Florida Got Frosted! (January 2018)

You don’t often see icicles hanging off a papaya plant. A farmer near Gainesville turned on misters spraying water in his greenhouse overnight as a heat source to protect the potted papayas and other plants. The night got colder than he anticipated, and temperatures in parts of the greenhouse dipped low enough to freeze both the sprayed water and some of the potted papayas, encasing some in ice. Fortunately, parts of the greenhouse didn’t get as cold, so not all his papaya stock, intended for spring planting, was lost. (Believe it or not, this papaya plant actually survived – details in an upcoming post.)

Every winter we get our our annual reminder that North Florida is not actually tropical. Usually a number of cold fronts interrupt our mostly warm warm weather with a dose of north-temperate zone reality, bringing us a series of chilly days, and nights dipping below freezing. The latest such cold wave was January 3rd through 7th, 2018.

Despite what some in in the news media were saying about “record cold” in Florida, this latest stretch of several days of frosty weather was a completely typical of what happens in winter here. In my area (between Ocala and Gainesville), the temp briefly dipped down to about 25F(-4C), which is right about our average extreme winter low. During really nasty winters, I’ve seen the temperature drop as low as 15F (-9c) here, so this week was not bad at all. Sub-freezing temperatures penetrated down into the middle of the peninsula, with the Orlando and Lake Wales areas reaching about 30 F ( -1C), and coastal Sarasota stayed just above the freezing point.  While these temperatures are lower than those areas got during the previous couple of extremely mild winters, they are pretty much exactly in line with the long-term average extreme lows for the region.

But since even a mild episode of sub-freezing temperatures has a profound impact on what plants can grow here, I figured I’d give a roundup of what happened in the latest cold snap in my area of north-central Florida , and how methods I and some other growers employed worked or didn’t work.

These ‘Sunburst’ tangerines came through the freeze fine, and are now getting sweeter every day. Most citrus varieties carry fruit through at least part of the winter. For ‘Sunburst’, I’ve found it’s got to get down to at least 20F (-7C) to damage either trees or fruit.

First, the fruit trees that normally handle frost sailed through this freeze fine: citrus, figs, cold-hardy avocados, mulberries, olives, persimmons, grapes, plums, pears, blueberries, and loquats – all had zero damage that I can see. It helped that this freeze came in early January, right when all these trees are at maximum winter dormancy, which helps them handle cold weather.

During some years, we get weeks of warm weather in January and February, causing some fruit trees to wake from dormancy, pushing out tender new growth. If a hard freeze then hits in late February or early March, it can cause them catastrophic damage damage to these actively growing trees. But in this latest freeze, we had some cool weather leading up to the cold snap, and the cold happened in early January, so this was a textbook example of a “good freeze”.

Even though the tangerine fruits came through totally undamaged by the cold, unfortunately my trees have a very small crop of tangerines this year. At least part of that is due to the spring drought we had – citrus trees here flower in March, and the fruits steadily develop for the rest of spring, summer, and fall, ripening in winter. An intense spring drought can make the trees drop those developing fruits, and that definitely happened this past year.

On a frosty winter night, these papaya plant babes are snug in their warm beds, dreaming tropical dreams. We wrapped Christmas lights wrapped around them as a heat source, and covered with a layer of frost cloth and plastic. They survived the freeze successfully, while papaya plants given lesser protection froze.

Papaya plants really thrive in the heat and humidity of our Florida summers, and can produce tremendous amounts of food. But the plants are quite cold-sensitive, and can easily get killed by single freezing night, so it’s worth a bit of effort to get these tropical plants through our winter cold spells.

We successfully protected a planting of young, 3-6 foot (1-2m) papayas in this way: first we wrapped Christmas lights around the papaya plants as a heat source, one 40-watt string of lights per plant. Then we put in a ‘T’ of PVC next to each plant as a support, and covered the plants with a layer of frost cloth, then a layer of clear plastic. This method worked beautifully to protect the plants. If we can get these papayas through the rest of the winter, they should reward us with bountiful production of fruit next summer and fall.

