The chilly mornings of early November usher in another season of frost and freeze warnings for area gardeners. In the Sacramento area, that could be as early as the first week in November...or as late as March 27. Typically, the Sacramento frost season extends through December and January. Check with your county's Cooperative Extension Office to find out your area's typical frost season.
Of special concern to backyard growers are citrus trees, many of which are currently producing oranges, lemons, limes and mandarins. Here are a few steps recommended by the University of California that might save your citrus trees from a mushy fate during prolonged cold spells when the nighttime temperatures could possibly plummet into the upper 20's for an extended period:
* If the citrus plant is in a container, move it to an area that may shelter it from the wind while providing some ambient heat from the side of a building.
* Make sure plants are well-watered, especially those under patio covers. The combination of dry soil and freezing temperatures can stress a plant beyond recovery.
* Move aside any mulch beneath citrus trees. This allows the soil to radiate heat back up through the tree during cold nights.
* Harvest any fruit that is ripe. Unripened citrus will not continue to mature if it is picked. Leave those on the tree.
* For citrus trees under three years old, wrap a thick insulating material such as fiberglass building insulation or old newspapers around the tree trunk. Replace it if it gets soaked.
* Build a frame around the tree, covering it with burlap or row cover cloth (polypropylene), making sure that this tent-like shelter doesn't touch the leaves. Foliage that touches the sheeting could be damaged by the freezing cold. Take the cover off during sunny weather.
* The larger sized Christmas lights or a couple of 150-watt light bulbs located in the central area of the tree may add two to four degrees Fahrenheit protection.
* Two low-emitting mini-sprinklers, ones that put out about a half gallon a minute, placed on opposite sides of the tree, may provide two to three degrees Fahrenheit protection. Turn on these low-angle sprinklers before the air temperature drops to 32 degrees and keep them on until the temperature rises above 32. But be sure that the sprinklers don't spray water over the trees; a buildup of ice can cause limbs to break.
What if your yard has already been hit by a blast of temperatures below 32 degrees? The best thing right now for many suffering plants might include a dose of benign neglect. Although some of the leaves may be drooping and turning brown, cold-damaged perennials and shrubs might come back to life with the onset of February's daytime highs in the 60's and overnight lows in the 40's. And, if another freeze settles into the area between now and late March (the latest date recorded for temperatures of 32 and below), those dead leaves, left on the plant, can offer a few degrees of protection for that perennial, shrub or tree. Feed them a balanced fertilizer in early spring; wait until mid- April before performing any burial ceremonies.
If a cold-damaged plant develops new leaf buds in late winter or early spring, recovery is near certain. But if there are no new buds, two tests can help you determine whether to dig out the plant or let it grow. If a branch looks suspiciously unlively, gently bend it in your hands. If it bends, it's probably still alive. Save your final judgment for that plant for a late April day. If that branch snaps in two, it's probably dead. But before you dig up the whole tree or shrub, try this test: Work your way back towards the main stem of the plant, trying the "bend or break" test on several branches. If you reach a point where the plant branches bend, prune out the dead portions that extend from that point.
If the branches keep snapping, don't give up just yet. On the trunk of the plant, lightly scrape away a small portion of the outer bark with your fingernail or a small knife; don't cut too deeply. If that inner layer (the cambium layer) below the outer bark is brown or black, there's a good chance the plant is a goner. If that inner layer is green, the plant still has life.
If temperatures are forecast to dip below freezing during the next few weeks, water plants thoroughly, especially sheltered container plants; move sensitive container plants next to a south or west facing wall; or, cover sensitive plants with burlap, row cover fabric or cloth sheets, removing them during the day.