Frost protection of Fruit
All gardeners are aware of the dangers of frost on young opening leaves and flowers of many types of fruit in spring. An orchard owner in the Clyde valley told me the story of how his father used to light barrels of oil under his plum trees on frosty nights! And in the late 50’s wind pumps and heaters were being used in some countries. The 2012/13 winter in Scotland was very prolonged, but it turned out to be very beneficial.The apple blossom was almost a month later than usual, missing damaging frosts, and many varieties flowered at the same time. The effective pollination period was thus very short but very effective! The harvest of 2013 was superb! its the more usual erratic springs which cause us the problems.
Our main worry is the early frosts catching Oslins and Scots Dumplings, and the late frosts in mid-May which can destroy the later flowering Worcester and Cambusnethan trees chance of fruit.
How do professionals overcome this?
1-The best answer of course is not to plant your trees in risky areas such as frost hollows or the bottom of slopes.
2-Secondly, choose known hardy varieties for your area, i.e. not fruit that is grown widely in the warmest areas of France or the South of England. Hardy varieties have been bred and are grown in places like Poland, Norway and Canada, and some well known British varieties are very hardy: Keswick Codlin, Golden Spire, Emneth Early for example. We are actively propagating a few very hardy Swedish and Norwegian summer apples…so look out for them in our catalogue.
3-Thirdly, you may try to cover your trees on frosty nights with fleece or blankets. I tried this one winter, but realised that a lot of buds get damaged in the process of constant removal – you have to let pollinating insects in to do their work every day!
Some experiments in the 1950’s proved that covering is ineffective by and large. They tried using an electric heater and running a hose every 15 minutes over the branches. By far the most effective treatment was to provide a fine mist spray over the flowers as the temperatures dropped. In essence, the water prevents the temperature of the flowers going below freezing by latent heat of evaporation.
These spraying experiments, by JH Jeffree ( RHS, 1950), resulted in achieving a good crop on adjacent sides of two apple trees that were receiving spray. The far sides of each were bare of fruit come the summer! The effectiveness of, and the spray coverage, was improved by using a rotating spray head on a long pole.
If you want to try this next spring, be aware that a lot of ice can form on the twigs and branches so watch they don’t break under the weight! A few props for the weaker branches may help. You may need to be doing a few night shifts from early April to mid May this year!
Jeffree,J.H., 1950, RHS FRuit Yearbook, 1950.pages 100 -104.
Some notes can also be found on : http://hos.ufl.edu/extension/stonefruit/frost-protection-orchards-0 and http://ucce.ucdavis.edu/files/repositoryfiles/ca1208p4-64660.pdf and also: