Sprinkling on Top of Row Cover – How to Do It (12:25pm, Tue., 3/14/17)

— Written By Barclay Poling
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Sprinkling on top of row cover

  • You can sprinkle on top of the cover to add heat back into the ice blanket system, as we did for the Easter freeze of 2007. This technique can be very successful in windborne freeze conditions, or conditions where the row cover blanket is going to provide inadequate protection
  • For the ice blanket approach to work, you need a top notch sprinkling system, and you also need a digital thermometer to closely monitor bloom and bud temperatures all through the night. You really cannot tell if the sprinkling is helping or not without a digital thermometer and thermocouple wire that is inserted right into the blossom or bud.
  • When the temperature of bloom under the cover reaches 32-33 F, start the irrigation on top of the row covers (this temp reading in Fig. 2 is too low, and I would start sprinkling on top of cover by now lower than 32 F). This same unit is used for heat protection as well (Fig. 3).
  • After you start sprinkling on top of the row covers, you will actually see from your digital thermometer that the bud and blossom temperatures immediately “pop up” (usually to about 38 F ). When water freezes there is a beneficial release of heat (called heat of fusion), and as long as you can keep sprinklers turning you will be able to maintain temperatures of the floral tissues above their critical temperature.
  • In case of serious winds, you will definitely need extra labor to work with you tonight (Tue/Wed), and probably Wed/Thur as well, to knock ice off nozzles – right now we are on the edge of a true windborne freeze in most areas, so there is an excellent chance of nozzles freezing up.
  • In case your pump fails, I  have seen growers come through a situation like this as long as they could get their sprinklers “going again” – you may have up to 1 1/2 – 2 hours to get the irrigation running again — monitor bud and blossom temps with your digital thermometer to know how critical the patient may be?
  • Keep running the water into Sunday morning after sunrise, and do not stop until the blossoms in coldest part of field are above 32 F. You should have at least 5 blossoms set up with thermocouple wires – DO THIS BEFORE SUNSET AND TEST