Backyard Frost Protection by CRFG

loslunasfarmsApril 30, 2010

The Christmas weekend freeze of 1987 had a sobering effect on my enthusiasm for growing many of the conditionally adapted exotic fruit trees here in Southern California. My recorded temperatures dropped to 27 F and stayed below the freezing point long enough for a pail of water to form a quarter-inch thick cap of ice (freeze damage depends on the temperature and duration). The frost-scorched leaves of the rose apple, mango, guava, babaco and pepino dulce reminded me that to succeed in growing and fruiting these plants, protection must be provided against severe cold spells.

This is something commercial avocado and citrus growers are well aware of. They protect their trees using wind machines to keep cold air mixed with warmer layers, or do so using orchard heaters. While these technique aren't practical for most hobby growers, I know of at least a dozen things one can do in a small-orchard situation. They can be grouped as preconditioning procedures and freeze-response procedures.

Preconditioning Procedures

Preconditioning prepares the plant to withstand cold temperatures without damage. To toughen plant tissues in the late fall, do not apply nitrogen fertilizer after October 15 [in southern California]. Any fertilizer application should be high in potassium, as this element is known to promote thick cell walls. Another nutritional technique is to spray all plant surfaces with kelp seaweed solution. I use Maxicrop dry concentrate at one teaspoon per gallon of water. Cytokinins present in the seaweed toughen the plant cell walls.

Experienced commercial growers are currently frost-protecting citrus, avocados and strawberries with anti-transpirant sprays. All the plant surfaces are sprayed prior to anticipated freezes, and the protection afforded is suggested to be from two to eight degrees (°F). Here is a list of the ones I know of:

Frost Away -- by Bonide. Available from Mellingers.

Wilt-Pruf -- by Wilt-Pruf Produces, P.O. Box 469, Essex, CT 06426.

Frostguard -- by Custom Chemicides, P.O. Box 11216, Fresno, CA 93772. Available from local farm suppliers.

Frost Shield -- by Maz-Zee S.A. International, P.O. Box 82717, San Diego, CA 92138. Available from Peaceful Valley Farm Supply.

While I haven't been able to pin down any of the manufacturers as to how their products operate, it's safe to say that these products reduce the cooling effect of wind on leaf surfaces (chill factors).

Another approach to increasing the low-temperature tolerance of plants is by eliminating ice-nucleating bacteria (INB) from leaf surfaces. Recent research has demonstrated that some plants, which usually succumb at 30° F can be supercooled to 24° F without damage if these bacteria are eliminated from the plant's surfaces. As explained in the literature, these bacterial promote the formation of ice crystals that pierce plant cell walls, leading to desiccation and death. While not a completely accepted method, these bacteria can be killed by spraying plant surfaces with a bactericide such as Kocide 101 (cupric hydroxide).

Having preconditioned your trees with all these sprays, don't forget to protect the trunk and major branches. This is vitally important for trees in the ground only a year or two. The trunk, especially near the graft union, can be effectively protected by covering it with one of the special products made for this purpose. One type of tree wrap comes in a roll and is made of treated paper; another is a spiral ribbon of white plastic. Both products are available through mail-order farm and garden companies.

Exploiting the Heat of the Earth

On a cold night with air temperatures in the twenties, the earth's surface at 52° F is like a giant heater. To fully exploit that heat the ground near the tree should be cleaned of both mulch and growing weeds. It should be wet and uncultivated to maximize heat transfer from earth to air.

You may have noticed that plants placed under the leaf canopy of a large tree or a building overhang escape serious freeze damage, while those out in the open are killed. These covers contain the earth's heat.

I build a protective cover for most of my sensitive trees using a a wooden framework covered by shade cloth--beware of using clear plastic. The poles can be 2"x2"x8' lumber with the one end sharpened., and the wood treated with a preservative such as Waterseal. Four poles are driven into the ground in a 4-5 foot square pattern. I always use a steel pipe to make holes for the poles so as to avoid splitting the pole tops. The top ends are then joined with four 1"x2" boards using nails. I cover the framework with 50% shade cloth on top east and west sides and 75% shade cloth on the north side. I leave the south side open. This protector can be left up in summer for those plants needing it. The north side protection reduces the chilling and drying effect of winter winds. A similar approach which reportedly protects plants is to enclose the entire plant with a product called Agrinet. This material is very light and is easily supported by the tree's limbs. It is also available from mail order suppliers.

