Some information on cold protection...

floridays(9B)January 4, 2010

Here is an article I wrote for a presentation at a Rare Fruit Council meeting. It is a summary based on experiences of members as well as myself...I hope it helps (though a bit late!)

Cold protection of tropical fruit trees in the Florida landscape for homeowners

Scott Walker


Hurricanes, droughts and pests are among the biggest problems affecting tropical fruit growers in Florida, but one of the most problematic factors in Florida is a freeze.

Since the turn of the century, citrus growers have used various methods to protect crops from impending freezes including the use of smudge pots, tenting and flooding. The original Temple orange tree was saved from a destructive freeze in 1917 when its owner, Louis Hakes, stayed up all night "babysitting" the treasured tree. He used a kerosene heater and a large tent over the tree, in which he camped out on a cot through the night. Talk about dedication.

In 1989 Florida suffered a major freeze when temperatures fell into the teens in Central Florida and lower 30s in even the southernmost areas of the state. This event destroyed many citrus groves as well as tropical fruit trees - both commercial and residential. Even over the past few years there have been drops in temperature during the winter months which prompted many to take protective measures to preserve their crops and trees.

Types of freezes

Freezes can be classified as either radiational or advective. A radiational freeze occurs when a cold air mass settles into an area. During this type of freeze, there is little to no wind and cloud cover is absent. However when cloud cover is present, it acts as a greenhouse effect, trapping in ground heat as it is released throughout the night. Some wind can also be beneficial, as it does not allow cold air to settle in any one area.

Advective freezes are characterized by windy conditions accompanied by a large dry air mass rapidly moving into an area. This creates a sudden and rapid drop in temperature and makes it difficult to protect sensitive plants. Wind breaks may help in this situation, but saving the trunk and graft union may be the best focus of attention.

The Basics of cold protection

One of the primary methods of protecting fruit trees from cold weather is location of planting. The south and southeast sides of a home are typically the most warm, absorbing heat from the sun throughout the day and releasing some of that heat during the night. Many growers water the ground copiously the day prior to a freeze as the wet ground absorbs more heat from the sun and slowly releases it throughout the night. This in combination with covering a small tree can be enough to prevent damage to a tree that would otherwise suffer. Another method is covering small trees to prevent heat loss and frost. Some of the materials used for covering are burlap, sheets, frostcloth or blankets. Plastic is not recommended unless a frame is built around the tree so the plastic is not touching the plant, as this can lead to foliar damage.

An additional factor in determining survival in trees is the health of the tree itself. A well nourished tree will cope with stress and cold far better than an unhealthy tree. A regular nutrition program consisting of either organic or chemical fertilizer will bring the tree into the winter months with an advantage. It is important however to end feeding by October to prevent growth flushes which would be susceptible to cold weather.

Even colder

For more severe freezes a combination of covering and lights can be used. The standard C-7 or C-9 Christmas lights offer a great source of heat that does not harm the plants or create a fire hazard when used according to label instructions. Others methods of heat are standard light bulbs and portable flood lights. It is important when using a high wattage electrical heat source, such as a flood lamp, that all precautions are used according to labels and directions so as not to cause a fire.

When trees become so large that covering is no longer practical, lights may be used in combination with wrapping the trunk and major structural branches with blankets or cardboard. Using this method, even if foliage or small limbs are damaged, the tree itself should recover.

After the Freeze

The morning after a freeze, when the temperature rises above 32 degrees, plants should be uncovered. Initial damage may not be visible and may not show for a few weeks. One reason to refrain from pruning is that some branches may look damaged but will actually recover. In addition, pruning may initiate a premature growth flush that could be damaged by another cold event. Transpiration (water loss through the leaves) is a problem that can occur on a sunny day after a freeze. Plants should be monitored for water needs and water may be applied to both thaw the soil and provide moisture.

Other options

If the threat of cold is a factor due to location (i.e., living in a cold pocket or in the northernmost parts of the state), subtropical fruits are good alternate choices. Fruits such as blueberries, jujubes, pomegranates, Oriental persimmons and white sapote are excellent hardy additions to a landscape. There are also cultivars of avocado such as Brogdon, Lula, Gainesville, Winter Mexican and Choquette that will survive temperatures from the low to mid 20Âs.


