Forty Under 40 Perspectives: Frost protection using irrigation By Zach Brown

When I began working at Bailey Nurseries as an assistant foreman in plant health, I had a lot to learn despite a degree in horticulture and 10 plus years working in the industry. The scale at which this company grows plants can be very intimidating, and I learned there were many factors that needed to be considered and tracked throughout the year. 

Weather is always a factor with outdoor growing and dictates much of what we can do in the field each and every day. Seasonal transitions prove to be challenging as plants require different care. 

Spring is an exciting time for the industry. Plants are waking up and customers are ready to take delivery of plants. The volatile climate in the Upper Midwest can make this an even more exciting time. We can often see daytime temperatures in the 60’s and 70’s with overnight temperatures well below freezing. Because of these large temperature swings, frost protection for plants is a yearly concern for us. 

One major tool we use for this is our irrigation system — to ice plants. By doing this, we are able to provide protection for vulnerable plants in freezing temperatures (down to about 25° F) by running water over the top of them. When the water changes from liquid to solid form, the process gives off a small amount of heat. This process provides just enough heat to keep the plant tissues from freezing under the layer of ice, preventing damage to the foliage. When temperatures rise above freezing, the ice layer will melt away signaling us that the plants no longer need the irrigation protection and to turn the water off. 

Zach Brown (right).


In the plant health department at Bailey Nurseries, we pay close attention to forecasts for the temperature, dew points and wind speeds. When the three are forecasted to be low, frost is likely to form in the field. When frost is expected, we prepare for potential icing events, including many discussions about the various forecasts and what they are calling for. 

We plan based on the growth stage of various plants as well as our capacity of protection in the field. Using a combination of fabrics and irrigation, we attempt to protect anything that has tender new growth from the warm daytime highs. 

It is during our planning when we decide which plants will get water and which plants will get a fabric covering. Our normal capacity for an irrigation setting is roughly 25 acres. This isn’t very much considering we have over 130 acres under irrigation. We always have to prioritize and treat the most vulnerable varieties with water while the rest receive fabric protection. 

The days leading up to a cold snap require a great deal of preparation. The irrigation system is prepared and set up so that when the temperature reaches 35° F, we are able to turn pumps on and start moving water. 


When an icing event is necessary, these events usually start in the middle of the night as the temperature cools and the winds die down. Once the temperature reaches 35° F, the irrigation system must be started or we might encounter complications with the equipment due to the low temperature. In a typical year, the plants that are most at risk for us are Hydrangea arborescens, Hydrangea macrophylla and taxus. Each of these crops quickly form tender new growth that can easily burn when frost forms. 

Once the system is on, the staff running the icing event will drive around to make sure the sprinklers are rotating and free of clogs, which can be a difficult task to do in the dark. With a set list of functioning lines, the person tasked with the overnight shift is able to check and recheck things. 

Water usually runs for an hour or more before ice starts to form on the plants. Once the ice forms, we look for clear ice. This tells us that the coverage is good, and the ice formation is going to protect the plants underneath. We have spent many nights over the years driving around the farm to ensure that we have uniform ice coverage throughout our facilities. 

An average icing event will last six to eight hours, but one event in particular lasted several days. Once the system was turned on, the temperatures never rose enough for the ice to start melting. The safest thing to do was to keep the irrigation running until the temperatures warmed and we were in the clear. This definitely made for a few stressful days! There is no better feeling during this whole process than when the sun comes up and people start to show up for the workday. It provides a second wind and lets us know that with the sun comes warmth. 

Speaking from experience, this is a tedious but necessary process. All of our efforts that go into growing these plants can be wiped out in a matter of minutes if we don’t plan and prepare for the cold temperatures. Having the option of protection like this is critical for our business. Although skeptical of frost protection at first, I have since become very comfortable with the process and can attest to its success. I wouldn’t say that we’ve mastered frost protection, but we’ve definitely had our fair share of experience with it.