The San Francisco Bay area only has a few nights with frost a year. But these infrequent cold temperatures pose a threat to some of the sub-tropical plants that we like to grow- like Citrus, Bougainvillea, Hibiscus and Tibouchina. What can we do to help these plants during cold nights?
Especially for small, potted, or newly planted specimens, a little extra care will help them through the frost. Make sure your plants are well watered. Overhead watering, while making the leaves and stems wet, is appropriate in this situation. If they are in pots that can be moved to a sheltered location, near your house or under larger plants, do so. Otherwise, find three or four stakes that are slightly longer than your plant is tall, and put them into to ground around the plant’s dripline so that they can be used to drape plastic sheeting over your plant. Throw the tarp or plastic sheet over the stakes, creating an instant greenhouse. Check to see that the plastic hovers over the plant for the best frost protection, not resting on the plant. Be sure to take the plastic off of the plants the next morning.