Tomato transplants often have to endure some cold weather after they are transplanted into the field in the spring.  When cold threatens, there are a number of freeze protection methods discussed around the countryside.  Do they work?  Let’s examine a few of them.

Irrigation is a common approach for frost protection in some areas. Unfortunately, drip irrigation is of no use at all. The science behind irrigating is that the latent heat in the water is released to the plant, keeping the plant from freezing. Ice will form on the plants if freezing temperatures are experienced, and irrigation MUST be continued until temperatures warm up again and the ice has completely melted. This method is only practical for growers who have overhead irrigation equipment and a water source near the fields that need protection. Keep in mind that with the size of plants that we have in the fields at this point, water from an irrigation gun may be destructive to the young plugs.

Helicopters or air movement provides a mixing effect between layers of cold and less cold air, which prevents the development of frost pockets. This method is best used for short-term or overnight freezing temperatures. The benefit is limited under extended periods of cold temperatures.

Copper or hydrogen peroxide are bactericides which remove ice-nucleating bacteria from the leaf surface. Certain bacteria that naturally occur on plants act as ice formation nuclei and make the plants susceptible to frost or freezing damage at relatively warm temperatures (around -2 to -4°C). Under lab conditions, if no ice nucleating bacteria were present, freezing might not occur until -8 to -10°C.

In the field, experiences with these frost protectant products have not been consistent. Remember, most transplants should have had copper applied before leaving the greenhouse, so additional application would not be effective. Also consider that any product that you apply to the crop to kill bacteria is considered a pesticide and must be registered.

Keep in mind that frost is not the only worry under these conditions. The plants are being subjected to chilling (tomatoes experience chilling injury at around 41°F or 5°C), the physical stress of wind whipping and the dessicating effects of wind, not to mention possible sandblasting. The best strategy to combat this is setting the plug sufficiently deep under the best planting conditions that you can possibly achieve. The presence of grass wind strips, of course, will reduce the wind damage and may provide some protection from frost as well!