· Two types of freezes - Advective and Radiational

· Planting location  South side of house is best

· Nourish trees in early Fall

· Soak the ground (under the trees) with water the day prior to a predicted freeze

· Cover plants /trees with  frostcloth, burlap, sheets or blankets. Large cardboard boxes (refrigerator) can also be used for smaller trees

· Wrap trunk (from branching to ground level) with blankets or other material for extra protection

· On coldest nights Christmas lights (C-9 or C-7) add heat

· After freeze - Remove covers, watch for desiccation and hold off on pruning

· In a consistently cold area consider subtropical fruit trees

Cold Sensitivity of Tropical and Sub Tropical fruits in Florida

Fruit Scientific name *Average cold tolerance of adult trees (in Fahrenheit)

Avocado Persea Americana 25-30

Ambarella (Dwarf) Spondias dulcis 28

Atemoya Annona cherimola x squamosa 28

Banana Musa spp. 29

Barbados cherry Malpighia punicifolia 29

Black Sapote Diospyros digyna 29

Blackberry Robus argatus 20

Blackberry jam fruit Randia formosa 29

Blueberry** Vaccinium corymbosum (blossom) 28

Canistel Pouteria campechiana 28

Carambola Averrhoa carambola 28

Ceriman Monstera deliciosa 31

Cherry of the Rio Grande Eugenia aggregata 25

Fig** Ficus carica 15

Green Sapote Pouteria viridis 27

Grumichama Eugenia braziliensis 28

Guava Psidium guajava 27

Jaboticaba Myrciaria cauliflora 26

Jackfruit Artocarpus heterophyllus 29

Jujube** Ziziphus jujuba 26

Longan Nephelium longana 26

Loquat** Eriobotrya japonica 22

Lychee Litchi chinensis 28

Mamey Sapote Poiteria sapota 29

Mango Mangifera indica 28

Miracle fruit Synsepalum dulcificum 29

Mombin Spondias purpurea 28

Papaya Carica papaya 30

Passion fruit Passiflora edulis 30

Peanut butter fruit Bunchosia argenta 30

Persimmon (Oriental)** Diospyros kaki L. 15

Pineapple Ananas comosus 29

Pitaya Hylocereus sp. 28

Pitomba Eugenia luschnathiana 28

Pomegranate** Punica granatum 24

Rollinia Rollinia deliciosa 29

Rose apple Syzygium jambos 27

Sapodilla Manilkara zapota 28

Strawberry tree Muntingia calabura 28

Sugar apple Annona squamosa 28

Tamarind Tamarindus indica 28

White sapote** Casimiroa edulis 25

** Subtropical or Temperate

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puglvr1(9b central FL)

Thank you so much for posting this Scott...very helpful and well written. I'm guessing the temps for the mango and lychee trees posted above are for mature trees? I have some young ones planted 2 1/2 years old do you think they have to be to be able to tolerate 28° for a couple of hours with little or no protection? I was always under the impression that 32° or below can do damage? Thanks again!

    Bookmark   January 4, 2010 at 7:29PM
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I covered everything last night with special fabric I bought from Lucas nursery... It was 31 in my area. Today all papayas look dead frozen....All citrus's new leaves are dead too. I am afraid my young avocado this year will die again like another avocado died last winter. No matter how I cover them they die anyway.

    Bookmark   January 4, 2010 at 7:55PM
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Great post Floridays...thanks for the info. This is a nasty cold snap.

    Bookmark   January 4, 2010 at 8:14PM
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Thanks Puglvr, I had two mangos (two years old) that I left uncovered last year (when we hit 26.7f) and while they had some foliar and branch damage they have since fully recovered. I would however try my best to cover and heat if at all possible. I have seen large trees that have skirted low 30s with only foliar damage.
My theory is sort of an "Extreme Gardening" approach and I like to push zones. This is not for everyone but in my way of thinking it's sort of a challenge. (I also have an assortment of Figs, Persimmons and others that aren't bothered by cold)
Ana, the frostcloth may protect from frost developing but with temps below freezing a combination of lights would be very helpful. Do you remember what variety of Avocado you had? There are some that are much hardier than others such as the Brogdon (and it's self pollinating).
The Papayas can recover, I've seen them pruned back to 2' and have come back as a double stem and have fruited. The citrus growth will all come back, not to worry.

Again, with temps less than than 32f and young trees, heat AND cover is recommended. If there is one thing I have learned is that things will recover (even if only a small bit above the graft line survives) and within a year can make a remarkable recovery.

Bluepalm, thanks! I think I have seen pics of your yard and trees..very nice selection!

    Bookmark   January 4, 2010 at 8:41PM
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wilmington_islander(9A/Sunset 28)

Great info...and mirrors most literature. However, I can tell you from experience that p. edulis " black knight" and "purple possum" can handle 23, with no frost, with no problem.

