Younsuk Dong, Ph.D., has been studying irrigation and water management in Michigan Christmas trees, and the data show there is a wide variation in precipitation patterns.

“This has made irrigation management more challenging because we don’t know how much rain we’re getting tomorrow or next week. This information is so important to determine when to turn irrigation on and how much,” said Dong during a 2025 Michigan State University Christmas tree webinar series.

Dong is an assistant professor and Extension specialist in the Department of Biosystems & Agricultural Engineering at MSU.

Too much or too little moisture can have serious impacts on Christmas trees. A lack of water in young trees may result in high rates of tree mortality and poor growth. Excessive moisture can increase nutrient leaching, soil erosion and promote a suitable environment for Phytophthora root rot.

Checking Water Volume & Distribution

To avoid these moisture extremes, growers need to make sure their irrigation equipment is delivering water at the desired rate.

Dong suggested using catchment to quantify how much water is being delivered. Catchment systems can be used for any type of irrigation, although it can be harder to catch water in a drip system.

“All you need are catch cups or graduated cylinders. Use a timer and wait for 15 minutes or an hour while running the irrigation and see how much volume you get. You can calculate in millimeters per minute or gallons per hour,” Dong said.

He emphasized that it’s important to make sure that the system has enough pressure for specific types of drips and sprinklers.

Once a grower knows how much water is being delivered, it’s time to check for uniformity. Poor water distribution can result in over- and under-irrigated areas, and it can be caused by chemical deposits in the system, old equipment or clogging.

Once again, a homemade catchment system can be used to check for uniformity of water distribution. Growers using center pivot or overhead irrigation can insert fence posts or T-posts throughout a field. Then, cut a half-inch PVC pipe into a four-inch section. Drill a quarter-inch hole one inch from the end. Place the PVC pipe section over the post with the hole at the top. Thread a zip tie through the PVC pipe, creating a loop that serves as a holder for a 32-ounce plastic cup.

Then, turn on the irrigation system to begin catching water. Keep it turned on for about 30 minutes, then measure the amount of water in each cup with a graduated cylinder.

For growers using drip irrigation, Dong suggested collecting water by inserting small sections of tubing with a slit cut in them at various points through the system.

“Hopefully, you will see a very similar amount of water across each cup,” Dong said.

The data can then be entered into MSU’s spreadsheet calculator (downloadable at tinyurl.com/299eb3fm). The spreadsheet will calculate what is called a uniform coefficient.

The rule of thumb is that if the coefficient is less than 85, the irrigation system needs improvement. For example, in a center pivot system, it will be necessary to check for leaks, check gaskets or possibly replace sprinklers. If the coefficient is between 85 and 90, there are some minor issues, and if the number is greater than 90, the system likely doesn’t need improvement.

The uniformity test is especially important for growers seeking NRCS EQIP funding. “If your system uniformity coefficient is less than 85, then you’re eligible to get the cost share,” Dong said.

Weather-Based Irrigation Scheduling

It’s also important to have soil tests in order to calculate the water holding capacities of a farm’s various soil types. Sandy soils, for instance, have a low water holding capacity; loam and clay soils have high water holding capacity.

Once soil types are known, download the MSU Irrigation Scheduler app, available for iOS and Android. Users sign up, mark their fields on the maps provided in the app, and then enter their soil types.

Weather-based irrigation requires an understanding of how much water is lost from the ground through evaporation and loss of water through the crop – a process called evapotranspiration. Irrigation is needed when evapotranspiration is greater than soil water plus precipitation. These data are baked into the app. It also takes data from the weather station closest to a given field.

“The app basically helps you track how much water has been removed and also provides recommendations on when to water and how much water is needed,” Dong said.

Christmas trees growers outside of Michigan can also use the app but will need to manually enter the weather data from their area.

Dong thinks this app can be especially helpful for growers who live in states that require them to keep track of their water usage. The app can also provide alerts for when it’s time to turn on the irrigation.

Sensor-Based Irrigation Scheduling

Sensors can also be used to estimate the moisture level in the soil. Water mark sensors are one common type which measure soil water tension (the effort that is required by the root system to extract water from the soil). As the sensor values increase, the root has to work harder to pull water from the dry soil. When the value drops, it means the soil is wet.

The idea is to use these data to help decide when it’s time to turn on the irrigation and for how long. The data can also be used to help ensure that irrigation water is concentrated in trees’ root zones.

Ideally, sensors are placed at multiple depths in the crop rooting zone, and changes in soil texture with depth are taken into consideration to calculate irrigation needs. The goal is to set them in places with average soil moisture.

“We hope to develop an app. All you would have to do is enter the soil information and different locations, and the app will give you recommendations for where to put the sensors,” Dong said.