I tried giving some other papaya plants lighter protection, just draping sheets and blankets over them. This method works to protect plants in milder freezes, but in this case the papayas protected this way received substantial cold damage, and may have frozen down to the ground. (Not a major setback, as I’ve got potted papayas ready to plant out in spring.)

Laying cold-sensitive potted plants on their sides and covering with layers of plastic and frost cloth works beautifully for protecting them from cold. Shown here fully covered, and when I first pulled the covers back after the freeze – still green!

Potted plants are easier to protect than plants that are growing in the ground, using a simple technique: just lay the potted plants flat on the ground, and cover them with sheets of cloth and plastic. The warm earth produces heat, and the sheets trap it around the plants.

During this latest freeze, I used this method successfully in my nursery to protect potted tropical plants. Prior to the freeze, I had grouped all the cold-sensitive plants together. When the forecast showed sub-freezing weather was about to arrive, I laid all these plants all on their sides, piling them on top of one another, and covered them with a big sheet of plastic, then an old sheet of frost cloth on top (frost cloth is available from nursery suppliers.) I used no heat source other than the ground itself. I left them covered like that for the few days of the freeze, then when things warmed up I pulled the covers off and stood the plants back up. Everything was fine.

This method is labor-intensive and messy, with lots of spilled soil, and it can be kind of visually unattractive. If you only have a few plants, this is quick and easy. If you have a whole nursery full of plants, as I do, it’s a time-consuming pain in the butt, both to set up, and to take down after the freeze. But it works really, really well.

These small tropical fruit trees survived the freeze with no damage, because they were planted in the shade of big evergreen oak trees. Chocolate pudding fruit (aka black sapote, Diospyros digyna) on the left; mango (Mangifera indica) on the right. Had they been planted in the open, they probably would have been killed to the ground. Update: We got hit by a second freeze on Jan 17-19,  which was slightly colder; the temp dropped to about 24F (-4.5C). The black sapote shown in this pic appears to have frozen to the ground, but the seedling mangos, including the one shown, remain undamaged as of early Feb 2018.  

Another method I’ve been experimenting with is to simply plant tropical plants under the canopy of evergreen trees, especially our ubiquitous evergreen oaks. It’s quite remarkable how much protection that these trees can give to smaller plants underneath them. I’ve been very impressed seeing the results other Florida growers are having with this method, getting tropical fruit trees to survive winter far north of where they are “supposed” to grow. There is, of course, a catch-22 to this method: plants need sun to make fruit, so trees shaded by a heavy canopy will make much less fruit than ones in full sun. But in a region where the same fruit species would freeze out in the open, this may be a way to get more cold-sensitive species to make a few fruits, at least occasionally.

I’ve been employing this method in a super-simple way: when I eat mango, jackfruit, and non-cold-hardy strains of avocado, I walk out into areas shaded by oaks, and push the seeds into the ground. So now there are lots of little fruit tree seedlings sprouting up under the oaks. I also planted a seedling chocolate pudding fruit (aka black sapote) in a shaded spot. Surprisingly, it’s now come through a full winter (last year) and some of this winter, so far without apparent damage. I don’t know if these tree-canopy-protected tropical trees will ever make fruit – if we get a series of mild winters, it’s possible. But I’m a fruit-tree geek, so for me just out of knowing I’ve got a few little mango and chocolate-pudding fruit trees growing in the ground gives me a warm glow.

My tropical fruit greenhouse currently features a greenhouse-within-a-greenhouse. Trees that can handle a touch of frost are in the outer greenhouse; more cold-sensitive species are in the inner structure. All covers come off for the summer.

The way I protect my most important tropical fruit trees is by growing them planted in the ground inside a greenhouse. That way, I can protect a bunch of plants all in one place (instead of running all over the property the day before a freeze, throwing covers over scattered tropicals – which is what I’ve done in the past). Also, in the greenhouse environment, trees can  get big enough to actually produce significant amounts of fruit.

The greenhouse is a pretty simple affair: a standard metal hoop-house, covered with UV-stabilized polyethylene. I take the plastic off for the summer, both to protect the plastic from the summer sun, and to allow the trees to get the full benefit of Florida summer sun and wind and rain. When I have to use something fossil-fuel-based like plastic, I try to get the absolute maximum use out of it I can. In the case of this greenhouse, I’ve been using the same sheet of plastic over the roof since 2006.