    Bookmark   January 4, 2010 at 10:42PM
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Even though the plants look as though they have been toasted with a flame thrower - remember - NO pruning for several months .
Do NOT cut at all !
It's very hard to obey this rule . So tempting to remove black foliage .
floridays- can you write a new post on the many reasons why we need to leave our sad winter burned plants alone and wait ?

    Bookmark   January 5, 2010 at 6:40AM
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W Islander, thanks for the information on those two passiflora species I had heard that there is great cold variance between species. Gotta love field experience.

Gatormom, I can't stress enough that pruning should wait until March 15 (and even at that date check the forecast). If nothing else the dead brown ugly branches and leaves may act as a buffer for the live growth. I try and follow the natural regrowth patterns of a tree or plant and this regrowth after freeze damage usually occurs around March.
No pruning!

    Bookmark   January 5, 2010 at 8:09AM
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Thank goodness we received some cloud cover last night...temperatures were almost 5 degrees higher than forecast. All of my plants are covered with the exception of a larger Glenn mango (I am covering it today) and a 10' Kohala longan which will remain uncovered (I am going to put a set of painter's lights under it tonight). I just saw a satellite loop of the weather and the cold front is pushing down here hard and will most likely drive the cloud cover away.
Another idea to generate heat under your frost cloth is to purchase "Super Hot Hands" in the hunting section of Walmart. A 3-pack is $1.99. I bend paper clips into hooks and hang 1-2 of these bags on a lower limb of my covered trees around midnight-1 a.m. when the cold really sets in. I've done this the past 2 years and they seem to generate a good amount of heat. They are especially useful for yards like mine where I have 30+ trees...some at a good distance from my house, so putting Xmas lights on them is not an option for all of my trees.

    Bookmark   January 5, 2010 at 9:10AM
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whgille(FL 9b)


Thank you for posting this very invaluable info on the fruit trees. Just like everybody else, I am too worried about my so prized fruit trees.

But since I went through this the last year, I took some precautions this year. The very sensitive are in pots either in the garage or porch. The other ones I hope they will make it.

Last year I lost a mango and a star fruit, the Brogdon is still alive and so is the atemoya. Papayas I can afford to loose, they are cheap enough from seed and grow fast too.

Good luck to us all after this cold snap!


    Bookmark   January 5, 2010 at 9:28AM
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floridays ---Thanks so much for writing this post. I had looked for my cold protection post from last year but it is missing.

Since I really tend to push the limit on tropical fruits and my location is 9a, I have to use something that really works. I am a big fan of what you call "tenting" with plastic. I make a framework, so to speak, of tall green garden stakes around the tree. Then, I often cover the top of the tree with a sheet and then wrap the whole tree in plastic securing it with twine and clothespins. I have found the 20' x 25' sheets to be the best size for medium sized trees.

As for a heat source, I prefer to use the large bulb Christmas lights. But, I have a 2 acre yard so I have to resort to using hurricane lamps filled with kerosene, one to two lamps per tree.

Here are some pictures taken last year. This is a young Key lime and avocado:

Now, I really took on a challenge by planting a mango. Last year it was a very small tree but with the help of "tenting" with heat, it has grown quite a bit during the year. This picture is from last year:

This is a picture that I took to prove that this method of protection works. The mango flowers are untouched by the freeze. Notice the damage to the banana plants in the background:

Christine --- vice-president of The Tropical Fruit Club

    Bookmark   January 5, 2010 at 9:38AM
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I love the umbrellas holding up the plastic! Very clever and festive too.


    Bookmark   January 5, 2010 at 9:55AM
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Bluepalm, my wife is on her way to Walmart to pick up some "Super hothands"...I have been waiting for a product like this for a long time, the length of heating sounds perfect. I will experiment with them tonight!

Christine, great photos! The mango tenting clearly worked well and the contrast with the bananas is amazing. Great job!
This year I tried a framing method that I learned from Richard Campbell of Fairchild - it is inexpensive and breaks down easily for storage.
Materials used are:
4 10' x 3/4" sections of PVC ($.77 each)
1 Four way connector (cross) 3/4" PVC coupler
4 18" pieces of rebar
4 bolts or cotter pins.

Basically you create a domed frame by assembling each section of PVC pipe into the cross coupler (at this point I drilled small holes through the coupler and the inserted PVC and slid in a small bolt to make sure the PVC didn't pop out of the coupler) and then driving 4 rebar sections into the ground around the tree (vertically). The assembled PVC unit is then bent and inserted onto the 4 rebar pieces creating a dome frame that can then be covered with plastic or cloth.
It sounds more complicated than it really is and if I could figure out how to post pics I would!


    Bookmark   January 5, 2010 at 10:24AM
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love_the_yard(z9A Jax FL)

Scott, that is a fabulous, easy plan. I am going to get the materials to build those. Thank you so much for taking the time to post the instructions.


