An inverted mason jar gives six or seven degrees Fahrenheit of frost protection. I never would have guessed that.
I had to do this experiment twice, because I didn’t believe the results the first time. For two nights running, I left a pair of temperature loggers (digital recording thermometers) on a raised garden bed, one beneath an inverted wide-mouth quart Ball (mason) jar, one in the open.
In both cases, the goofy little mason jar provided 6 to 7 degrees of warmth. That wasn’t quite enough to prevent frost inside the jar this morning (the temperature dipped below 20F around dawn). But that is, nevertheless, an impressive amount of frost protection from a device that has, for all intents and purposes, almost zero value as either insulation or thermal mass. Continue reading G22-006: Mason jar as frost protection — a winner!
Bottom line: To protect a raised garden bed from frost, use a space blanket. Or, better yet, use a piece of construction radiant barrier. Same idea, but much tougher material. Alternatively, use glass jars to cover individual plants.
I tested these methods, using temperature data loggers, and you can get anything from 5 to 10F of frost protection from them. And all of them work the same way, by trapping the heat energy from the (relatively) warm underlying soil, that would otherwise be radiated away into the air.
By contrast, a lot of advice you’ll get on the internet — and a lot of frost-protection products offered for sale — don’t do much. In this post, I get around to testing (and flunking) the use of a sheet of polyethylene plastic as frost protection.
Free advice is worth what you pay for it. If you’re lucky.
The internet offers plenty of advice on protecting your vegetable plants from frost.
Some of that is useful, but much of it is wrong. Or, if you wish to be more charitable, much of it is almost, but not quite, completely ineffective. It’s folklore that somebody read somewhere, and passed it along without testing it to see how well it works.
Is anyone surprised?
That includes the commonly-cited advice to cover your tender plants with floating row cover, or to cover them with a frame draped with plastic sheeting (e.g., polyethylene sheet) when there is threat of frost.
Neither of which works worth a damn, by the way. Better than nothing, but not by much. Which I will show, below, using temperature data loggers to test that empirically.
In this post, I’m going to finish what I started last year, regarding the use of radiant barrier material for frost protection. Unlike a house (say), on a cold, clear, still night, a garden bed loses far more energy from radiation that from conduction. Once you’ve established a pocket of still air over your bed (and so, stopped losses via convection), you get far more bang-for-the-buck by preventing heat losses via radiation than you would by focusing solely on preventing losses to the atmosphere via conduction. Hence the use of radiant barrier material.
For those of us whose understanding of heat losses comes from insulating our homes, this may seem counterintuitive. Just keep re-reading the “Unlike a house” line above, until it sinks in. For a garden bed, the relative importance of energy loss via radiation and conduction is flip-flopped, compared to a house.
The practical upshot of that is that if all that stands between your plants and a frosty death is a sheet of plastic, consider tossing a space blanket over that. That thin layer of radiant barrier material will substantially add to the minimal frost protection offered by a plastic sheet alone.
To be clear, I didn’t think up that advice. I got the idea from a document that ultimately comes from the Colorado State University extension service (.pdf). That’s seriously useful advice from people in a seriously cold climate.
Edit: Separately, a mason jar (or any glass jar) also provides excellent frost protection for individual plants. For the same reason — it blocks long-wave infrared radiation. I tested this in Post #G22-006.
This weekend’s problem
Given how quickly the weather can turn hot in this area, I decided to get the earliest start possible on some cool-weather crops. Soil temperatures in my raised beds were at or near 50F a few weeks ago, plenty warm enough for some cold-weather crops. So I planted some peas, beets, turnips, and potatoes, even though we were more than a month away from our “last frost date”.
These have now produced nice green shoots. And, of course, now we’re going to get a frost. And yet, I’m not worried.
It’s not like I didn’t have plenty of warning. Two weeks back, the long-term weather forecast for my area gave a warning of likely frost this weekend. True to the forecast, the National Weather Service is now calling for successive nighttime lows of 27F and 26F in Northern Virginia, before returning to above-freezing temperatures.
I’m not worried, because I have my frost protection already worked out. Tested as to performance (Post G21-018). I should get adequate protection for this freeze event just by covering my raised beds with cheap, sturdy radiant barrier material. (It’s the same concept as a space blanket, but a lot tougher.) But if I’m feeling particularly paranoid, I might throw a few tens of watts worth of electric night lights under that cover, just for insurance, left over from a prior experiment (Post #1412, heated faucet cover). An idea which I also stole from the U. Colorado extension service document cited above.