The last few years, I’ve been experimenting with setting up smaller greenhouse within the larger greenhouse, for protecting fruit trees that are especially cold-sensitive, or trees which develop fruit over winter, which could be impaired by exposure to near-freezing temperatures. Some of the trees in the outer greenhouse are carambola, jackfruit, casimiroa (aka white sapote), sabara jaboticaba, red jaboticaba, Australian beach cherry, and miracle fruit. In the inner greenhouse are canistel, sapodilla, and pineapple.

To keep the greenhouse warm during freezes, I rely on a combination of extra insulation, thermal mass, and active heating. Commercial nursery frost cloth comes in big rolls – I’ve found I can cut it into a series of strips, which go over the top of the greenhouse, overlapping each other slightly. It’s easy to scrunch them together in the morning to let the sun in, and then pull them back out at night.

For thermal mass, I keep a number of barrels of water in the greenhouse, so they can pick up solar heat during the day, and release it all night. It’s kind of a varied assortment of containers, pretty much anything that will hold water, including a number of plastic trash cans that I’ve painted black to absorb solar heat.

The heating system for my tropical fruit greenhouse is a wood-fired hot tub. During freezing weather, it is absolutely luxurious to soak in the steaming hot water, gazing at the tropical fruit trees all around, knowing that water is protecting the fruit trees from the cold. (That’s a jackfruit tree behind me.)

For active heating, I used to use a wood stove in the greenhouse. That provided quite a bit of heat while the wood was burning, but I found that even using large diameter wood pieces, the wood burned down to nothing in just three or four hours, allowing the greenhouse temperature to plunge during the cold early morning hours. So keeping the greenhouse warm on a freezing night meant getting up several times during the night to stoke the fire. Not good. What I’ve switched to the last few years is a wood-fired hot tub in the greenhouse. That way, I can heat the water up the night of the freeze, have a nice soak in the hot water while the cold winds blow outside, and then go to bed, knowing the hot water is at work, releasing its heat to the greenhouse all night. I can tell you, it is absolutely luxurious to be soaking in steaming hot water, surrounded by tropical fruit trees, on a cold winter night.

For really extreme cold, I can just keep stoking the fire to get the water all the way to approaching the boiling point, and I can stoke the fire under the tub with big fat chunks of wood before bed. That way, even though I know the wood itself will burn out in a few hours,  the heat from that wood will outlast the fire, steadily releasing heat from the water.

After this last freeze, it became apparent there was a small amount of cold-damage foliage burn to the tops of the jackfruit and carambola trees in the outer greenhouse. It’s nothing major, but it does show my heating system could use some improvement. There are a few ways I could do temperature management better than I did this time.  During this freeze, I only had two barrels of water in the greenhouse as thermal mass, with a total of less than 100 gallons (400 liters) of water, while in the past I’ve used many more.  Also, the frost cloth I used this year was a thin grade, compared to a thicker type I’ve used in the past. And I didn’t cover the end walls of the greenhouse with frost cloth, which I’ve done in the past.   I suspect that with better, more complete insulation,  much more thermal mass, along with my existing hot tub heating system,  the greenhouse could come through an even colder freeze than we just received, with little or no damage to frost-sensitive fruit trees.

#freeze #coldprotection #papaya #greenhouse #hottub #winter

Update: We got hit by a second freeze on Jan 17-19,  which was slightly colder; the temp dropped to about 24F (-4.5C). The black sapote shown in the pic above appears to have frozen to the ground, but the seedling mangos, including the one shown, remain undamaged as of early Feb 2018. Some of the papaya plants protected with covers and Christmas lights as shown in the photo appear to have had damage to their central growing point, but others appear to have suffered only external damage and their growing point appears undamaged. See comment below for a report from Marabou Thomas on effects of the freeze on his plantings of tropical fruits in Orlando. 