    Bookmark   January 5, 2010 at 11:19PM
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floridays, I forgot to add: if you are insane enough you can go back out 3-4 hours after hanging the handwarmers, squeeze them (they kind of solidify as the chemical process continues), and shake the contents. This will give you "round 2" of heat. I plan on hanging mine at 11-12 tonight and getting up at 4-5 and reactivating the contents. I'm a sick man for wanting to do this, but these are my prized mangos, longans and lychees people!!!!!! : )
I know you all understand...

    Bookmark   January 6, 2010 at 6:28PM
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Carol, glad you like the plan, it's quick, easy and works well.

All of the "saunas" (PVC frame, light source and cover) I put up around trees were at least 5-7 degrees warmer than surrounding areas, and that's with just bedsheets. I think the agribon is probably warmer, and plastic might even hold in more heat. (next year)

My yard today looks mushy (ornamentals) but the covered 4' Lychees and small Mangos are looking fine. My lowest reading was 23.7 last night and I'm sure we were below freezing at least 12 hours.

This is not pleasant but it is very interesting feedback and good for the journal...ha ha

Bluepalm, I had those handwarmers out all night under a small Fairchild mango, a small Rosigold and a Pink Ohia Lychee and was very surprised that they did not show that much damage. This may be a great thing! I'll try them again tonight and thanks for the re-shaking advice.
When my wife (God bless her) unwrapped the trees this morning at 9:30 they were still warm!

Good luck to all, this by far (barring cloud cover or wind) will be the coldest night yet.


    Bookmark   January 6, 2010 at 9:02PM
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wilmington_islander(9A/Sunset 28)

Thanks Floridays! Most citrus is hardier than expected as orlando tangelo ( loaded with tangelos) just spent consecutive nights with a third on the damage to the fruit leaves, nothing. My key lime has shrugged off 27 ( it is guge)...bur completely defoliated at 26. Go figure. I may have the northernmost in the ground key lime outside of Bermuda!

    Bookmark   January 6, 2010 at 9:46PM
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puglvr1(9b central FL)

Great ideas everyone! Thank you so much for sharing all your valuable information. I just don't how long my trees can survive night after night of such cold(freezing) temps. But I am not giving up w/out a fight...I might lose them them any way...but at least I know I've done all I can to save them.

Scott, would love a photo of your PVC frame or maybe Carol can post one...when you get yours built. Thanks again!

    Bookmark   January 6, 2010 at 10:15PM
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I'll try, I hope it's not too big of a file. This is a frame around a young Rosigold mango.

    Bookmark   January 6, 2010 at 10:42PM
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Here is a pic of the top of the coupler. The bolts are only dropped in, no nuts required. This keeps the PVC from springing out of the coupler.

Additionally, the PVC sections can be cut to match the height of each tree as needed. A full 10' frame can enclose an 8' tree.

    Bookmark   January 6, 2010 at 10:52PM
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love_the_yard(z9A Jax FL)

Very cool! ...I mean hot! Thank you so much for taking the time to post photos.

What did you do with the big blue tub of water? And to be more nosy, what's in the 5-gallon pail (and what did you do with it)?!

    Bookmark   January 6, 2010 at 11:03PM
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OMG! We're moving to zone 9, Sarasota and never dreamed there would be frost that bad that far south. I was planning to bring some of my favorite tropical plants with me and plant them in the ground.

    Bookmark   January 6, 2010 at 11:09PM
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W. Islander, glad to hear your citrus is doing well, I had a key lime lose a lot of leaves one year but recovered nicely. Good luck with that northernmost tree!

Well the buckets are kind of an experiment/advice from an old grower. Basically it takes thermal energy to both heat water and freeze water. I have found that the buckets of water seem to regulate temps inside frames that have no source of heat (in areas of the yard w/out power). Pepper growers have used this method, I think they called it infared heating. Not sure what the results will be with temps this low but it's worth a shot!

greenhouser2, this year seems to be an exception to the norm, especially in an El Nino year that is supposed to suppress these Arctic plunges. Have no fear!

    Bookmark   January 6, 2010 at 11:45PM
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OMG! We're moving to zone 9, Sarasota and never dreamed there would be frost that bad that far south. I was planning to bring some of my favorite tropical plants with me and plant them in the ground.

    Bookmark   January 7, 2010 at 2:17AM
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puglvr1(9b central FL)

THANK YOU Scott! To me, a picture is worth a thousand words. That's a nice uncomplicated, (do-able) tree cover. Thanks again for posting the pictures.

