Tips and Tricks for Outdoor Mum and Hydrangea Production this Summer

This post was co-authored by Dr. Jeanine West, Flowers Canada Ontario’s Environment Specialist

outdoor 6Do you grow hardy mums and hydrangeas outdoors?  If so, this blog post is for you!  Flowers Canada Ontario, the Soil Resource Group and OMAFRA have collected data about fertilizer and water management in outdoor greenhouse crops over the last few summers, and have some updated production information for growers to think about over this year’s season.

The goal of the study was to look at ways to improve fertilizer and irrigation efficiency outside of the greenhouse.  We looked at several mum and hydrangea fields throughout Ontario,and measured the amount of irrigation each crop received.  This included irrigation from rainwater and either drip line or overhead sprinklers. The amount of water that passed through each pot after an irrigation event (leachate) was also collected and measured. Some crops were fed with water soluble fertilizer (both overhead and through drip irrigation lines), while others used incorporated controlled release fertilizers and were irrigated with just plain water.

The key findings from the trial were:

  1. The irrigation method has a major impact on the potential for lost nutrients
  2. Fertilizer choices can improve environmental performance without risking crop quality

The major take away was pretty simple and something that you might have already suspected: If irrigation volumes aren’t managed, high leachate volumes can occur.  This may translate to wasted money on fertilizer products. While these finding might not be surprising, they do remind us that knowing what is happening both inside and outside the greenhouse is important!

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A fall mum on drip irrigation. The plastic pail below the pot allowed us to measure the amount of irrigation that was not captured by the plant.

While the actual amount of irrigation used depended on the operation, those farms using drip line irrigation typically used less overall, and had more uniform water distribution.  In terms of fertilizers, the amount of nutrients staying with the plant were highest when controlled release fertilizers (CRFs) were used and lowest when water soluble fertilizers were applied in high volumes by drip line.  These results show us that unless irrigation practices and systems are tightly monitored and controlled, environmental risk can be significantly reduced by using controlled release fertilizers.


Best Management Practices (BMPs) for Outdoor Greenhouse Crops

  1. Irrigation Method:

Use low volume drippers where possible.  Know your application volumes and irrigate based on crop needs, not a set schedule. Good management practices include tracking weather patterns, monitoring crop health and using well-maintained equipment (i.e. unclogged drippers, working valves, lines that have been cleaned thoroughly).

Note: Low volume drip line will only reduce volumes and risk if they are used properly! A “set it and forget it” approach doesn’t work.

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  1. Fertilizer choice:
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

How can I track my own irrigation efficiency?

Unsure of exactly how much water is reaching your pots?  This is an area to focus on if you have a limited water supply, and/or are looking to save on water and fertilizer costs.  A quick and dirty way to figure out your own irrigation efficiency is listed below.  This method is also useful for identifying dry and wet spots in the field, before they become a problem.

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An example hydrangea site in a Cravo-house with overhead sprinkler irrigation system. Sample pots (placed in blue buckets to collect leachate) were chosen randomly and sampled weekly over the summer. Irrigation & rainwater were also tracked.

1.      Gather a number of pots or buckets that will tightly fit under the plants you have outdoors. Ensure they don’t have holes or cracks which will allow water to escape.

2.      Place them under selected pots.  Make sure your sample includes pots from a variety of locations in your field; e.g. close and far from irrigation equipment and both edge and inner rows of pot-tight plants.

3.      Ensure you have a way to collect rainwater. A rain gauge just outside the production area is your best bet; just don’t forget where you placed it!

4.      Make sure you can collect irrigation water separate from plants to see how much is actually reaching them.  Options include a separate dripper that feeds into a covered and labelled bucket or a larger container to collect overhead irrigation. Be creative – we used a few kiddie pools in our study!

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These hydrangeas are placed in plastic pails for leachate collection and overhead irrigation in the production area is captured by a pool. A gauge outside the production area collects rainwater.

5.      Determine when to collect data (we suggest daily or weekly), and ensure someone from your team measures the amounts in each container.  A plastic measuring cup or graduated cylinder works great for this purpose!

6.      Calculate your irrigation efficiency by using this formula: Take the average of all volumes collected from each leachate collection pail and divide by the total amount of irrigation applied per pot (dripper) or area (overhead). Visually this formula looks like:

% Irrigation Efficiency = (Average leachate volume/ Average irrigation volume) x 100

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Avoid playing “Where’s Waldo?” – make sure sample pots are flagged so they can be seen throughout the entire season. Remind staff that flags shouldn’t move.

7.      Look at the data to see how much water you are using.  Is it more than you expected?  Were the leachate pails usually full when you sampled? If so, consider backing off on your irrigation.  Switching to more frequent irrigation events with less volume may assist in improving your irrigation efficiency and save you fertilizer without sacrificing plant quality.

8.      Tracking weather patterns, pot weight and growing media dampness can assist in determining optimum irrigation levels.  Make sure a staff member walks the crop on a regular basis to identify these parameters.


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