During our recent freezes, we heard from TV reporters, including one from The Weather Channel, that Tampa Bay area strawberry growers saved their crops by sprinkling their fields with water.
These reporters usually mention that the coating of ice insulates the delicate flowers and fruit, protecting them from the cold. To the casual viewer that sounds like a logical explanation, but if it were the case, the growers could just run their sprinkler system until ice forms and then go back to bed.
What protects strawberry flowers and fruit is the heat that is released as the water changes from liquid to solid. To generate that heat throughout the freeze, which can last 14 hours, the grower must continuously water.
There are a few good reasons why you shouldn't try this trick at home:
1. Tap water is expensive. Unless you have a separate meter to measure water used for irrigation, you'll pay a sewer charge in addition to a use charge.
2. Strawberry growers have sprinkler systems designed to put out just the right amount of water. Homeowners, on the other hand, are likely to apply more water than is needed, or too little to be effective.
3. Using water to protect strawberries from freeze damage works well because the plants are small and pliable. Trying the same thing on shrubs and small trees may do more harm than good as ice buildup snaps limbs.
The more practical way for homeowners to protect their tender plants is to cover them with old sheets, blankets or commercial polypropylene covers during the late afternoon preceding the expected freeze. The covering should be anchored to the ground on all sides to prevent wind from blowing it off. Covering plants with fabric works by trapping heat as it radiates from the soil during the night. Thus the air on the inside of the covering tends to stay a few degrees warmer than the air on the outside.
Moist soil absorbs more energy from the sun than dry soil, so homeowners can increase the amount of trapped heat by making sure the soil under their tender plants is moist on the day before the freeze.
The reason freeze-susceptible plants tend to have less damage when they're under the canopy of a tree or porch is that the canopy serves the same purpose as a fabric covering; it slows the radiation of heat from the ground and keeps the air surrounding the plants a few degrees warmer than the air surrounding plants that are exposed to an open sky.