Culture Guide for Garden “Hardy” Mums

Monday, June 14, 2021
Garden mums are a popular and relatively easy crop to grow. If grown outdoors, where they do their best, all they ask for is food, water,  light, and a bit of supervision.
Garden mums are a popular and relatively easy crop to grow. If grown outdoors, where they do their best, all they ask for is food, water,  light, and a bit of supervision.

Regardless of when mums are planted, all will initiate flowers with the shortening of days in late July. Garden mums are short-day plants that will grow vegetatively during the longest days of summer and initiate flower buds with the shortening of days, around July 20 here in the Midwest.

If you want larger plants, you’ll need to schedule your plants to arrive earlier and if you’re happy with smaller plants, it is best to schedule them to arrive later. All will initiate buds around the same time,  regardless of when planted. The most popular ship weeks for rooted cuttings are in late May and early June.

Mums are divided into early, mid-season, late, and season-extender varieties. Each has an approximate flowering date and most mum providers will list this for you.

Early – late August to early September
Mid – mid to late September
Late – late September to early October
Season Extender – mid-October

The above timing is when flowers are just one-quarter open. This can fluctuate a bit depending on summer temperatures and other environmental/cultivation factors that may vary from year to year.
Image Credit: Amy Hempen, Columbia Public Schools

Upon Arrival:
Please plant cuttings as soon as possible. If you are not ready with larger pots when your mums arrive,  you can plant them into smaller containers to be bumped up later. Try to plant within a few days of receiving cuttings.

Make sure cuttings stay watered and in bright light until planted.

If cuttings are not planted soon after receiving, they can begin to harden off and lose their ability to branch and grow as they should. You can fertilize before planting to keep them in an active growing state.

Use a porous soil mix with bark or coarse peat moss when growing mums outside. Soil must drain well but also retain moisture. Normal potting soils used for greenhouse growing may hold too much water in our wet summers which can then lead to potential root problems.

Container shapes and sizes can vary but the shallower squat-type or mum pots are popular as they sit closer to the ground and are less apt to blow over in the wind.

Plant one cutting per 8” or 9” pot. You can use two plants per 10” or three in a 12” or 14” pot. If making mum combos in the same pot be sure to use the same series so that plant habit and bloom times will match.

Water mums in with fertilizer immediately after planting. They are heavy feeders and will take well to a constant liquid feed (CFL) of 300 ppm with each irrigation.

Begin with a 20-10-20 type fertilizer for the first half of the crop which will initially make the plant grow lush and promote lateral branching which will set the stage for a good round shape once the plant finishes. These high levels of fertilizer early in the program will go far in determining the final size of your crop.

For the second half of the growing season, I find it works well to use a mum fertilizer that is low in  phosphorus. High levels of phosphorus can cause stretching and weaken stems. A mum fertilizer such as Jack’s 22-5-16 also has additional magnesium, sulfur, and iron to help keep leaves green even if the pH begins to creep up. The chelated iron in this formulation makes itself available to the plants even with a higher soil pH that so often occurs later in the crop. At this time, a rate of about 250 ppm CLF should be given till mums are sold.

You can incorporate a time-release fertilizer (Osmocote) into the soil, but liquid feed should also be given. The recommended rates here can vary depending on how much liquid fertilizer is provided.  Because the time-release fertilizer can release very fast at high temperatures, I would recommend using just a constant liquid feed instead. This also helps acidify your irrigation water to keep the pH down near 6 where it needs to be for the best growth and color.

Watering with a drip irrigation system rather than overhead sprinklers can cause foliar diseases, especially later in the crop when a heavier canopy of foliage exists.

Never allow plants to become stressed due to lack of water. This will cause stunting of growth, premature budding, and lead to branches breaking off at the stem when the plants mature and flower.

A mum’s final footprint will depend on many factors such as pot size, when planted, and how well the crop is grown. Typically, 8” mum pans will have a footprint of 24” X 24” if grown to their full potential. In 9” pans you can figure from 24” to 30”  centers.

