Great Tip on Using a Second Row Cover! (4:02pm, Mon., 3/13/17)

— Written By
From Eric Hunter, Easley, SC
I just talked with Peter at AgroFabric and he did a good job of explaining the capabilities of using double covers. He said that two covers do a great job of holding in the heat, but a poor job of allowing the sunlight to penetrate through and actually heat the air and ground under the covers. He said that anyone choosing to do double covers, should apply that second cover during the afternoon of the expected event so that the sunlight will have an opportunity to heat underneath the first layer. This makes a lot of sense, and it explains something that happened to us several years ago during a single digit episode where we used double covers. The first night of the cold event, our covers gave us almost 15 degrees of protection, but the second night it was much less. 
Our saving grace right now is Skybit – it has us dropping to 22 on our coldest night – however, one thing I’ve learned is that Skybit is famous for falling in line to hit the actual low the day before or day of the event. I think once we get to tomorrow, I’ll have a much clearer picture. 
Tomorrow and tomorrow night is supposed to be very windy with gusts over 20mph (even during the night). We will be around the 20-22 degree mark I believe. If the forecasts other than Skybit (AWIS,NOAA) hold true and it appears we will fall into the teens for Wednesday night, my plans will be to remove the second level of covers on Wednesday morning, and then reapply them that afternoon to maximize heating.
One other thing that growers who use sprinkling on covers should be aware of is what happened to us. The last time we attempted to use this method, we didn’t have to turn the water on until the air temperature was at 26 (we were using the thermocouple inside the bud to guide us). By the time it was time to turn the sprinklers on, all of the ball valves and all of the risers that the sprinkler heads were connected to had all frozen solid due to already being exposed for a few hours to below freezing conditions. It would be wise to drain the lines of all water ahead of time to make sure this doesn’t occur.
Thanks!
Eric Hunter
No, THANK YOU!! Excellent tip to pass on to other growers! Also, if any growers have recently purchased a new digital thermometer, please send me the updated pricing. Also, I wish to say that I just did an on-the-fly revision of the leaflet I just sent out on using a digital thermometer, and some of you may have caught this edit…
 

Before it read:When to start irrigation in a freeze?

 If you use only sprinkler irrigation for cold protection, be sure to start irrigating as soon as the digital thermometer indicates the blossom temperature is 31/32 F. The air temperature may still be as high as 38 F if the air is dry.

If you combine irrigation and row covers, we suggest starting irrigation on top of the covers as soon as blossom temperatures beneath the covers fall to 28 F.

Now it reads:  (taking into account the problem Eric mentions with sprinklers freeezing up)

When to start irrigation in a freeze?

 If you use only sprinkler irrigation for cold protection, be sure to start irrigating as soon as the digital thermometer indicates the blossom temperature is 31/32 F. The air temperature may still be as high as 38 F if the air is dry.

If you combine irrigation and row covers, we suggest starting irrigation on top of the covers as soon as blossom temperatures beneath the covers fall to 31F.

Also, I’d like to point out that one of the real advantages of using a row cover in conjunction with sprinkling, and not trying sprinkling alone on frost/freeze type night (note, sprinkling alone should never be attempted in sub-freezing conditions with windborne freeze of 8+ mph), is that if your irrigation system freezes up, or breaksdown, the row cover gives you a very nice grace period of maybe an hour or more, to get things running again…

I just received this note a minute ago from a grower friend who has been doing a truly spectacular job over these last 2 weeks with using sprinkling alone, but this is what happened today:

“Spent the last two weeks babysitting blooms. 7 nights sleeping in my truck. Had to run OHIRR 3 of those nights. Last night fired up for frost protection and blew a hyd seal on tractor. Heavy frost by the time I switched tractors. 2 weeks worth of work down the tubes.”

Written By

Photo of Dr. Barclay PolingDr. Barclay PolingFormer Professor and Extension Specialist, Strawberries and Muscadines (919) 515-5373 (Office) barclay_poling@ncsu.eduHorticultural Science - NC State University
Updated on Mar 13, 2017
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