More Frost Protection Tips for Citrus

Besides the frost protection tips for citrus and other plants mentioned in previous posts, here are some relatively inexpensive tricks for raising the temperature a few degrees around your young citrus trees during this frost and freeze season.

Tubular pipe insulation. Designed to keep your attic or basement water pipes from freezing, these can also protect the trunks of young citrus trees. One to three year old citrus tree trunks are very susceptible to freeze damage. The tree could die back to the root stock; but the root stock will quickly send up new shoots, resembling your pre-existing citrus tree...except for the nasty thorns, thicker leaves and ugly, tasteless fruit that rootstock growth will produce. Been there. Done that. Including a nasty thorn into the forehead. 

 

Remove the insulation at the end of the expected frost season to prevent any trunk rot issues from accumulated moisture.

Lights can be used to warm the tree. Shine an outdoor-approved 100 watt lightbulb on the large limbs or trunk to warm the most mass. The larger, older Christmas bulbs will work, too. Newer ones, although more energy efficient, don't produce as much heat as the older ones.

Put that tomato cage to winter use as a framework around a small citrus tree. Any blanket, including plastic, can be used at night to protect the tree, and not risk transferring the bitter cold to the leaves (which might happen if you just draped a plastic drop cloth over a citrus tree). But as the University of Arizona points out, remove that blanket during the day:

"If you use sheets or blankets, remove the coverings every morning when the temperature under the covering warms to 50 F. Permanently covering plants with sheets or blankets for the duration of the winter can be harmful. Even if the temperature under the drape does not warm up enough to 'cook' the plant, it is likely to warm up enough to cause the plant to break dormancy, begin actively growing, and thus become more susceptible to frost damage. However, many of the frost cloths available may be left on for extended periods without risk of harming the plant."

And, simply throwing a covering over a citrus is not enough, adds the University of Arizona: "Completely drape the plant from top all the way to the ground. Do not allow any openings for warmth to escape. This procedure will trap the heat radiating from the soil and maintain a more humid atmosphere around the plant foliage. Optimally, the drape will be supported by frame which does not allow it to touch the foliage. DO NOT gather the drape around the trunk of the tree. The goal is to trap heat being radiated from the ground, so ensure that the drape touches the ground at least as far out as the drip line.

And that brings us to one of the drawbacks of a relatively new frost protection product on the market, the frost bonnet: sort of a high-tech garbage bag, but made of a spun polypropylene fabric that cinches together at the top and bottom.

I'm trying these plant protector bags this year, but I am wary for several reasons: they are rather inexpensive (two 40" x 45" frost bonnets sell for about $8).

 

The warning label, in small print, is not very reassuring. 

 

And, even though you can safely leave these coverings over the citrus plants throughout the winter (or can you?), they look like the remnants of the Rotary Club's Saturday highway garbage cleanup drive. 

Oh, and because I forgot to anchor them securely to the soil, they blew off in a heavy wind last weekend.

And, a few really inexpensive frost protection ideas:

Keep the soil under the citrus tree well watered. Firm, bare moist soil absorbs more heat and loses it more rapidly than soil that is dry or covered with mulch or vegetation, according to the University of Arizona.

Think twice before purchasing anti-transpirants or other products to spray on your citrus trees for frost protection. According to the University of Arizona: "A variety of chemicals have been marketed with claims of changing the freezing point of the plant tissue; reducing the icenucleating bacteria on the crop (thus inhibiting ice and frost formation), or affecting growth (extending dormancy). To this date no commercially available material has withstood scientific scrutiny."

And if there is frost damage? Wait until late spring before reaching for the pruners. The damaged parts will be more obvious by then, so you won't accidentally remove healthy parts of the tree.

Thanksgiving Freeze Predicted. Is Your Yard Ready?

  Last week, we talked about strategies to protect your citrus trees from any expected mild frosts, when morning temperatures dip just below 32 degrees for an hour or two. 

     But what if the often predicted fall/winter freeze, when temperatures fall into the 20's for several hours each morning, settles into the area? The National Weather Service is forecasting overnight lows to dip below freezing, with many places just outside Sacramento falling into the 20's Tuesday, Wednesday and Thursday (Thanksgiving) this week. What else needs to be done in the yard to prep for a prolonged freeze when temperatures are forecast to fall to the upper 20's for several hours?
    
     Many of us learned this drill back in 1990, when consecutive low morning temperatures of 22, 18, 21 and 23 in Sacramento descended upon us during the period of December 21-24. Temperatures did not get above 25 degrees in parts of the San Joaquin Valley for three to five days and all time record low temperatures were set at Sacramento, Stockton, and Bakersfield. Many records were set for duration of freezing temperatures. The agricultural industry was devastated as acres of trees, not just fruit, were destroyed. Thirty-three counties were disaster-declared.

     Homeowners learned which plants don't like it cold (hibiscus, geraniums and other plants popular in the Bay Area and Southern California); and, which plants were the hardy survivors (another reason the oleander was chosen for the Highway 99 median strip). 

     Here's a last minute checklist for your home and garden if the TV weather people tell you tomorrow's low will be in the 20's:
 
• If it hasn't rained, water plants thoroughly, especially container plants.
 
• If possible, move sensitive container plants next to a south or west facing wall.
 
• Cover citrus and other sensitive plants with burlap, row cover fabric or sheets (be sure to keep the sheets dry). Tent plastic sheets over the plants; don't let plastic touch plant leaves. A light bulb placed in such a plant can offer a few degrees of protection.
 
• If using an anti-transpirant polymer coating material such as Wilt-Pruf or Cloud Cover, apply at the warmest time of the day, or at least six hours before an expected frost. However, research conducted at Washington State University concluded that these products may actually be detrimental to certain plants during a freeze. If using these products, thoroughly water the soil around the plant before applying.
 
• Disconnect hoses and drip lines, removing end caps. Lay out straight.
 
• To prevent broken grass blades, don't walk on a frozen lawn.
 
• Remove the lowest sprinkler head to drain.
 
• Cover unprotected faucets and pipes, including any spa or pool equipment.
 
• If temperatures are predicted to fall to the low 20's: prevent frozen attic pipes. Let lukewarm water trickle out of the indoor faucet farthest from the inlet. Also, let faucets with pipes running along an outer, north facing wall trickle during the night. 

• Ideally, add insulation to attic water pipes.
 
• Open cabinet doors to get more heat to the pipes. Close the garage door if water pipes pass through the garage.
 
• Setting your thermostat nightly at 55 can add needed heat to the attic pipes.
 
• If leaving the house for a Thanksgiving vacation during an expected freeze, turn off the water to the house, and open up the faucet farthest from the inlet. Be sure to turn off your water heater.
 
• To prevent cracking tile, run your pool and spa equipment during the freezing hours.

• Don't forget about your pets during a prolonged freeze. Bring them indoors at night. Move or replace their drinking water. Break up any frozen water in bird baths.
    
    

Their is some good news connected with a possible freeze: populations of yellowjackets, eucalyptus-feeding red gum lerp psyllids and grasshoppers could be greatly reduced in 2011.