Frost is a major threat to stone fruit, citrus, and nut trees. It will damage the blossoms of young fruit and potentially damage or completely kill young trees. Microsprinklers like Fan-Jets are an effective method to prevent the temperature from dropping too low around vulnerable fruit buds.

Citrus leaves damaged by freezing temperatures.

Fan-Jet® Microsprinklers are our recommended choice for frost protection, made since 1977 by Bowsmith out of Exeter, CA. They produce a fan-shaped spray pattern in varying patterns depending on the need of the crop. Streamline keeps in stock dozens of distinct Fan-Jet styles: a wide range of spray patterns (full circle, alternating, butterfly, half circle) and flow rates (4.4 GPH – 29.4 GPH per emitter). We sell assemblies with tubing and stakes, pressure compensating devices, and replacement heads.

fanjet releasing 7.4GPH

A Bowsmith Fan-Jet disbursing 8.4 GPH (Gallons Per Hour) per tree.

Irrigation for frost protection works because heat stored in water coming from the ground is transferred to the field, limiting damage from a frost event. The water travels through the irrigation lines and is distributed across the field. Sprinklers cover the ground and trees with droplets of water. This reduces heat radiation away from the field and adds heat conduction toward the plants. Each water droplet loses its heat, conducting it to the surrounding crop, ground, and air. This can bring the temperature around the plants up to 2°F warmer.

Frost protection in the Central Valley can be set up with well water or reservoirs. It’s a good thing to consider the option for frost during the initial irrigation plan, as you may need to size the underground pipes to enable a higher flow rate. If your irrigation has already been installed without planning for frost protection, it may still be possible to install sprinklers every other row and every other tree, although it’s not as ideal as full coverage. Partial coverage still provides some manner of protection to the crop.

There are a few key factors to consider when using Fan-Jets for frost protection:

  1. Timing: It’s important to start before the frost event occurs. If the water in the lines freezes before water is running, the ice will cause blockage. Test your system early enough to ensure it is running properly.
  2. Duration: The Fan-Jets should be left on for the frost event to prevent temperature drop, preferably until sunrise.
  3. Application rate: A higher application rate helps raise the temperature, which provides more protection against frost. When the application rate exceeds your well output, consider whether you should add a reservoir.

Keep in mind that a frost protection system can be used outside of frost events. Some farmers find it useful to hit the root zones in the middle of the row for irrigation and fertilizer. They can also be used to leach salts and settle beds after cultivating.