4 replies to this topic

[h20manblue]

Got nailed with frost/freeze during a super cold three day stretch Mid April...buds were pushing and about 1/3 to 1/2 of them got fried.
They started a nice come back only to awake this morning to surprise frost on the roof of the car...definite scrapeable frost, and a quick inspection of the vines seems to indicate a strong possibility of bits of frost there. :/
My thermometer only shows 39 as a low from last night. Time to check the inner workings of the thermometer....unless I'm wrong and frost is possible at 39 F?

[Grafted Grapevine]

If your thermometer is under some sort of a roof or overhang, it could show air temp, but not give the impact of radiation frost. By this, i mean a condition where the thermometer (or grape leaf/shoot) is insulated from ground heat radiation, like grass/ground cover, the sky is totally clear of clouds, and it is wind still. The clear night sky will allow the heat to radiate freely out into space, and the still air will prevent the surounding air from replacing the heat. This causes frost to form on car hoods, on the grass, and is commonly seen on the tops of vineyard canopies. The good news is that if you have enough humidity in the air, the formation of frost (freezing of the water in the air) actually releases energy from the water in the air as it freezes (thats how irrigation works to protect against frost damage). That frost formation helps to keep your tissue temp of your shoots and leaves near 32. It needs to get down to 28 to injure the tissue. So it is very likely that you didn't exprerience any injury last night.

[h20manblue]

Thanks for the quick reply...I'm thankful that after another inspection with the sun up, it looks better. I think you are right that tissues survived.
Still, it was mighty cold for May 12 here....really strange year.

[DesertDance]

I hope your vines survive too! We are blessed with a lack of frost and snow. Sometimes the golf course (in what we call winter), has frost delays. This is rare, and has never affected the vines. Only once in 8 years has the frost killed the bougainvillas. Vines just truck right on! Good luck this year with your vines!

[ace10]

Depending on your exact location, your frost free date is likely closer to 24MAY.

http://davesgarden.com/guides/freeze-frost-dates/index.php?q=01201&submit=Go