In this the rest of this post, I’m going to recap the radiant barrier method of frost protection, and then push a bit beyond that. At some point, I’ll come up with a raised bed cover that provides both insulation (against loss of heat energy via conduction) and radiant barrier (against loss of heat energy by radiation). For now, though, I’m mostly going to walk through why radiant barrier is far better than either plastic sheeting or floating row cover, for providing frost protection to your sensitive plants.
Part 1: The tin-foil-hat gardener.
Above, you see one of my raised garden beds with pieces of woven polyethylene radiant barrier clipped to the top.
I went through the some of the science and math behind the use of a radiant barrier for garden beds in Post G21-015. Briefly:
While a traditional tin-foil hat serves to block alien mind control rays and other forms of incoming radiation, garden radiant barrier seeks to block outgoing radiation. In particular, it serves to prevent heat energy in the garden bed from radiating away into space. On a cold, clear night, those radiant heat losses would be large, and preventing them from occurring keeps the bed warmer than it would be, without the tin-foil-hat. So let me start this off by telling you all that you really need to know about radiant barrier.
Radiant barrier greatly reduces heat losses through radiation IF AND ONLY IF at least one clean side of the barrier faces an air gap of at least an inch.
(Or if it faces a vacuum, if you happen to be NASA. Hence the origin of the term “space blanket” for one commonly-available radiant barrier material.)
In particular, it works just as well if either side faces an air gap. Either the one facing the warm object, or the one facing the cold exterior. Which means that your intuition that this works “like a mirror for heat” is only partly right. That’s OK. Just follow the rule and it doesn’t matter if your intuition fails you. This is physics, and nothing changes just because you can’t quite get your mind around it. That’s just the way it is.
For you who need a more practical example, consider Reflectix water heater wrap, sold as “radiant barrier insulation”. The shiny outside serves as a barrier to the emission of infrared energy. Touch it and you’ll feel that it’s warm. And yet, it’s doing its job. It’s warm precisely because it’s difficult for heat energy to radiate away from that shiny, “low-emissivity” surface.
For those of you whose bent is more historical than scientific, look up pre-technology ice making in India and Iran. Under the right circumstances, upward radiative losses from a pan of water can result in the production of (some) ice even when the ambient air temperature is above freezing.
Note that the rule is very specific: This shiny material must face an air gap on at least one side.
Get it dirty, and performance degrades. Why? Because dirt is perfectly capable of radiating heat away. Transfer the heat from the aluminum to the dirt via conduction, and off it goes.
Sandwich it between two other layers and it does nothing. Why? The other materials don’t prevent radiation. They are perfectly capable of radiating heat. Conduct heat through this material, radiate it away using some other material, and the heat is gone.
Use it as a ground sheet for your sleeping bag, ditto. No air gap. Lay it on the ground and cover it with snow, likewise (I think it would be no better than having a simple plastic sheet under the snow.)
You get the drift. One clean side must be open to at least an inch of air, NASA excepted.
Choice of material
Now that I have that out of the way — one clean side must face some sort of air gap — let’s proceed.
What you see in use above is a tough woven polyethelene material, with an aluminized coating on both sides. It’s used in building construction. Here’s an example from Amazon, 62 feet of 4′ wide material, for $40 (reference). At 20 linear feet to cover a 4’x16′ bed, that works out to be about $13 to cover one 4’x16′ bed.
This stuff is very tough and reasonably cheap. Given that I use it just a few days a year, I am sure it will last decades.
There are plenty of easily-obtained alternatives for covering your beds with radiant barrier material. Really, all you need is a thin sheet of something that’s extremely shiny. Think “space blanket”.
But I think they all have significant cost or performance drawbacks relative to woven-polyethelene radiant barrier sold for building construction.
Space blankets work fine (I tested that), but they tear incredibly easily, particularly when clamped in place on a windy day. In the long run, they’ll cost more than woven poly radiant barrier. A typical thickness for space blankets is 12 microns, or about 0.5 mils (thousandths of an inch) thick.
You can buy large sheets of aluminized mylar, anything from “space blankets in bulk” to sturdier, thicker material. Here’s some that’s 2 mils thick, and costs somewhat more than half what the woven radiant barrier costs (reference). The thicker material is tough, but my experience is that it doesn’t like to make the sharp-radius curves required to clamp it to a flat surface. I suspect (but don’t know) that this wouldn’t last as woven radiant barrier.
