The best way to protect plants from frost is to plant varieties that can withstand the winter season, but this isn't always the case if you are growing fruit, herbs, vegetables or more tender varieties. There are some key things to keep in mind when protecting plants from frost--most importantly, how to water them before a predicted frost.
Water the garden thoroughly in the late afternoon before a predicted frost. In the evening, the soil will slowly release the moisture around the plants, keeping the airflow warmer.
Use an angled irrigation system for plants that are in poor-draining soil. This can prevent freeze damage when applied as a slow angled drip. You will want to avoid water hitting the foliage if the temperatures are below 32 degrees F, because ice will form on the branches and cause the limbs and foliage to break off.
Spray large clusters of plants or fields at dusk with water before a predicted frost. You want the ground to be saturated because it holds in and radiates heat much slower than dry ground.
Spray plants with water again around sunrise if the frost period is expected to be prolonged, such as six or more hours. This will remove any frost that may have gathered during the night.