Put a large black plastic drum (or a 44 gallon drum painted black) under each fruit tree and fill the container with water.
During the day the drum will heat up and throw off enough radiation at night stopping the frost from settling.
You can also espalier dwarf fruit trees against a north facing brick wall of your house then strawberries can be planted at the base facing the wall.
According to a NZ company who sells specialist frost protection equipment, the good ones sell for around $1800. But the bottom line is that that when the alarm goes off, they do not rely on the sprinklers coming on automatically – they get up at whatever hour to make sure that all is working as it should. I also spoke to the owner of a vineyard and they have just installed 2 propellers at $55,000 each which use 300 ltrs of diesel per night and around the base of the propeller they put 10 smokepots which generate a hit of heat that is taken up by the propeller. He said that the problem with the overhead watering system is that by the time the frost arrives, the pipes are frozen Ref: Sheryl Backhouse
Increase plant carbohydrate levels because higher levels of carbohydrates in plants during a frost event means less leakage, hence damage during thawing. Biological farmers measure “Brix levels” with a refractometer. Crops with a higher sugar content (high Brix) will also have a lower freezing point, with an associated protection against frost damage. The soil forms a heat bank, and we want warm soil for warm air rise at night to minimize frost risk. A high Brix reading means higher sugar and mineral content, higher true protein content, a greater specific gravity or density, and a lower nitrate and water content for better storage characteristics. The key to achieving high carbohydrate levels are canopy management and avoiding a high nitrogen status. The crop canopy will trap cold air on top, so a dense canopy is not necessarily desirable. Strategies for pulses evolve around these principles, and crop choice. Crops deficient or marginal in potassium and copper are likely to be more susceptible to frost damage, and this may also be the case for molybdenum. Foliar copper, zinc or manganese will only be effective if the crop is deficient in the element applied. Canopy management is important. In cereals, frost sits on top of the canopy when the cold air is trapped, and so damages the upper parts of the plant. Sowing in wider rows enables frost to get to ground level, and the inter-row soil is more exposed. The open canopy does not trap cold air. Wide rows require the soil to be moist to trap the heat in the soil during the day. With wide or paired rows and a wide gap, the heat can radiate up. Wide rows can be used to channel cold air by aligning the rows downhill. Channel air flow away from the susceptible crop by using wide rows aligned up and down the hill or slope. In some areas in WA, apparently a 3m wide “moat” is used to channel the cold air. A sacrifice area may be required where the cold air settles. Claying or delving sandy soils increase the ability of the soil to absorb and hold heat by making the soil colour darker, and retaining moisture nearer the surface. Claying can be an expensive practice and requires careful costing before treating large areas. Learn from vineyard experiences: In 2006 the vineyard experiences in the SE of South Australia (“Limestone Coast’) with severe frosts was that the only successful measure was use of frost sprinklers. Air movement through frost fans was inadequate apart from a few metres from the fan. Air did channel down the vine rows into low spots where worst damage occurred. Smoke was useless, and inter-row practices of little benefit in such a severe frost year. Ref: Wayne Hawthorne
I protected my cold sensitive plants this past winter by putting step ladders over them and then draping the ladders with quilts. Over smaller plants I upended wastebaskets and trash cans. If your plant is particularly sensitive, you can string Christmas lights inside your protective covering and the minimal heat from the lights may very well keep the temperature inside above freezing. Be careful with plastic. It can cook the plants underneath if the sun comes out the next day. Ref: Di Bauer
Frost protection cloth (or even the bed sheets over the plants) works by holding in the warmer air the earth radiates all of the time. That is why it is important to have the material go all of the way to the ground. If you just cover the tree branches themselves, there is no reservoir of heat to help protect the plant. It doesn’t work well, but if you are needing only 1-3 degrees F of protection, they are available to help. You should have covered all frost sensitive plants with at least bedsheets. Be sure they go from somewhat above the tallest part of the plant down to the soil itself. This seeems to give about 3 degrees F of protection. They also make a frost protection cloth but that is expensive. The sheets can remain on the plants for several weeks as enough sunlight gets through for photosynthesis to continue. Without protection, Surinam cherry and Cherry of the Rio Grande will survive to about 22 F. Kwai Muk will survive 28 F. Roger Meyer, southern California.
I am growing White Sapotes here in the Katy, Texas area. I have never protected my trees and they have survived, so far the following low temps 22, 24 and 25 degrees. The main thing I do here is try to make sure they are not putting on new growth when the freezes come thru here. I do not fertilize them from autumn and do not fertilize again until early spring. This seems to get them through the winter in pretty good shape.