For cold nights ahead, here's a frost plan

Old-style Christmas lights can help protect a frost-sensitive tree, such as this container citrus in a display at the Fair Oaks Horticulture Center in October. (Photos: Kathy Morrison) 

What to do when temperatures dip below freezing

By Debbie Arrington

Monday's chilly morning was a brisk reminder: We're now in frost season.

According to the Old Farmer’s Almanac, Sacramento's greatest frost danger falls between Dec. 4 and Feb. 10. While most of our outdoor plants can survive brief periods at 32 degrees, it's when overnight temperatures dip into the 20s for an hour or more that's particularly destructive. That's cold enough to turn stored water in stems and leaves or juice in fruit to ice. It can reduce a begonia into mush or burst ripe oranges.

Be prepared for more cold nights ahead with a frost plan:
* Know which plants are most at risk: Succulents, ferns, tropical plants, citrus, avocados, cacti, begonias, geraniums, peppers and soft-stemmed perennials. Mark those plants that need frost protection with a visual cue such as a blue-painted plant marker as a reminder.
* It's usually warmer close to the house. Move container plants under the eaves and create a frost-cloth tent. Suspend frost cloth or cloth sheeting from the rain gutters with clothes pins, then anchor it to the ground. Tuck in plants before sunset and remove the tent during the day.

The frost display at the Horticulture Center also included a frost blanket,
 which should be pulled  completely over the plant when in actual use.

* Have on hand lightweight cloth insulation blankets or frost cloths (available at nurseries and home improvement stores) to throw over sensitive plants. Old sheets work, too. Use cloth; plastic lets in the cold. When tenting, allow some room for air circulation; that helps retain heat.
* If frost is in the forecast, water frost-sensitive plants lightly in the afternoon if the soil is dry. Moist soil retains more heat. Well-hydrated plants are less likely to suffer frost burn.
* Don't water succulents before frost. Extra irrigation actually increases their frost risk. Instead, cover them with frost blankets.
* Pull mulch away from frost-sensitive plants; it retains cold as well as moisture.
* Know your garden's cold spots. Plants stay warmer on mounds or in raised beds; the lowest point in a garden is often the coldest. Houses radiate heat, making warm zones. Plan and plant accordingly.
* If temperatures are forecast below 30 degrees for more than 30 minutes, harvest ripe citrus to avoid damage. Lemons and limes are the most at risk.
* Lime trees are the most frost-sensitive citrus, suffering damage at 29 degrees. Other citrus withstand a few degrees colder, but not much. Protect citrus by irrigating before nightfall, sheltering with frost blankets before sunset and/or wrapping the trunk with insulation. Rags, blankets, sheeting or pipe insulation works.
* String old-fashioned Christmas lights around tree trunks of sensitive trees. LED lights won't work; they give off no heat.
* If plants still get burned, leave damaged foliage alone. Those brown leaves will help insulate the plants from further harm.