G.houser, I agree Sarasota doesn't usually get this type of weather...its pretty rare. I lived in Bradenton just north,lived there for 12 years and only remember a few nights in that time frame where we had freeze.

    Bookmark   January 7, 2010 at 8:02AM
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Sensitive tropical trees may initially look fine for months after a hard freeze of prolonged duration but
this summer you might see a slow decline and months later bark peeling .
You might attribute it to a disease or insect when the damage is actually from our current freezes .

Last season I lost a Persian Lime , Myers Lemon and Dancy Tangerine this way .
The lime branches and leaves fried immediately but not the trunk; that died later .
The lemon and a few orange trees had peeling bark 6 to 8 months after last year's deep freeze .
This round might just do 'em in for good .

No , I did not protect those trees .
I have protected a young Lee Tangerine year after year and it is still chugging along . Will it make it again ?
Only time will tell - time meaning months and years .
Temper your celebration of survival with the knowledge that trees can show damage long long after the initial injury .

    Bookmark   January 7, 2010 at 8:35AM
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Scott --- Glad to see that you were able to post those pictures. Thanks for posting them. I will make some of those frames for next year. What a clever idea.

The hand warmer packet idea is also good especially since I already have some in my closet that I forgot about.

I thought that I might have the northern most planted Key lime tree. Without protection I know that mine would be dead.

Can't wait for winter to be over!


    Bookmark   January 7, 2010 at 9:31PM
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sharbear50(6a Bella Vista)

Wow what a difference in the mango and bananas. Just for comparison, it would be interesting to cover one banana plant and leave the rest uncovered, just to see the difference in the same type of plant. Will the banana plants recover?

    Bookmark   January 9, 2010 at 3:30PM
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sharbear --- The banana plants don't need to be covered. They recover nicely on their own. The plants have been there for 10 years. I have cold tolerant varieties. Although, I have to say that this cold snap will really put them to the test. We had many nights in the low 20s lately.

This year the mango tree is 8 feet tall and doing well under the plastic with heat for the last week and a half. If tonight is really the last freeze for a while, I get to take the plastic off tomorrow.


    Bookmark   January 12, 2010 at 11:20PM
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puglvr1(9b central FL)

Christine, great news on your Mango tree...that little makeshift greenhouse really worked well for you, congrats!
I really hope this is the last wicked cold spell for the rest of the year. I know its wishful thinking...

    Bookmark   January 13, 2010 at 7:26AM
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I know it's a little late to be commenting on this post that turned up in my search for info on Loquat, Eriobotrya japonica. Although this thread didn't have anything to do with my question about Loquats, I couldn't stop reading.

Scott, you did a great job on this article. I enjoyed reading it and learned a lot.

I'm particularly interested in the cold frames you made with the PVC. Last year I made some out of wood for my mom and stapled plastic to it. I will not do that again.

I have a few questions for you, if you don't mind.

(1) What width or diameter PVC did you use? I didn't realize PVC was that flexible. What makes it hold that shape?

(2) Did you just sink the ends of the PVC directly into the ground? I couldn't tell because of the blankets.

I'd like to be prepared long before winter sets in this winter. Your frames are great because they look easy to construct and easy to dismantle & store when not in use.

Thank you.

    Bookmark   March 17, 2010 at 10:23AM
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I'm glad you found the information interesting. I'm happy to say that in the worst winter I have experienced ever in Vero, all of the trees that were covered and lit using this method are not only alive but blooming and flourishing. It works.

To answer your questions:

1. 3/4" PVC (the cheapest @ $.77 for a 10ft section)

2. The PVC is slid over rebar (2' sections) that are driven into the ground.

They bend easily (and straighten back out easily), and the bending is just from the tension of one end in the 4way connector and the other in the rebar base.

Hope this helps!


    Bookmark   March 17, 2010 at 2:38PM
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Thanks for the great article and list of fruit trees! That settles it; I'm gonna wave to find a white sapote, cherry of the rio grande, jaboticaba and longan. Here in Jax (9a) a neighbor of my coworker has had a lychee tree for years and its apparently still ok!

    Bookmark   March 17, 2010 at 8:19PM
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Scott, thank you so much, this is very helpful. ingenious!

I'm so glad to hear that all of your trees that were protected by this method are blooming and thriving. It sure makes it worth the effort when they survive.

Great job!

    Bookmark   March 18, 2010 at 7:20AM
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gfc56(z8 Fl)

I was wondering if a spa solar cover like this one over a cold frame would provide a good barrier against the cold. Possibly even a emergency thermal blanket.

    Bookmark   June 23, 2010 at 6:51AM
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