23 thoughts on “Florida Got Frosted! (January 2018)

  1. Awesome Craig! The greenhouse story reminds me of the years at Koinonia when we grew basil for market through the winter….and basil doesn’t like it below 50, much less freezing. I put two big wood stoves in that greenhouse and on a cold night someone, frequently me, would sleep with the basil! In a thin sleeping bag, so that when the cold woke me up, I knew it was time to feed the fire! Ugh! Those were the days!

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    1. Hi Alder, thanks for commenting. Holy moly, keeping a cold-sensitive plant like basil happy through the winter in Georgia, now THAT is an impressive achievement! It’s just blowing my mind just thinking about it, such an amazing accomplishment. Achieved at significant personal sacrifice!

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  2. Great ideas here, I am in waldo and used a small heater inside my shed with some potted tropical plants, my shed is small so the cost wasnt so bad and my guava and mango did ok. i was wondering about the canopy idea and might use this tip when planting my guava this year, it seemed to do fine on the pot at partial shade this year, so i dont think it will mind the upper canopy pine trees.

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    1. Thanks for commenting! Great to hear you’re growing potted tropical fruit trees in Waldo. Yeah, that planting under evergreen canopy idea sure is intriguing. I’m sure if we got a really nasty winter, stuff would still freeze, but maybe that would happen infrequently enough that things would still get a chance to make some fruits. This past spring, I visited Charles Novak and Pete Kanaris, fruit growers in Tampa, and I was amazed at what they were getting away with in Tampa with this technique – they had canistel and cacao and mango and black sapote trees, getting sizable and in some cases fruiting, under live oaks. We probably couldn’t do cacao here that way, but guava seems possible.

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      1. Hey there, I’m trying to get in contact with Charles for some Illicum verum seeds. Any way you could pass on his email address or some contact information? 🙂 I am going to FGCU for Biology, double minoring in Chemistry and Physics — plan on studying plants used for spices and medicine. I’d really like to get some plants going in our food forest. Thank you so much!

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        1. Hi Aaron, that FGCU food forest is quite impressive. Erica Klopf gave me a tour of it when it was only a little over a year old, and it was really neat already. I’m sure it’s ten times as impressive now. Charles Novak is definitely someone to be in contact with, his collection is amazing. I’ll get his contact info and send to your email.

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        2. Thanks for the swift response!! I actually have an import permit for Dipteryx odorata, and any Piper sp. from several different countries. In fact, I have some real long pepper (Piper longum) coming soon from a nursery in India and I’m hoping I can propagate it and introduce it into the community here in FL! I also have a mutated Banisteriopsis caapi vine with triplets instead of two leaves each node. Really cool stuff happening. :))

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        3. Wow! Are you in contact with Josh Jamison, at the Heart Institute in Lake Wales? If not, I’ll include his contact info also – he’s someone else you definitely should be comparing notes with.

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        4. I only know a handful of individuals.. Andy Firk, Steven Cucura, the Striblings from Pine Island Nursery, Louise from the Fruit and Spice Park, and some select FGCU folk. I donated several Dipteryx seedlings to Fairchild a few years ago, but nobody wants to get back to me on if they’re alive. :/ FaSP had some from me as well but all perished — we think it needs a certain bacteria. Seeds from Trinidad won’t happen this year because of early rains. Boooo.

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  3. That is an amazing amount of work!! I have some black and green cardamom plants that I would really like to try to get them to flower. I am going to remember your ideas!

    It’s harder to leave comments because you don’t have the option to leave a comment with name/email address/website alone. It;s a comment setting you have to turn on in WordPress.

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    1. Thanks so much for commenting, Andi! I’m not super familiar with cardomom, other than knowing it’s in the ginger family. Do you think getting them through winter undamaged would allow them to flower?
      And thanks so much for the info about the WordPress commenting. I kind of have a love-hate relationship with WordPress. I love the idea of it, but so much of it seems so needlessly complex and non-intuitive, with settings hidden away somewhere in the dashboard. I thought I had set it to make it easy for people to comment, using just a name/email address/website, but I guess that’s not what settings I have in place. I’ll check my comment settings, thanks! And your medieval cooking blog looks fantastic, I had no idea such neat stuff was going on, I just followed you.