Reflectix or equivalent should work well, but looks like it’s almost 10 times as expensive as woven poly radiant barrier. Reflectix is a tough bubble-wrap type material, shiny on both sides. Presumably that would give both radiant barrier and some modest insulation against conductive losses through the top of the bed.
Performance
Last year I did a series of experiments to show that this works. I had two cheap temperature loggers — digital recording thermometers. I left half the raised bed uncovered, and logged the overnight temperature of the uncovered and covered portions of the bed.
Here are the results:
A layer of floating row cover does nothing whatsoever. This was thin row cover, but this is also just about exactly what I expected.
A covering of literal space blanket (alone) raised the overnight temperature by about 5 degrees F:
Putting some gallon jugs to warm up during the day, and then covering with space blankets at night, raised the overnight temperatures by 10 degrees F. This had about one gallon per 8 square feet, and the gallons were warmed to about 70F by the end of the day. The results below were completely consistent with the thermal energy stored in the water, relative to the energy storage (and poor conductivity) of the underlying soil bed alone.
Doing the same, but using that heavy-duty woven polyethylene radiant barrier instead of flimsy space blankets raised the beds an estimated 12 degrees F overnight. (Estimated because the battery on the control temperature logger died overnight.)
And now, a new test. You’ll often get advice to protect your plants from freezing with some sort of frame (e.g., “hoop house”) covered by a piece of plastic sheeting. So let’s now test that.
(And, to be honest, maybe the good results above were purely from covering the bed with some type of plastic sheet. Maybe the radiant barrier property of that sheet is just a red herring. My earlier calculations say that can’t plausibly be true, but that still ought to be tested empirically.)
It’s not entirely implausible that a plastic sheet would provide some protection. A single layer of polyethylene sheet should add a roughly R 0.85 (U.S. units, not comparable to S.I. R-values). But that plastic sheet is essentially transparent to infrared, and so provides no radiant barrier whatsoever.
I addressed this question, in theory, in Post #G21-015. At that time, all things considered, I figured I would need something like 60 gallon jugs of 70 F water, to keep the garden bed 10 degrees F warmer than ambient, on a cool night, with plastic sheet alone.. Roughly speaking, a gallon jug every square foot.
Here’s a picture of the setup. I have one data logger under that tightly-tucked plastic sheet. Most of the sheet sits well away from the bed. And a second data logger in the uncovered portion of the bed.
And below you see the results. The side of the bed tightly covered in plastic sheet was less than 1 degree F warmer than the un-covered side.
Summary and further reflection in the performance of unheated plastic greenhouses.
The upshot of this is that at least two common bits of internet advice for cheap frost protection seem to be more-or-less worthless when actually put to controlled trial. Neither floating row cover nor a sealed air space covered with polyethylene plastic was able to achieve even 1 degree F of warming, on average, of the course of a night.
So, despite all the customer testimonials, I remain skeptical of the idea that you’ll be able to save your plants from a hard frost something like this:
Source: Amazon.
Or something like this:
Source: Amazon.
On the latter, real growers understand that. Go on YouTube, and you can find plenty of seemingly reputable gardeners who have measured the impact of their unheated greenhouses and will tell you that the nighttime air temperature in the greenhouse is essentially no different from that of the outside air. (e.g., just over four minutes into this episode of Gardener Scott):
If you have enough thermal mass inside the greenhouse, and the area of the walls is small enough relative to the enclosed volume (i.e., the greenhouse is large), and you have (say) a double-walled greenhouse with two layers of plastic and so much higher insulating value for the walls, then you might get several degrees of nighttime warming.
But a two-foot-tall hoop house covered by a single layer of plastic isn’t going to do much. At least, that’s what my experiment suggests.
There may be some anti-frost advantage to the hoop house, in that the higher daytime temperatures — when the solar energy does drive the interior temperature well above ambient — might heat the soil enough to provide additional energy release from that warmer soil at night. So maybe a tiny hoop house, in place day and night, might serve as enough of a solar energy storehouse that there is some material frost protection.
That said, I doubt it. My soil temperatures right now in that bed are around 50 F, but the air above the bed was essentially no different from the ambient air temperature. I can’t believe that another 10F or so in soil temperature would turn that situation around.
That said, I haven’t tested that, and probably never will. I don’t use cold frames or hoop houses because, in my experience, as an inattentive gardener, I always end up cooking my plants, one way or the other. All it takes is one unseasonably sunny and warm day, and a lack of attention, and the season’s growth can be baked to death in an afternoon.
Finally, one way in which a small single-wall hoop house can provide significant protection is in snow. If it gets covered in snow, the snow layer acts as insulation. This is no different from unprotected plants, who are more likely to survive cold temperatures if buried in snow than if exposed to the air above the snow.
I don’t deny that plastic-covered hoop houses have value. They speed growth by raising daytime temperatures well above those of the ambient air. Within reason, higher temperatures mean faster growth, all other things equal.
But if you’re going to spend $40 on a small plastic hoop house, spend an extra $2 for a space blanket to cover it in case of unexpected frost. The single wall of plastic, by itself, seems to be good for maybe 1 degree F of frost protection. Add a space blanket radiant barrier should boost that to at least 5 degrees F of protection.
Extras for experts: Wall of water and glass cloche
There are at least two other commonly-suggested ways to protect plants from freezing (other than literally heating the space the plants are in).
One of those — the Wall O’ Water (r), has physics that are completely obvious.
But the most time-honored of all – the glass cloche — is a little harder to figure out.
First, it’s no secret how a “wall of water” device can protect plants from freezing. These provide a large thermal mass in the form of 2″ wide plastic tubes filled with water, forming a deep, narrow chamber that protects the plant from excessive heat losses from convection. That mass heats during the day, radiates at night, and keeps the interior of the structure above freezing even in the face of a hard freeze.
Source: Wall-o-water.com. Accept no substitutes
Figuring out why a cloche works is a little harder. Glass choches have been in use for so long — and would have been so incredibly expensive in the past — that I have no doubt that they work to some degree. It’s just not clear why they work.
A traditional cloche is a heavy piece of glass, roughly in the shape of a bell. And yet, I’m pretty sure that unlike the Wall O’ Water (r), these don’t work by thermal mass. Near as I can tell, a mid-sized garden cloche only weighs about 6 pounds. Moreover, the specific heat of common window class is only about 0.2 (reference). As a result, a typical garden cloche would only retain as much heat as roughly 1.2 lbs (or a little over one pint) of water.
N.B. specific heat is the amount of heat energy required to raise a given weight of a substance by a given temperature. In the U.S., God help is, that’s expressed as British Thermal Units required to raise one pound of a substance by one degree F (whilst proceeding at a speed no greater than 10 knots per fortnight). Under that system, water always has specific heat of 1.0, as that is precisely how the BTU is defined.
By contrast, the specification for the genuine Wall O’ Water (r) say that it takes more than 20 pounds of water to fill it (reference).
So, what appears me to be a typical glass cloche has only about 5 percent of the thermal mass of a Wall O’ Water. Moreover, people claim that you can use a mason jar as a cloche — just place it atop your plants if a nighttime frost is predicted. Surely a thin-walled mason jar has next-to-no thermal mass. A thin-walled mason jar surely has too little thermal mass to matter.
Instead, I wonder if the effectiveness of the glass choche is due to the spectral properties of ordinary glass. Glass is transparent to near-infrared — what you’d perceive as the warmth from a glowing filament, say. But glass is opaque to medium and far infrared — the type of heat radiation that would dominate the spectrum of infrared given off by soil.
Among other things, this is why infrared cameras (e.g., a FLIR camera) do not have glass lenses (reference). In the temperature ranges where a FLIR camera might be used — such as thermal imaging of a house to look for heat losses — glass is more-or-less completely opaque. In fact, FLIR cameras cannot see through ordinary window glass for the same reason, and by report, window glass appears both opaque and reflective when viewed by a FLIR camera (reference).
And so, in the end, I suspect that my sheets of radiant barrier and a glass cloche work by the same principal — they both reflect the long-wave IR radiation that is given off by warm ground. By keeping this energy from escaping, and maintaining a still air pocket, they keep everything inside that air pocket materially warmer than the outside air.
I guess, as I put the tin-foil hat on my beds for tonight’s freeze, that’ll be another thing to test. Two temperature data loggers side-by-side, one under a mason jar, one not. I’ll report that out tomorrow.
The U.S. is now at 9.3 new cases per 100K population per day. That’s just about where we were seven days ago, and it’s a little bit of an uptick from the very lowest rate seen in the past seven days. I don’t want to read too much into that, but cases are now flat-to-up in four of the six regions on the graph below. Continue reading Post #1468: COVID-19 trend to 3/23/2022, now flat-to-up.
Can you grow potatoes in your garden by planting grocery-store potatoes? If you search the internet, you’ll find every possible answer to this simple question.
The correct answer is: It depends. But not in some wish-washy, random, some-do, some-don’t, luck-of-the-draw kind of way.
It depends on whether or not those grocery-store potatoes were treated with the sprout inhibitor chlorpropham. That substance keeps potatoes from sprouting by permanently damaging their ability to grow. And it is commonly used in the U.S., for potatoes sold at the grocery store.
Key fact: Potatoes labeled as “organic” cannot legally be treated with chlorpropham.
So, if you want to buy potatoes from the grocery store and plant them, buy potatoes labeled as organic. In five years of doing that, I’ve never had that fail.
By contrast, planting non-organic potatoes from the grocery store may or may not work. It depends on whether or not they were sprayed with chlorpropham before being shipped off to the grocery store. And there’s no way to tell, just by looking at them.
Separately, there’s more to this issue, because, unlike “seed potatoes”, grocery-store potatoes are not certified as “virus free”. But I think that’s more of an issue for commercial growers than it is for the casual home gardener.
Details follow.
The damnable thing about reality is that it keeps changing. Just when you think you have some tiny part of it figured out, somebody upsets the apple cart potato bin.
I’m not talking about the pseudo-culture-wars around the rebranding of the Potatoheads.
And I’m not referring to the consequences of the Federal Web Designer Full Employment Act. This is the 1997 Federal statute requiring that every commercial and governmental website must make significant changes in layout and functionality, any time more than half of its users have figured out how to use it.
Nope, today’s rant is about spuds at Home Depot.Bags of certified seed potatoes, for spring planting, prominently displayed for sale. These were offered with several other items I’d never seen there before, including onion sets and, of all things, pomegranate seedlings. (Apparently, hardy to USDA Zone 7 as figs are — with the occasional die-back in a hard winter.)
I don’t recall ever having seen seed potatoes at my local Home Depot, and I’m not quite sure what that implies.
Why are those potatoes there, now?
I know why I grow potatoes. I tried it in 2020, and I liked the results. I grow a modest amount of potatoes because:
They’re easy to grow.
Deer won’t eat them (so far).
They taste better than store-bought.
You get a lot of edible calories per square foot of garden.
They store well.
I figured that almost nobody in my area (northern Virginia) grew potatoes in their back yard. For one thing, our heavy clay soil is far from ideal. If you decide to get around that issue by going the “no-dig” route, your home-grown potatoes will end up costing more than store-bought (see Post #1073).
And it’s not as if the potato is some beautiful addition to the garden landscape. It’s a scruffy green plant with nondescript flowers. Not only are you supposed to clip the flowers off, you have to spend weeks looking at the dying foliage before you can dig up the crop.
And so, as of last year, this tiny part of my world made sense. Potatoes are cheap to purchase, expensive to grow in our ill-suited soil, and not much to look at in any case. And I couldn’t find seed potatoes locally. It was all completely reasonable.
You don’t see snowmobile dealerships in Florida. You don’t see masses of seed potatoes for sale in a Home Depot in the Virginia suburbs of Washington DC.
But now, my local Home Depot is offering several different varieties of pre-chitted seed potatoes.
Those don’t appear anywhere on their website. The only way to know that my local store has them it is to walk into the store and — surprise — they have enough bags of seed potatoes for hundreds of local gardeners to be growing potatoes this year. What I’m saying is, it’s not like they decided to test the waters with a few packages tucked away on a shelf somewhere. They have cardboard bins full of 1-pound bags of seed potatoes.
And they aren’t even cutesy, exotic spuds, the kind you’d market to the upscale gardeners in this area. Home Depot is offering your basic red, white, and gold potatoes, just as you’d buy in the grocery store.
And so my world view is turned upside down. Is this some new fad that has somehow passed me by? Has there been some viral potato-based meme? Is Yukon Gold the new black? Has some post-pandemic survivalist instinct kicked in? Or has there always been some quiet, underground population of potato fans in this area, and has Home Depot has finally decided to crack the lucrative home-potato market?
Change is bad. Inexplicable change is worse. What’s the take-home message when Home Depot is offering the seed stock for what amounts to cheap survival food, front-and-center in a mid-aisle display?
Can you grow potatoes bought at the grocery store? Answer: Buy organic potatoes.
Please note, I’m not saying “should you”. I’m answering the more basic question “can you”. Internet advice is all over the map. Some people swear it doesn’t work at all. Some people swear it works fine.
The real answer is, it boils down to the type of sprout-inhibiting treatment that was applied to those potatoes. And, as far as I can tell, the treatment that permanently prevents the potato from growing is not legal for use in potatoes labeled as “organic”.
So, yeah, in theory, you can use organic grocery store potatoes, with a pretty good chance they’ll grow just fine. You still risk importing potato viruses into your garden if you grow grocery-store potatoes. But advice that you literally can’t grow potatoes from grocery-store potatoes does not apply to to the sprout-inhibiting treatments legal for use on organic potatoes.
Detail follows.
If you grow potatoes, in theory, you’re supposed to use “seed potatoes”. The first time I tried potatoes, that’s what I did. I bought some on-line from a seemingly reputable dealer. It was an expensive failure. None of my super-duper seed potatoes sprouted. Given the cost (and the cost of shipping), I’m sure I’d have bought them locally if I could have found them.
Ever since that first flop, I’ve gone against standard advice, and simply bought eating potatoes locally and planted them.
That’s risky because you might introduce some long-lived potato diseases into your garden soil that way. For this reason, potatoes sold as seed potatoes must be certified as being more-or-less virus free, and commercial potato producers in most (possibly all) areas are required to plant nothing but certified seed potatoes (or something close to that, or deemed equivalent to that).
There is some internet chatter suggesting that it’s illegal for a home gardener to plant store-bought potatoes in (e.g.) Idaho. But if you actually read the statute, that doesn’t appear to be the case. In Idaho, it’s illegal to sell potatoes for planting that are not certified as disease-free seed potatoes. (For what it’s worth, that’s also what the law of the Commonwealth of Virginia says. And, I’d wager, that’s what the laws in every state say (e.g., Florida).) But in addition, in it’s illegal for commercial growers in Idaho to plant anything that is more than one generation removed from certified seed potatoes. But nothing in Idaho statute (or at least, that part of the statute) addresses home gardens.
But if you’re just a casual potato grower, probably the bigger risk is that your grocery-store potatoes may not grow. By the time you get to late winter/early spring, it’s a good bet that almost all eating potatoes you can buy from almost any source have been treated with some type of sprout inhibitor or “anti-spudding agent”. (Because, if not, given how they have to be stored so that they remain pleasingly edible, they’ll have started to sprout by that time, if not treated.)
In the U.S., commercial, non-organic food potatoes are most commonly treated with chlorpropham (reference). This is basically a powerful herbicide, and there’s enough concern over toxicity that the EU and Great Britain banned its use starting in 2019 (reference). It works by permanently damaging the ability of potato cells to reproduce. Even contamination with low levels of it greatly impacts subsequent growth of the potato plant (reference). And I noted that the concentration of Chlorpropham used in that last study was well below the 30 PPM limit on residues on food potatoes for sale in the U.S (reference, U. Idaho extension service.)
If you read about someone trying and failing to grow potatoes or getting a terrible yield, using food potatoes, or you’ve seen advice not to use store-bought potatoes, you’re probably reading about the effects of chlorpropham. If that’s been applied, there’s no way to reverse the effects. It fundamentally and permanently alters the ability of that potato to grow. (And, see above, it even stunts any successive generations of crops grown from those potatoes, if you can get them to grow in the first place).
Now we come to the $100 question: Can chlorpropham (CIPC) legally be used on U.S. potatoes marketed as organic potatoes? This University of Idaho publication pretty clearly says no, it cannot:
Alternatives to CIPC are needed for both organic and export markets—where CIPC is not permitted.
(But if you really want to be sure, you have to consult the USDA National List. If it’s a synthetic compound, and it’s not on the list, it’s not allowable for use in produce labeled organic. And, to be clear, it’s not on the list. So, not allowable for use in production of potatoes labeled as organic.)
Organic methods of potato sprout inhibition have turned to using substances that are Generally Recognized as Safe (GRAS), or that are themselves natural compounds, or that are on the USDA National List. The sprouting of potatoes stored under normal conditions can be inhibited with ethylene gas, or by application of concentrate essential oils such as clove or mint oil, or by use of hydrogen peroxide (reference, reference). You can also keep sprouting down by judicious choice of potato variety, or choice of varieties that can be stored at colder temperatures without loss of flavor/conversion of starches to sugars.
