I have some experience, most of it bad until I built a greenhouse. There are numerous problems trying to cover individual trees. It takes a huge amount of material both for the frame and the covering material. Without heat it isn't very effective. You can cook the fruit if they are covered with poly and the sun comes out. It's very labor intensive. Our weathermen aren't very effective on giving us warning. I had a frame and rug over a small peach last night. It was supposed to drop to 34F but dropped to 23F last night and hasn't been above 30F all day.

With my greenhouse, 1700 sq ft, I've had no frost or weather damage in six years. Few pests and a huge harvest. Outside on a bigger area, nearly nothing.

Where do you live and how bad are your frost problems? Do you have a lot of wind along with the cold? These are necessary to know your best solution.

Thanks for your reply fruitnut.

I live in Northern California, about two hours north from Santa Rosa. THe winds don't normally coincide with the frosts and the location is on a hillside with an altitude of 1300 feet, which seems to reduce the frosts. We have probably had a maximum of 3 frosts this winter (all before January) but I'm sure we'll get at least one night of below 32F temperatures.

Some people talk about wrapping christmas lights around the trees. Does that actually do anything?
What about the cold-resistance sprays?

Yeah, I wish we could afford building a big green house but we don't.

Anyways, thanks for your help so far.

Xmas tree lights can help a little. You might try that in combination with some frost blanket over the top of the tree. I'd get the heavy duty frost blanket such as Agribon. Cover the top of the tree and part way down the sides sort of like a hair net. Tie it on with some twine. You can leave it on until frost danger is past. You might want to prune the top of the tree to even things up. It shouldn't damage the tree resting right on the branches.

It also helps if the ground is bare, firm, and wet. This maximizes heat transfer from the ground into the canopy.

The frost blanket won't work here because of our high winds. But in CA you don't have as much problem. I'd try it out there. And it would be fairly economical since no framework needed.

Good luck.

The advice given by fruitnut is the standard advisement. It is only meant to increase the temp of the canopy by a mere few degrees (I've read up to max +7F if use all 3 of the above) before sunrise -- but where the frost blanket touches the foliage will freeze. You could buy a cheaper frost blanket and triple fold it. The outer layer will provide a little more protection from freezing to the inner layers, but once it's wet and a real freeze comes, the entire thing will turn solid.

Fruitnut: you didn't answer him about the sprays ;-) That, I have no idea whether is beneficial at all or not.

Recently Chris Doll mentioned cold resistant sprays in the Illinois fruit newsletter. Chris Doll is a retired extension fruit specialist and well respected in his field.

He sez:

"Some discussion of cryoprotectant products for freeze/frost protection of fruit crops on the "applecrop" news group began recently, with the mention of a new product being touted. Having tried three different products without any success during my career makes me skeptical about their effectiveness. I will admit, a freeze prediction when trees are in bloom makes such a product rather appealing."

I've tried one anti-freeze product and was disappointed.

Here is a link that might be useful: Illinios Fruit and Vegetable News

Thanks a lot for all who answered. Much appreciated.

About Spray Systems.
***It sounds easy if you say it fast.***

I have over two and a half decades experience
in chemical process R&D and production. The
low flows used here will be enormously unreliable,
expensive, and time consuming. Especially if used
only occasionally in emergency sub-freezing remote
conditions.

***Cheapo Frames and Cover for Mid Size Citrus:

Frames:
I once made frames by using 8 ft T-posts (the
kind used for fencing) driven into the ground
along each side of my citrus row in pairs.

Then I took 1/2"x 20 ft rebar bent in a U where
the bottom part of the U was about as wide as my
pick-up bed so I could haul them home.

The U's were inverted and the parallel parts
were attached to the T-posts with tie wire.

Bottom ends of the inverted U rebars were crotch
to chest high.

The corrugations on the rebar were wrapped in
duct tape to reduce abrasion of the the frost
blanket cover I put over it.

Cover:
Cover was made from 15 oz frost blanket material.
Material was 17 ft wide and 25 ft long. Several
pieces with long edges overlaped 3" & spliced
with duct tape. Use 1x2x 12ft boards or bamboo
poles to lift the cover. Weight the cover with
concrete blocks.