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  4. Hey Craig- sweet blog post. I really enjoyed seeing all the different methods you employ to keep things from getting frost bitten. I have a black sapote against the south facing wall of my house that’s surrounded by some shrubby ornamentals. I did some pruning and weeding a few weeks ago- trying to be proactive- but I think I overexposed it and some of the leaves got frost bitten! Oh well, the jackfruit about 8ft away was still surrounded by other vegetation and suffered no damage. Lesson learned.

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    1. Hi Patrick, thanks for commenting. Wow, super exciting that you’re experimenting with growing black sapote and jackfruit trees growing in the ground in the Gainesville area! Very exciting to hear that the canopy-protected jackfruit was untouched. For black sapote, canopy cover seems particularly critical. I didn’t mention it in the post, but I actually have two black sapote seedlings in the ground, the one I showed a pic of which is canopy-protected, and another about thirty feet away in a more exposed area. Both planted summer 2016. Last winter, canopy-protected one was untouched, and the exposed one froze to the ground, I thought it was dead till it resprouted around May or June. This year, I threw a sheet over the exposed one, did nothing to the canopy protected tree. Again, the one under the canopy had zero damage, the one just thirty feet away had substantial foliage burn (though didn’t freeze back), despite being covered by a sheet.

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      1. I have a sixty or seventy foot Jackfruit that lost about 3/4 of its leaves in the last cold snap..but still has life and new sprouting on most of the tree. The large trunk has new bumps that have developed ..I suspect those will develop into fruiting sprouts. I’m in Clearwater and usually end up many fruit, but the squirrels are horrible. Maybe the cold will have a positive effect, as many of the fruit were way too high for me to harvest, and the tree needs a pruning. My full grown Mango was fine, though the top leaves and bloom up top got burned, and some leaf drop… but small ones in the neighborhood got hit hard. Papaya lost leaves but coming back… Sapodilla and Lychee untouched.

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        1. Thanks so much for commenting, Mark. Wow, sixty to seventy feet tall is pretty big for a Central Florida jackfruit tree! I’m impressed it was able to get that big at all. Good to hear it’s sprouting out and that so many other of your fruit trees came through so well. Hopefully it’ll be another five years or so till we get another freeze this cold.

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  5. Enjoying your blog! You gave me some great ideas for the next freeze, which is — uhhh– this weekend. I only have citrus capable of handling temperatures in this 20’s (I’m in Tallahassee, only 4 miles south of the GA state line). Only young citrus trees that have been in ground less than 2 years have to be protected until they are well acclimated to this area.

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    1. Thanks for commenting, Clarke! I’m hoping the cold weather this coming week stays just above the freezing point. That’ll help keep the citrus trees dormant, so they’ll be in good shape for any subsequent freezes we get this winter. I’ve been impressed at how well citrus trees can produce in a fair bit of shade – some of my best producing tangerine trees are under a big grandma live oak, which gives them a lot of protection from cold.

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  6. Hey Craig, excellent blog sir! Thanks for making it! I thought I would just chime in some cold-weather notes for this year. We got down to 28 F so far this year. Plants under the oak: 1. The jackfruit (dang rasimi) looks ROUGH, all leaves cooked, probably a good deal of stem die-back, but I can’t tell the extent of the damage yet. 2. The little black sapote is defoliated pretty well. 3. The seedling canistel right next to the black sapote is a little burnt, but doesn’t really look all that bad, though time will tell. 4. The “ross sapote” looks fine, but it does have a closer umbrella of a low oak branch that comes down over it. South side of house: 1. muntingia, spondias purpurea, tamarind all burnt pretty harshly. BUT: 2. Sapodilla (ox) looks untouched, and 3. A little tiny green sapote (about 2 ft tall) looks untouched. North side of house: 1. White sapotes. Fruit that was peanut sized turned black and fell off, fruit that was grape sized hung on. These are just random observations, and some of these results could just be quirks of the individual plants particular locations. Anyway, keep up the great work sir!

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    1. Hi Marabou, thanks for stopping by and commenting. Excellent report – it will be interesting to see how those plants do this coming year. I’m realizing how important it is to document effects of weather events like this. I just added a few more notes to this article about effects of the second freeze – seedling mangoes are still undamaged after 24F, with no protection other than oak trees overhead.

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