Exploiting the Heat in Water

We were taught in high school physics that water stores heat better than any solid material, and that it releases 80 times as much heat (heat of fusion) in changing from liquid to ice at 0° C (32° F) as it does when cooled one degree Celcius. That is why farmers water their orchards during a freeze, and so should the backyard grower. The water coming out of the pipe is probably at about 52° F (11° C) and gives off 11 calories per gram when it cools to 32° F (0° C), and then gives another 80 calories per gram when it solidifies.

Another way to exploit the heat held by water is to surround the tree with five-gallon plastic pails filled with water. This simulates the protection given plants near a body of water, such as a swimming pool.

© Copyright 1988,1998, California Rare Fruit Growers, Inc.

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Loslunas, I lay the pots on its sides. How much this help I have no idea. Sometimes I put a tarp over them & it sure raises the temp.-- the difference inside & outside the tarp was easily felt. This option helped me when we had an artic cold front with wind chill at least in the 22-16*F during 1st week Oct 2009. The leaves were all fried on the first day of the cold winds and after a few hours(2nd day) on putting up the tarp I went & check, it was warm in the enclosure. Most figs were affected except for Hollier, Marseillies VS, Slocan & Tony's Greek.

    Bookmark   May 1, 2010 at 12:22AM
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fruitnut Z7 4500ft SW TX

While the CRFG piece has some good information, some is also of questionable value. The pre-frost sprays would certainly fit into the questionable category. I really don't think many commercial growers are using them.

Also wind chill has no effect on plants at least not in the way it does for warm blooded animals. Wind chill is only a factor for a body that is appreciably warmer than air temperature. Fruit tree buds follow air temperature pretty closely whether the wind is blowing or not. In fact at times, as during a radiation freeze with still winds, bud buds can be colder than air temperature. So if the wind were blowing the buds could actually be warmed by the air. This is part of the effect of running fans during a radiation freeze with an inversion. The fan moves down warm air from above. The warmer air and wind movement warms the buds.

    Bookmark   May 1, 2010 at 2:59PM
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Thanks for posting that information. I had seen it before when you posted it sometime back. It a good reminder and very applicable at certain times of the year. Some of these practices are indeed used by me the many Citrus growers in my area. They do work quite well. It is a well kept secret that Louisiana does indeed have a small (compared to Florida and California) Citrus Industry. The taste of Louisiana citrus rivals the fruit that is grown in Florida and California because it has a better sugar to acid ratio. Our farmers did a great job of protecting MANY citrus trees from the unusually cold winter that we had in our area this past season. I lost some but saved most of my citrus from the cold temperatures that we experienced.


Wind chill is a function of both AIR temperature and its relative humidity level. And yes indeed, WIND CHILL CAN AFFECT PLANTS. Here is some technical information that I posted in another thread to help explain this multi variable phenomenon.

[This is FYI only and for those other forum members who might want to know some "WHY's" behind potential leaf damage due to is not just about AIR TEMPERATURE. It is also about wind, leaf temperature, and air humidity level. On a windy night with clear or cloudy skies LEAF temperature will be nearly the same as AIR temperature. However, on a cold, clear night with little to no air movement.....leaf temperature can easily drop 3 to 4 degrees lower than the ambient air temperature. (It can drop as much as 8 degrees in my area.) This is because of the RADIATION heat loss of the fig leaves. The rate of heat loss of those leaves is a function of the air's humidity level. At higher humidity levels often frost will form on those leaves. So, while the ambient AIR temperature might only be 35 degrees F......the actual LEAF temperature might well be 31 to 32 degrees F. That temperature could affect tender new growth.

In my area it is not uncommon for us to see frost form whenever the ambient air temperature is at 40 degrees F or below. This means that the actual leaf temperature reached 32 degrees F or below which froze the dew that condensed on the leaves as the dew point of the humid air was reached during the night. Late Spring frosts can kill fig trees in South Louisiana......especially if the outside air temperature has been cycling through several periods of warmth and cold. Yes, in my area, damaging frosts can form on fig leaves with ambient temperature as high as 40 degrees!! Ask me how I know and what I fear most at this time of year. Potential plant damage is really about leaf temperature and that is a bit harder to measure.]