Here’s the key point: Most organic methods of sprout suppression do not permanently damage the potato. They will kill off the sprouts that are active. Some temporarily inhibit new sprouting. But they don’t prevent further sprouting, once they are stopped. In fact, one of the main drawbacks of these organic methods is that they have to be re-applied if the potatoes remain in storage. Here’s the key paragraph, from the University of Idaho publication cited above, emphasis mine:
These alternative compounds are not true “sprout inhibitors” that inhibit sprouting by interfering with cell division or some other biological process. Volatile oils and hydrogen peroxide are more correctly called sprout suppressants, as they physically damage developing sprouts with a
high concentration of the product in the surrounding headspace in the potato storage. Because of high volatility, these compounds leave behind little or no residue. Since new sprouts continue to develop, repeat applications are required at two to three week intervals or on a continuous basis.
Source: Organic and Alternative Methods for Potato Sprout Control in Storage, by Mary Jo Frazier, Nora Olsen, and Gale Kleinkopf, University of Idaho, September 2004.
Courtesy of the same University of Idaho group, you can see what a potato treated with clove oil looks like. The clove oil kills off the existing baby sprouts, leaving little black dead sprouts all over the potato. But this will not prevent the potato from re-sprouting.
Source: Potato Sprout Suppression from Clove Oil, By Nora Olsen, Mary Jo Frazier and Gale Kleinkopf
Based on the many, many bags of grocery store potatoes I looked at this spring, that picture looks awfully familiar. I’m not sure whether you truly can tell whether a potato has or has not been treated with a commercial essential-oil sprout suppressant. But I’ve noticed a lot of these little black dead sprouts on the organic potatoes at the supermarket. And I’m guessing that what I’m seeing is potatoes that have been treated with these sprout suppressants, and not chlorpropham.
For my first-ever crop of potatoes, I got mine at my nearest farmers’ market, after my boxes of seed potatoes failed to grow. That worked great. Since then, I tend to cruise the bags of organic potatoes at by local grocery stores, looking for ones that are showing the very first signs of sprouting. My experience is that if you can see those tiny little white (not black) sprouts forming, they’ll grow OK. They are already in the process of recovering from whatever organic sprout suppression treatment was applied. And getting them at the grocery store is both cheap and convenient.
In any case, potatoes are a crop where you have to get started early. By the time I saw I could buy seed potatoes at Home Depot, it was too late for this year. You’re supposed to “chit” the potatoes before you plant them, that is, get them to break dormancy and start sprouting. That chitting process takes a month or two. If you want to plant your spuds on the traditional date of Saint Patrick’s day, you have to buy them and set them to chit sometime around the end of January. So I already had a couple of trays of sprouting potatoes in my kitchen by the time I saw the commercially-available product at the Home Depot.
Finally, I repeat, you can grow them this way. Whether the casual gardener should do that is an open question. This does not address the issue of potential spread of viruses harmful to the potato. I’m not sure how common those are in food potatoes, but for sure, they are common enough that every state that I’ve looked at has standards that seed potatoes must meet. Further, if you introduce a particularly harmful virus into your garden soil, my understanding is that it effectively ruins the soil for potato production for years.
And, when you get right down to it, it’s not like there’s a huge cost savings, once you get your local big-box stores selling seed potatoes. Home Depot has certified seed potatoes $4 a pound. If the only trusted alternative is organic potatoes at the supermarket, you’re probably going to pay $2 a pound anyway. Had I known that Home Depot was going to be marketing these this year, I’m not so sure I’d have been buying and chitting organic grocery store spuds.
But, for now, it is what it is. I had one complete flop using certified seed potatoes, and excellent success (so far) using farmers’ market and organic grocery store potatoes. For now, I continue to grow mine from food potatoes. I’m not sure that it’s smart, but so far, it works. And that may change, now that my local big box has them ready-to-plant, right off the shelf.
Anyway, if you go the grocery store route, pick up a few bags, to spread your risks. Leave them out to chit. I figure, if they start putting out sprouts sitting in my kitchen, they’ll probably do just fine when I plant them in the garden. If they don’t, eat them.
William and Mary didn’t post new numbers over spring break. You also might want to take the most recent numbers with a grain of salt, again due to the impact of spring break (and the potential for cases to have occurred over spring break, but not be reported to W*M).
Those caveats aside, taken at face value, the new-case rate on the William and Mary campus now appears to be on a par with the rate for 18-24 year olds, generally, in Virginia. Really, the new case rate is so low (under one per day, as I calculate it, for this last reporting period) that, effectively, you’re looking at two numbers that are effectively zero, plus some random statistical noise.
Source: Calculated from William and Mary COVID-19 dashboard. I gap-filled the 3/14/2022 number by taking the average of the week before and the week after. The 3/21/2022 rate assumes that if cases occurred over spring break, that would have been reported to W&M. No idea whether that’s reasonable or not.