Heat:
Heat was supplied with 30 gal garbage cans set be-
tween the trees and filled with water.
This works because citrus can take several deg below
32 deg. and the water gives off 80 cal of heat per
gram as it freezes.

***Problems encountered:

Tape holds really good only if dry. Sew it.
or find some fastener.

1/2" smooth bar will be easier to get the cover
over but hell to tie to the posts.

Something besides duct tape on the rebar is needed.
for long term use.

***Emergency only.
Not inended to be a greenhouse it got my 2-1/2 yr
old trees thru a short cold spell to 19 deg after
they were actively growing in March 2002.
Trees were to 9-1/2 ft tall. Only a few tips died.

If you're not in a hi-number zone, do like Fruitnut.

Greenmonk:
I'm sorry about bringing up water spray. I misread.

That used be the rage for citrus in Florida. On
a large scale, it may be cost effective. On a small
scale it is not.

I'm still miffed about someone wanting me to put
one in for thirty trees. And run it. And that
was six years ago.

I have however, kicked up the pressure on a drip
system and flooded the orchard. That is about as
effective as a lot of things if the trees can
stand it short term. This works on an adiabatic
freeze only and only if the trees aren't real tall.
Again we were protecting citrus and young Mexican
avacados down to 19 deg.

I've always believed that if you can spray down the tree before the sun rises that you can prevent frost damage. I had a small orchard a few years ago, about 40, and I did this a couple of time and seemed to work. I think that the sun actually causes the damage by rapid evaporation or something like that.?? My new peach trees will get the same treatment if it frosts while they are in bloom. It's the only thing that I know to do. Keeping my fingers crossed.

Luke

I once put a heat lamp in a peach tree, covered the whole tree with plastic, wound up with an 18" circle of peaches from where the lamp hung to the top of tree that summer.

A few degrees off-topic, but losing fruit to freezes is one of those most discouraging experiences, and the only real answer is to not plant your orchard in a late-frost region. I wish the USDA had maps to show this, as the hardiness zones in nursery catalogs are pretty useless to tell what will reliably fruit in your location.

Pick your battles more carefully and put in a different and tougher fruit tree. That probably means something other than stone fruit.

The watering down of the trees before sun rise sounds like an intriguing alternative to me since it'd be very cost-effective if it works. The temperatures hardly ever drop below 30F here, but I think I lost my crops to a late frost last year. Does it matter if the sprayed water is cold (since we have our own well)?

I think another issue I have is that the trees are planted on a narrow strip that has a high dirt bank right behind the trees and they face south, so the spot heats up possibly too much in early spring and the trees blossom too early. Could this be part of the problem?

greenmonk:

Spraying the trees before sunrise will do nothing to save your fruit from frost. If it does anything it will cool the tree slightly by evaporative cooling. If that worked all the commercial growers in frost prone areas would be doing it and they don't.

Your microclimate could cause the trees to bloom a few days to a week early. Not really much in your climate. If you seldom drop below 30F you don't have much to worry about. I've seldom had losses unless it drops below 30F. Frost may not be what happened last year.

My winters are as warm as yours. We bloom just about as early or nearly so. We were 20F last week and 18F this week. We have many frosts yet to go.

In an adiabatic freeze there is no wind and it typically happens when those high pressure domes are directly overhead.
The temperature dips sharply right before sunrise.

The objects are cooled by radiating to the sky and are colder than the surrounding air. No conduction
or convection. Its like a loophole in the second law of thermodynamics. It is why you can get frost at 38 deg F.
Most of our freezes are of this type.

Many people here use large spray nozzles to save expensive ornamentals when temps are slightly below freezing. Evaporative cooling occurs if there is wind.

The process rapidly becomes impractical on a large scale due to the volumes and piping and the swamp it produces.

To get around some of this citrus growers in Florida have used micro nozzles to spray small trees since they freeze much worse than mature ones. These guys have huge budgets and lots of manpower to pull this off.

This is described in Citrus Industry Magazine which I receive.

looking to grow goji berries.

do i need frost protection?

Here is a link that might be useful: goji berries

Under which conditions might frost burn while overnight temps are in mid 30's? If so, how does one detect these conditions? I've just started to try smudge pots but need to know when to light them. We live at 2500 ft elevation.