    Bookmark   May 6, 2010 at 11:03AM
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fruitnut Z7 4500ft SW TX


I know that you know what affects figs in your area. But your explanation did nothing to convince me that wind chill affects plants. In fact you are saying the opposite. You said that leaf temperature can and will drop below air temperature when there is no wind. I agree. But that is exactly the opposite of wind chill as most people think of it. If the wind came up on a cold clear still night, the wind would warm the leaves. That's the opposite of what wind chill does to people and animals.

I'll agree with your last sentence: plant damage is about leaf temperature not air temperature. It's just that in a radiation freeze, wind is your friend, not your foe.

    Bookmark   May 6, 2010 at 10:07PM
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I agree with you. Wind chill makes temperatures seem even colder than they really are. Animals and humans feel colder because the wind makes moisture on their skin evaporate, removing their body heat. The faster the winds blow the greater the wind chill.....this is due to EVAPORATIVE cooling while what I explained above is due to RADIATION heat loss....entirely different mechanisms.
Thanks for setting me straight.


    Bookmark   May 6, 2010 at 10:40PM
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Thank you for posting these ideas.

One of the many reasons that I keep my fruit trees pruned to compact size, is that it helps me deal with Mother Nature's challenges. They are small enough that I can cover with nets to avoid birds. Plus, it lets me have more varieties. In addition, I can cover with an old blanket if frost is expected, when the tree is at a sensitive moment.

This may be a reason to prune to bush, instead of tree, shape, although I haven't done that.

I have also used wilt-pruf. It was not a scientific experiment, but it gave me the benefit of thinking I was doing something useful, whether or not it was.

Not for figs, but when my peaches were blooming and a frost was expected, I covered the trees with a blanket, and placed buckets of warm water under the blanket, as you mentioned. Frost on a blooming peach tree can kill it, even if it survives hard freeze when dormant. Seemed to help, or it might have been my imagination.

I've read with interest when others write about having Xmas lights in the tree for warmth. I need to get some at a yard sale, ours are the non-heat twinkly types.

Thanks for the advice.


    Bookmark   May 7, 2010 at 12:09PM
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.......posted this in another thread:

Early watering of trees before a night time freeze ABSOLUTELY does give some protection in a "dry" climate or in any area of the country, for that matter, during a period with a low outside relative humidity. I would do exactly what Jose did to INTENTIONALLY increase the relative humidity around my little in ground trees. Water vapor is by far the largest green house gas that we made or other wise....(Al Gore and his Global Warming crowd & our news Media would prefer that you not know this science fact). By increasing the water vapor in the areas around these trees, you WILL effectively trap some of the ground's "radiation" heat around those trees. What is trapped by this added water vapor is some of radiation heat that is quickly lost to the atmosphere after the sun goes down. Ever notice how hot a desert is in the daytime......and then how cold it is at night???? This large variation in temperature occurs simply because there is no humidity (water vapor) in the desert air. If there was some water vapor in the air, the daytime and night time temperatures wouldn't swing as much. If you could somehow increase the relative humidity of the desert air, it simply would not get as cold at night.....nor as hot during the daytime.
I do agree, however, that there is also some good benefits to watering at the time of coldest temperature (closer to sunrise)....due to the latent heat of fusion effects that occur right at the freeing point (melting point) of water as it starts to change from the liquid phase (water) to the solid phase (ice). Too, it is because of this same latent effect that provides protection to fruit trees that have ice already on the branches. Keep the water sprinklers on even when you see ice (or frost) on the leaves and branches and this latent heat will keep the temperature from dropping below 32 deg. F.........that is a warm enough temperature to save a lot of trees from severe damage.

Too, if somehow you can't prevent plain ole frost from forming on your trees (which can easily occur at temperatures as high as 40 deg F in my area)..........get at them with a sprinkler or hose pipe as soon as you see it and you WILL PREVENT some damage. I can get these kinds of "surprise" frosts in my area once in a while when the weather man was a bit off with his forecast.....


    Bookmark   May 9, 2010 at 1:54AM
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Sorry for the "bump up" but this is always relevant info.

If you use water in Soda bottles, Buckets or Pails then put a piece of Back Plastic in the water.
The sun will warm the plastic and the water will become much warmer than without. I tried and the temp difference is quite high.

    Bookmark   May 24, 2012 at 10:35PM
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noss(Zone 9a Lafayette, LA)


Don't apologize for bumping this thread up again. It gave me the opportunity to put it in favorites. I am not sure I've seen it before, but if I did, I don't remember it.



    Bookmark   June 5, 2012 at 2:40AM
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