In the Garden:
Southern California Coastal & Inland Valleys
December, 2009
Regional Report

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When using plastic sheeting for frost protection, keep it away from the foliage.

Frost Protection

The average first frost for Southern California is Thanksgiving, and the average last frost is the end of January. However, our gardening region is so broad and varied, with a multitude of microclimates, that some of us will have to deal with yearly frost, and others of us won't.

My Pasadena garden hasn't experienced a light -- much less hard -- frost in five years. Only this last year I decided to remove the five-year-old sweet pepper plants in favor of completely renovating the bed. I enriched the soil and replanted with cucumbers and squash during the summer, and now lettuce for the winter.

For those of you whose gardens may be threatened with frost this year, here are some tips to lessen damage:

-- Move dish cacti and succulents and potted trees under cover for protection from cold and rain.
-- Cover bougainvilleas, fuchsias, hibiscus, and other subtropicals with large cardboard boxes overnight, or drape old sheets or tarps on stakes over them. But remember to uncover them in the morning so the plants can continue their daytime photosynthesis.
-- Wrap citrus tree trunks with newspaper, and cover the foliage with plastic sheeting. Cold soil and dry winds can cause the rinds of ripening fruit to develop bleached blotches, and leaves to turn yellow where the sun strikes.
-- Use plastic sheeting to protect the southwest side of plants near the house from chilling winds.
-- When using plastic sheeting to cover plants, don't let it touch the foliage, as the foliage may freeze more readily since the plastic will conduct the cold directly to the foliage. The frost protection value is in the cushion of air between the foliage and the covering.
-- Cold air falls down, so covering the tops of plants is first priority. Enclosing the plant will protect it from cold winds. Remember to provide ventilation openings, so warm days don't result in steamed plants!
-- When hard frost threatens, sprinkle foliage with water so the layer of moisture remains on the leaves overnight. As it freezes, it forms an inner protective layer of air between the leaf and the frost. However, make sure to sprinkle again before the ice melts in the morning, so the spiky ice chards can't pierce the leaf cells as they melt and breach the air layer.
-- Continue to water your overwintering outdoor plants unless the rains keep the soil moist. Irrigation should be less frequent, but just as deep, as plant photosynthesis slows down and cold weather dries plants out. Plants that are stressed due to lack of irrigation are more susceptible to frost damage.


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