Identify cold spots in the landscape by monitoring with thermometers
Identify plants at risk: citrus, succulents, and tender perennials, tropical and subtropical plants.
Have supplies ready: sheets, blankets or frost cloths, lights, wraps for trunks, thermometers, stakes or framework to hold covers off foliage. Frost cloths come in different weights that can provide 4 to 8 degrees of protection. Because the frost cloth allows some light and air to penetrate, it can stay on plants for a few days at a time. Frost cloth can lie directly on plant foliage.
Prepare tender plants: avoid fertilizing and pruning after August to minimize tender new growth.
Rake away mulch to allow soil to warm up during the day and radiate heat into the plant at night.
MONITOR weather forecasts and note how low temperatures will be and for how long.
Local frost: clear, dry nights, usually warms during the day.
Hard freeze: temperature inversion or Arctic front, can last for days or weeks, are very damaging.
When a frost is forecast
Move plants to a warmer spot next to the house or under a patio cover, especially on the south side.
Check that plants are well watered because dry plants are more susceptible to damage, and moist soil retains heat better than dry soil.
Cover plants before sunset to capture ground heat radiating upward at night. Remove sheets, blankets and other covers daily if it is sunny and above freezing to allow soil to absorb heat.
Add heat by using outdoor lights: A 100 watt drop lights or holiday string lights to interior of plant. Use the old C7 or C9 large bulbs, not new LED lights which do not give off heat. Old style holiday lights that give off heat can provide up to 3 degrees of protection. Use lights, extension cords, and multi-outlets or power strips that are rated for outdoor use and grounded (3-prong). Avoid connecting together more than three light springs in a line.
Wrap trunks of tender trees if a hard freeze is expected, using towels, blankets, rags, or pipe insulation. Also wrap exposed pipes the same way.
Harvest ripe citrus fruit. Generally, both green and ripe fruit are damaged below 30 degrees, but there is some variation by species.
For more information go to: cecolusa.ucanr.edu