For the fifth day running, the U.S. shows just over 9 new COVID-19 cases per 100K population per day. Over the past 7 days, the new case rate fell just 7%. My guess is, this is as good as it gets, for now.
Data source for this and other graphs of new case counts: Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 3/22/2022, from https://github.com/nytimes/covid-19-data.” The NY Times U.S. tracking page 3may be found at https://www.nytimes.com/interactive/2020/us/coronavirus-us-cases.html
Looking forward, we have a few countervailing forces at work now.
On the one hand, the continued spread of son-of-Omicron (BA.2) and continued decline in all sorts of COVID-19 hygiene suggest rates will rise from here.
On the other hand, I think the weather is in our favor. Everyone expect a strong seasonality to COVID-19 in the U.S., both because it has shown winter peaks two years running, and because most other coronaviruses also peak in the wintertime.
I’ve been showing a graph of this-year-versus-last year, starting with the start of the U.S. pandemic. Now let me shift that to calendar years, so you can see what I’m talking about.
It’s tough to see the pure seasonality of it because we have not reached a steady-state. Variants kept changing. Each successful new COVID-19 variant generated its own wave, overlaying any seasonal pattern that might exist. The level of population immunity keeps changing, both from vaccination and prior infection.
But let me try to abstract from all that by doing the lowest-of-the-low data analysis: fitting a polynomial trend. In this case, since my point is to try to boil this down to simple seasonality over the year, I’m going to fit a quadratic. That’s just enough to give me one peak and one trough, if that’s what the data suggest.
Here are 2020 and 2021, with a quadratic trend fitted, trying to boil the data down to a simple seasonal pattern. On this log-scale chart, you get a remarkbly similar trend line, despite major differences in the actual progress of case counts over the year. In 2022, for example, we had both the Alpha and Delta waves, and the start of the Omicron wave.
And now here’s 2022 actual data through the most current day, plotted against those two “seasonality” quadratic curves from the prior years:
My sole point here is that the apparent seasonality of COVID-19 in the U.S. should be working to depress new case counts now.
Or, more simply, for the past two years running, the lowest case counts occurred mid-June, the highest ones occurred mid-January. If that keeps up, then the forces of seasonality are in our favor.
The U.S. now stands at 9 new COVID-19 cases per 100K population per day. Plus or minus a little statistical noise, that’s where it’s been for the past four days. In all likelihood, I’d guess that we’ve now reached the bottom of our Omicron wave.
Data source for this and other graphs of new case counts: Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 3/22/2022, from https://github.com/nytimes/covid-19-data.” The NY Times U.S. tracking page may be found at https://www.nytimes.com/interactive/2020/us/coronavirus-us-cases.html
Obviously, one way to deal with this is to declare victory. Particularly if this is as good as it gets.
But a thoughtful person might be keeping an eye on the U.K., where they are going straight from their Omicron wave into their son-of-Omicron (BA.2) wave. At present, the incidence of new cases there is 20 times the level seen in the U.S.:
Source: Johns Hopkins data via Google search.
But the good news for the U.S. is that there’s still no sign of an upturn in new case rates, even among the states that reached their Omicron wave peaks first. The graph below divides states into five groups based on the date on which their Omicron case rate peaked. There’s about a two-week difference in peak date between the early-peak states and the late-peak states. And yet, the only difference is that the latest-peak states continue to show falling new-case rates. All the other categories merely show a stable rate for the past week or so.
The upshot is that whatever is happening in the U.K. (and Australia, below), isn’t happening in the U.S., yet.
Source: Johns Hopkins data via Google search.
One surprise from today’s data is that son-of-Omicrion (BA.2), the more-contagious variant of Omicron, is not spreading as fast as expected in the U.S. As of the most recent CDC data published today, that still only accounted for about a third of new cases. New case rates in the U.K. didn’t really start to take off until BA.2 became the dominant strain (and they cancelled all of their COVID-19 hygiene mandates).
Plausibly, that’s related to the lack of upturn in the U.S. compared to other parts of the world.
Anyway, I look at those two bits of data — the international situation, and the slower-than-expected growth of BA.2 in the U.S., and my conclusion is that it’s still a bit early to say we’re not going to follow in the same path as the U.K.
In the U.S., we can ignore COVID-19 for the time being because it now poses a much lower total risk (for hospitalization, and probably for death) than typical seasonal flu does, for those who are vaccinated and boostered. Really, in terms of your overall odds, it’s now less dangerous than flu.
