Posts Tagged: freeze

Farmers, backyard gardeners brace for freeze

A very cold airmass from western Canada is moving into California tonight, reported the National Weather Service. With a hard freeze forecast, farmers and backyard gardeners are advised to prepare for temperatures that could damage their plants, reported the Sacramento Bee.

Homeowners should check for plants that are likely to be exposed to cold temperatures, said Judy McClure, UC Cooperative Extension master gardener coordinator.

“The lower spots in the garden tend to get colder than higher spots,” she said. “The bottom of the slope will be colder.”

McClure advises having a good supply of covers. She recommends against throwing a plastic tarp over trees, unless there is a frame to keep the plastic from direct contact with the tree. Contact with the plastic could cause damage by burning the foliage, she explained.

If the soil is dry, McClure said, it is best to water trees and succulents before covering them with blankets or frost cloths. When covering citrus trees, make sure the cover reaches the ground, she said.

The Fresno Bee reported that private meteorologist Steve Johnson has been tracking the approaching weather system since Nov. 25.

"The trajectory keeps it over land and it dries out," Johnson said. "This kind of thing doesn't happen very often. The pattern is very similar to what we saw in December 1998 and 1990."

For more on freeze protection from UC Cooperative Extension, review the following links:

• Citrus freeze protection (home)
• Methods of frost protection (orchards)
• Protecting avocados from frost

California citrus farmers weather the freeze

It has been particularly cold at night in California for about a week, but it appears the state's citrus industry will emerge mostly unscathed, reported Oliver Renick on Bloomberg.com.

“The temperatures were not severe enough to cause widespread damage,” said Craig Kallsen, UC Cooperative Extension advisor in Kern County. “This is nothing out of the ordinary, so we’re able to handle this.”

Thermometers dipped about 10 degrees below normal overnight during the cold snap, but growers efforts to keep the trees warm with wind machines and irrigation appear to have been successful.

"We are not anticipating any damage in the navels, maybe very limited damage on the outer row away from the wind protection,” said Shirley Batchman, the director of government affairs at California Citrus Mutual. “Certainly nothing that’s going to affect the orange production.”

Freeze!

It's been so nice to be out in the garden. Buds are starting to swell on some shrubs, weeds are growing like gangbusters.  I'm so ready for spring; I just want to clean everything up and plant away.  But this time of year I have to stop myself from doing one particular garden chore.  Some of my plants are looking a little, okay a lot, bedraggled because of frost damage.  I could make them look so much better with just a few snips here and there. 

For example, here is my avocado Persea americana.  I started it from seed. It lives out on my back patio just under a patio cover. On nights I anticipate frost, I cover it with a sheet along with my dwarf citrus that also live on the patio.  It's not looking very happy right about now.  I think most of this is frost damage, but some might also be damage from the weight of the sheet on the little tree.  I'm itching to cut all that brown damage off.  However in Solano County on average, our last frost date is March 15th.  We may get a few more frosts, yet.  Those ugly damaged parts are protecting leaves and stem lower on the plant.  If I cut the damaged parts off now that will just expose more of the plant to any remaining frosts.  So for right now, I just need to... step away... from the pruners.

Low temperature injury on avocado. (photo by Karen Metz)

Baby, It's Cold Outside

Is it a frost or a freeze? Honestly, it really does not matter. It is cold! But just in case you are curious, the difference is technical and meteorological.

A freeze (also called an advective freeze) occurs when a mass of cold air brings freezing temperatures into the area. For us, that normally means arctic air coming down from the Gulf of Alaska. It is usually cloudy and windy during a freeze.

A frost (also called a radiation frost) occurs under clear skies with wind less than five miles per hour which allow a temperature inversion to form near the ground where the temperature drops to freezing. Normally the temperature increases with altitude as you leave the ground. An inversion occurs when the temperature above the ground begins to cool at increasing height. If the air is very dry during a frost, no ice forms and it is called a black frost. A white frost forms when the air is holding water that condenses and freezes on surfaces forming ice.

Plants do not care why it is cold and the damage freezing temperatures cause depends on the species and age of the of plant and the amount of  time it is exposed to the cold temperature. Severely frozen citrus may drop off the tree while less affected fruit may look normal but be dried out inside. Tender growth on unprotected flowering plants may turn black once thawed and bamboo (Bambusa spp.) leaves may desiccate and fall off. Other plants such as mondo grass (Ophiopogon japonicus) may be completely undamaged.

If a plant is damaged, the best advice is to wait until spring before pruning out the dead material. Pruning now may lead to further damage from later frosts since damaged branches and leaves may provide some protection. Be patient and let new growth on the plant show you where to prune so you do not cut back too much. The last frost in our area is normally around the third week in March, but Mother Nature can be unpredictable!

For more information on protecting your plants from freezing weather, visit the UC Integrated Pest Management website http://www.ipm.ucdavis.edu/PMG/GARDEN/ENVIRON/frostdamage.html. A search for “frost” on the UC IPM website will also help you find examples of frost damage to many types of plants including fruits and vegetables.

frosty mondo

Central Valley farmers battle cold nights

Farmers in California's Central Valley have been taking precautions against freezing as nighttime temperatures have dipped into the low 20s in some areas, reported Tim Hearden of Capital Press.

From Dec. 3-10, temperatures dropped as low as 31 degrees in Fresno, 26 degrees in Madera, 27 degrees in Merced, 26 degrees in Napa, 25 in Redding and 27 in Redbluff. Growers in these areas were working to avoid damages like those suffered in 2007, when a freeze caused more than $1.4 billion in damage to citrus, avocados, strawberries, vegetables, nursery stock and other crops, the article said.

In northern areas, freezes blackened the tips of some young walnut tree branches, but those are generally pruned off anyway, said Rick Buchner, a University of California Cooperative Extension farm advisor in Red Bluff, Calif.

"There's been no serious damage in the big wood that I've been called to look at yet," Buchner said.

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