Garden Mums – 2020 Production and Protection Tips

praying mantis on garden mumsThis post was contributed to by Drs. Sarah Jandricic and Chevonne Dayboll.

Summer is in full swing, and so too are garden mums!  Although generally an easy crop, there several tweaks you can make to help save headaches AND money.

This post has information to help you optimize your irrigation, fertilizer and pest management programs in garden mums.

Irrigation Method Matters!

Given the large acreage often occupied by garden mums, your watering strategy is one place you can look to save money.

There are plenty of options for irrigation in potted outdoor crops, but not all are created equal when it comes to maximizing water efficiency.  Overhead irrigation by boom, or sprinkler is not efficient if your pots are not spaced tightly.  Canopy sizes in the later months of production may make this impossible, especially if you choose to go with final spacing when pots first move outside.  These methods of irrigation can also lead to pots that are too dry (not watered) or too wet (over watered). Plants can only use water that makes it into the pot, so low volume drip line or tape is a more effective way to delivering usable water to your outdoor crops.

Drip line irrigation can be a more efficient way of delivering water and nutrients to outdoor crops.

Remember drip line only reduces lost irrigation volumes if it is used properly! A “set it and forget it” approach doesn’t work. Look for kinked lines and clogged emitters, and make sure connections are tight. Know your application volumes and irrigate based on crop needs and weather patterns, not a set schedule.

Interested in improving your water use efficiency?  Check out this post on outdoor mum and hydrangea production that highlights how to calculate volumes used and applied in an easy way.

outdoor 3
A garden mum on low volume drip irrigation. The pot below measures water not captured by the plant, giving the grower an idea of water use efficiency.

Fertilizer Choices:

There are a few schools of thought when it comes to fertilizer types for garden mums.  Some growers prefer to have more control over crop nutrition and choose water soluble mixes.  The benefit of this is that mixes can be quickly changed if needed.  Others choose to use controlled release fertilizers incorporated into the growing media and then irrigate with water only.  Both have their pros and cons.

As with irrigation, its important to remember that nutrients that don’t stay with the plant can’t be used by it. The amount of nutrients staying with the plant are usually highest when controlled release fertilizers (CRFs) are used with carefully monitored irrigation.  They are usually lowest when water soluble fertilizers are applied in high volumes (resulting in a lot of irrigation running through pots) and irrigation efficiency is low.  To keep the fertilizer where you want it, it’s important to irrigate only enough to saturate the pot.  Both formulations have their pros and cons, so make sure whatever you’ve chosen is easily managed.

Water Soluble Fertilizers Controlled Release Fertilizers
  • Higher risk for leaching
  • Fine tuning advantage for production needs (i.e. need to green up before shipping)
  • Volumes of irrigation applied greatly influence the impact
  • Choose the right product based on your irrigation methods, formulation and the release curve
  • Ask supplier to verify the product and rate against your production needs before incorporating

Looking for more information on water and fertilizer use in outdoor crops?  Check out research summaries from Flowers Canada and the Soil Research Group.

Pest Issues:

The good news is that garden mums grown outdoors simply don’t get the same pest pressure as pot mums.  Why?  A lot of this has to do with natural enemy populations from surrounding agricultural lands that seem to keep a lot of pests in check – like the cool praying mantis I found in a mum crop pictured at the top of this post!  To conserve these free biocontrol agents, avoid spraying if you can.  If you DO spray, do yourself a favour and chose something that’s compatible with beneficials so you don’t end up with a bigger problem on your hands from secondary pests.

Some pest issues you may see (and their solutions) are:

-Thrips. Rarely a problem outside,  western flower thrips – and even onion thrips – can affect garden mums grown indoors. Unfortunately, this species of chrysamthemum generally does NOT tolerate the usual recommendation of oil dips for cuttings.  A better bet to reduce incoming thrips on this crop, which you should consider “sensitive”,  is dips in BotaniGard (see more details in this post on spring crops). After sticking, predatory mite sachets (1 per pot) are your best bet for long term protection for spaced plants.  Amblyseius cucumeris (rather than A. swirskii) is the more economical choice for this crop.  Given how quick the crop grows, penetration of the soil with drenches of nematodes may not be feasible within a few weeks, so a good secondary measure is foliar applications of Beauveria-containing biopesticides (BotaniGard, BioCeres), if needed.  Growers also use a high density of large mass trapping cards in this crop, to help avoid thrips infestations that come from fly-ins in summer.

cards in mum crop
Large, yellow mass trapping cards can help manage thrips, especially those entering the greenhouse from surrounding agricultural lands in summer. A density of 8 cards/1000 square ft is suggested for floriculture crops (approximately 4 per bench).

– Aphids. We sometimes see these pop up in garden mums.  If they do become a problem, it seems to be later in the season (late Aug/Sept), so wait to apply pesticides until you actually see them (this also helps avoid unnecessary applications!).  Beleaf (flonicamid) is a good option as it’s a) soft on beneficials and b) can be applied via drench through irrigation lines, and c) is cheap!  Altus is a newer registration that is also a good option for aphids and other sucking pests.

mum sachets
One mite-sachet per pot provides protection against thrips when garden mums are grown inside. Remember to tuck your sachets within the plant canopy to provide the right humidity for optimal performance.

-Tarnished Plant Bug (also known as Lygus bugs) can be an issue in August, once buds form.  This pest is especially damaging, as their bud feeding causes severe flower deformation. Frequently, one variety or one side of the field gets hit first. Make sure to walk the crop regularly and look for adult bugs and aborted petals on open flowers  (pictured below). TPB can be controlled with pesticides applied for other sucking insects (e.g. aphids).

TPB on garden mum
Top Left: Tarnished plant bug (TPB) adult. Right: Garden mum flowers showing the aborted petals that are characteristic of TPB feeding. Bottom Left: a TPB adult feeding on a bud.

-Leafhoppers. These can fly in from the same surrounding agricultural lands as your free natural enemies, and can seem like an issue since they jump around plants a lot as you pass. The good news is they don’t seem to do any real crop damage.  Resist the urge to spray, and simply make sure your workers give plants a good shake to dislodge any adults before packing.

– Japanese beetle. While generally not a problem on garden mums, recall that all plants produced outside from June 15 to September 30 need to be treated for JB if you plan to export or ship to a JB-free zone. See this post for details.

-Diseases. Chrysanthemum white rust – a quarantinable disease – is theoretically possible, but has only been detected in Ontario once in the last decade thanks to regulations requiring plant material be sourced from white rust-free facilities.  Still, many growers treat as a precaution with Nova (mycobutanil), especially when exporting.  Other diseases, such as bacterial blight, Fusarium, Pythium and Rhizoctonia are more common, but generally aren’t big issues in Ontario production.  If problems develop, a good guide to disease symptoms and cultural management in garden mums can be found here.

Want to improve your natural enemy predation outside? Some growers in the U.S. use banker or “companion” plants such as alyssum, calendula and borage along field edges to attract parasitic wasps, Orius and syrphid flies.  Check out research from the University of Vermont.


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