It is best to not let mums touch or, due to lack of sun and air movement, lower foliage can begin to decay.

With very few exceptions, pinching is not needed with today’s cultivars. They will branch well when grown in full sun with ample fertilizer during the first half of the crop. Again,  higher levels of fertilizer (300 ppm) early in the mum crop will determine the final size of that crop.

As with any ornamental crop, diseases can be an issue. The best precaution is to do your best to keep the mum area clean and the plants healthy. Avoid stress by planting as soon as possible after receiving cuttings and then fertilizing at about 300 ppm,  tapering off to 200-250 ppm after the first month or so until sale.  Plants are like people. They need good nutrition to stay healthy.

Several root diseases can affect mums. Pythium, Rhizoctonia, and Fusarium are the most common. It is good to use a preventative fungicide to make sure your plants remain healthy. As a general preventative, I recommend  Banrot which is a very good broad-spectrum, inexpensive fungicide. Be sure to use this as a soil drench soon after planting.

Foliar diseases can also rear their ugly heads during our long, hot, humid summers. Avoid overhead watering and give ample space between plans to encourage air movement throughout the crop. Treatments here can be difficult and expensive so please take all mentioned preventative steps to avoid such situations.

With any crop, it is always good to make notes and if certain varieties do not perform well for you, make changes for the following year.

Few insects are an issue for mums grown outside. The weather and natural predators go far in keeping your mums clean. Caterpillars are probably the biggest concern, usually showing up in the middle of summer as the progeny of seemingly harmless butterflies and moths. Their green and brown colors blend right in with the foliage, and they can be difficult to see until leaf damage is done.  Any Bacillus thuringiensis product, such as Dipel or Thuricide, works on these pests. These (BT) are biological organisms that will prevent the caterpillars from passing food through their systems.

Other pests can be concerning as well. Aphids,  white-fly, and thrips, while not common on outdoor mums can occasionally be an issue. Here many will use an imidacloprid pesticide such as Safari or Marathon as a preventative. If you go this route, please apply early in the crop so that there is no danger to foraging bees when the blooms open in late summer or fall.

As with any other crop, scouting and a watchful eye go far in catching these populations before they become an issue.

Heat Delay:
Heat delay occurs when night temperatures are very high (80F plus) for prolonged periods of time after flower buds have initiated. At these high temperatures, flower buds will often not develop as they should. This can delay flowering in some cases and decrease flower counts in others. This can vary by variety so please take notes and remove from your program those varieties that do not perform well. There is little that you can do to prevent heat delay.

Crown Budding:
Crown budding occurs when premature flower buds form prior to when they should. This is usually caused by stress due to extreme weather, adverse growing conditions, or both. Water stress to the point of wilting and low fertilizer levels can both cause premature budding. Also, if several nights of cool temperatures occur before natural flower initiation, premature buds can form. Quite often, if ample water and fertilizer are given, mums will be able to outgrow minor cases of premature bud-set. It is best to prevent this condition by growing your mums with adequate fertilizer and stress-free growing conditions.

Be cautious when growing mums near farm fields or other areas where broadleaf herbicides are applied, as the drift of many of these chemicals can potentially cause problems for your mums.

If you are doing something with your mums that is different than what is shared above, and all is going well, please continue to grow as you have. Perhaps modify, experiment,  and consider other options, but be cautious before changing something that works. Successful growing is not a black and white science. It is the result of general guidelines, one’s own experience &  observation, as well as a plethora of many other variables. Some of these variables we have control over and some we do not. The above is only meant as a guide to be considered with caution and a watchful eye.

If you need help or elaboration on any of the above topics, please feel free to contact us.  If you need a source for or advice on annuals, perennials, pH or EC  meters, soil or anything else, I can help you with that as well.

Happy Growing!

 Mike Hellmann
Plants and Cuttings Manager
 P.S. Curious about my background and how I got to Hummert? You can find out more here.

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