. However, these are just guidelines; you should only transplant when their roots have completely filled the pot, but before they become root-bound.

When the plants are in 1-gallon pots, we feed them every 10 days with water soluble Miracle Gro fertilizer. After they are in their 3-gallon pots, we feed them every 7 to 10 days. In the first week of July, we cut all of the foliage back to 6 to 8 inches. This will ensure that plants will not be too tall and top-heavy when they develop their buds and start flowering in the fall.

In late July, after plants have recuperated and branched from that hard pruning, choose three to five stems to grow to their full potential in the pot, and remove all other stems and growth. From here on, your goal is to foster the growth of the trained stems, and to remove all other growth for the remainder of the season. Use your bamboo stakes as the support system for the stems that you choose to train. Tie the stem to the stake every 8 inches or so while the plant grows, rotating the pot every week so the plant grows straight.

August & September

Chrysanthemums love warm weather and full sun, and they thrive in the hottest part of summer. The biggest challenge this month will be to keep up with removing lateral growth on your plants. If you look along your trained stems, a lateral stem will form everywhere there is a leaf, emerging from the same point. It is important to remove all these lateral stems, and to do so when they are young and soft. Trying to remove them after they have aged will be much harder and leave more prominent scars along the stem.

Keep up with fertilizing during the summer months, and keep an eye on pests. Chrysanthemums are aphid magnets, so remove them with a jet spray of water, or by hand if you are going for a pesticide-free plant. You may also want to try an insecticidal soap. Caterpillars can also be removed by hand before they damage the foliage. We try very hard to remain pesticide-free here at Duke Gardens, since chrysanthemums are pollinator plants that attract several different species of insects.

Mums will start to display flower buds now as they sense the shortening days, though the exact timing will depend on whether the variety is an early, mid-season or late bloomer. You can manipulate your mums into blooming earlier by shading them, but that is a more advanced technique outside the scope of this article. Once a bud forms, it typically takes another full month to see color and for the flower to start opening. Make sure to keep those pesky aphids off the buds, because they can damage the petals.

Make sure there is only one terminal bud at the top of each stem. If you see several buds, carefully remove all other buds growing alongside the big bud at the very top. This will ensure that the largest flower will develop at the end of each stem that you have trained. Make sure the last twist tie is just below the head of the flower for added support. The stake can be cut just below the developing bud so it will not interfere with flower development.

October — December

This is truly the best time of year! The days get shorter and the nights cooler. Trees will start showing color, and what more fantastic plant to grow alongside them than a fall-blooming mum? The mums will start by showing color and then unfurl hundreds of colorful petals until they fully expand into a large flowering chrysanthemum.

Keep the plant well-watered during this time, as any stress will cause premature aging and the bloom will wilt that much faster. It’s also important to protect plants from excessive rain from fall storms and hurricanes. If a significant amount of water stays on the bloom, it will rot. To remove excess water, simply hold the bloom by its neck and give the stem a quick shake.

Share blooms with your friends, family and neighbors. Remember to take notes and photographs of your favorites to grow again next year, as well as which ones you were not impressed with, or with which you had a failure of some kind.

Once plants have finished blooming and look tired, you can cut them back to 6 inches once again and find a nice dry spot to overwinter them. Try to keep them from freezing and thawing repeatedly, to ensure that the plant will survive the winter ahead. Some people overwinter them in a garage, where they can water them periodically and they’ll get a little bit of sunlight.

We hope you enjoy growing chrysanthemums in your garden and have lots of success with the aid of these instructions. For more information, please visit the National Chrysanthemum Society’s website, or contact me directly at michelle.rawlins@duke.edu.

Photos from top: 'Fleur de Lis' chrysanthemum in the Culberson Asiatic Arboretum, by William Hanley; cuttings in the greenhouse, by Michelle Rawlins; detail of the emerging roots of a chrysanthemum cutting, by Michelle Rawlins; pinching back unwanted growth on a chrysanthemum stem, by Michelle Rawlins; detail of lateral buds emerging from leaf shoots, by Michelle Rawlins; detail of a terminal flower bud, by Michelle Rawlins; 'Gerturde' chrysanthemum on display in the Culberson Asiatic Arboretum, by William Hanley.