How to protect young grapes from frost

Grape    Lausanne, Switzerland

About two weeks after bud break, we are scheduled to have a frost (-2C / 28F) in the next few days. I have quite a bit of fruit on my plants and I'm looking to protect it. Any tried and true methods how to do this would be appreciated.

Posted by: deactivated (25 points) deactivated
Posted: May 12, 2013


Not many tried and true methods for non-commercial growers that I know of. For grapes, the traditional method is overhead sprinklers (where the ice freezing on the vines keeps them from being damaged.) Smudge pots aren't very effective, and helicopters (pushing warm upper air down) only work when there's no wind.

Perhaps what may work for non-commercial growers would be what I used three times last year (of which I think one of the times might have been effective)..this was a product called KDL from Agro-K. It's potassium dextro-lac, basically a salt and sugar solution. When sprayed on grapevines 12-24 hours before a frost event, may provide 1-2 degrees extra of cold/frost tolerance for the young developing shoots and buds. Basically what the solution does is become absorbed in the vines and especially the soft tissue, lowering the freezing point. So, whereas normally the frost point might be around 31.5F fo grapes, they can withstand about 30.0F. Every little bit counts.

If all else fails, pacing nervously is another option, as well as prayer. Or replanting your vineyard to a more appropriate site......--Carl

Posted by: Carl Helrich (12 points) Carl Helrich
Posted: May 13, 2013

deactivated commented,
Thanks Carl! Neither prayer nor replanting are options for me, but I'll go with science and try KDL if I can get my hands on it.
about 7 years ago.

One method used to protect frost-tender ornamentals when overnight temperatures get lower than usual here is to string holiday lights on them. The small amount of heat from the tiny bulbs, especially if the whole plant is under row cover, is usually enough to save the plant. It works especially well for plants trellised on the wall of a house, where an electrical outlet is handy.

Cloud Cover is another product that's been used to protect plants, but I don't know if it's ok to use on edibles. It's an antitranspirant and the MSDS says it's ethylene glycol.

I'm a member of a tomato forum, where backyard growers talk about doing all kinds of creative things to protect their plants from cold snaps. Covering with whatever is at hand is the easiest thing to do, but you want to make sure that the cover is not touching the plant, because the layer of air between plant and cover provides some insulation. Do you have trellis material or fencing or wire cages you can prop up next to the plants as frames for a cover? The covering can be anything -- old blankets, cardboard boxes, sheets of plastic, etc. -- as an overnight cover, or something that transmits light if you need to cover them for several days and nights. (I use bubble wrap around my tomato cages until late May.) Some tomato growers cover their plants and burn candles inside to add some heat, but the structure needs to be fairly stable and not flammable!

Posted by: Tanya in the Garden (128 points) Tanya in the Garden
Posted: May 13, 2013

I hope it is not too late, but covering vines with a frost blanket works as long as the blanket does not touch the grape leaves. It is all about heat to prevent frost. Grapes can take down to 30F depending on variety. Use of sprinklers only work if you put out enough water which is about 50 gpm per acre. This a sprinkler that sprays 5 gpm in a 360 pattern every 1min. the trick with water is to start before the temperature gets to the critical 30F. This depends on wet bulb and dewpoint, but a good suggestion is to start at 33F and don't turn it off till 35F the next morning when the ice is melting on its own.

A few vines should be protected with blankets, or heaters. Heaters work great and have been used for 1000s of years by man. The trick is enough heat, you need 4-6 million btu's hour per acre. And remember more small fires is better than a few big fires. Also heaters are the only thing that works if the wind is blowing, sprinklers will not work and in fact kill plants if the wind is more than 3mph. To give an example for heat, that is about 50 gallon of fuel oil per hour per acre, and about 1000 lbs of dry hardwood per hour.

Posted by: David Lawson (5 points) David Lawson
Posted: May 13, 2013

I'm posting some results here. As you can see in the first image, I covered one row of very young / small grapes in cardboard boxes. The second row was covered in blankets (with some cardboard at the top where the blankets were attached).

The grapes in the cardboard boxed suffered substantial damage, but it's most likely due to the fact that parts of the plants actually touched the cardboard box.

The grapes in the blankets showed no damage whatsoever. I was extra careful in ensuring that the plants did not touch the blankets.

The temperature was -1C / 30 F

Posted by: deactivated (25 points) deactivated
Posted: May 15, 2013

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