Category: Garden

Posts about gardening and related topics, such as canning and maybe other aspects of food preservation.

Post G22-015: First test of tote-based food dehydrator, version 2

 

Construction details are given in Post G22-014.

Bottom line:  Works just fine if you ventilate it with a computer fan.  Leaving this outside on two consecutive chilly, dry, sunny days was adequate to get 1/4″ potato slices dry enough to snap crisply when bent.

It was a little cold yesterday for solar food dehydration, not expected to top 60F.  But it was sunny and dry.  And that was enough to let me test and refine my revised tote-based food dehydrator (Post G22-014).   This is nothing more than an under-bed plastic tote with a bit of radiant barrier insulation outside, some cheap cooling racks inside, and a few holes in the top connected to thin plastic pipe.

Continue reading Post G22-015: First test of tote-based food dehydrator, version 2

Post G22-014: Plastic tote food dehydrator, version 2: Construction.

 

Edit:  See Post G22-015. Skip the drying racks, just place the food directly on the floor of the tote.  Replace the ventilation “chimney” with a computer fan.  With those changes, two days in the sun produced perfectly dry potato slices.

Last fall I came up with what I hoped would be a cheap and simple solar food dryer capable of drying tomatoes in the humid climate of Virginia. Continue reading Post G22-014: Plastic tote food dehydrator, version 2: Construction.

Post #G22-013: Toward a theological and horticultural theory of parthenocarpic zucchini.

Edit 7/29/2022:  Read post G22-050 first.

Theological and horticultural background

A parthenocarpic plant is one that produces fruit without fertilization, that is, without pollination.  The resulting fruits are sterile and lack fully-developed seeds.

Without getting into the deeper theological aspects, the word derives from the Greek “parthenos”, meaning virgin.   And “carp”,  meaning to complain.  Thus,  the Parthenon is a temple to Athena, who was virgin who had few complaints.

(Technically, carp means seed.  So parthenocarp means “virgin seed”.  I like my version better.)

Of course, now that you know the word, examples crop up everywhere.  The banana is almost surely the most familiar example of a parthenocarpic fruit.  If you’ve ever wondered why bananas are seedless, now you know.  It’s due to their parthenocarpic nature.

Every parthenocarpic fruit is more-or-less seedless, but not every seedless fruit is parthenocarpic.  Some still require fertilization, they just don’t (or rarely) produce fully mature seeds.  Seedless watermelons fall into that category.  Unlike true parthenocarpic plants, seedless watermelons must be pollinated to bear fruit.  The term of art there is “stenospermocarpic”, which seems to be Greek for narrow fertilized seeds.

This is also not to be confused with plants that require pollination, but not pollinators.  Those include plants that are “wind pollinated” (like most cereal grains), and plants that may be “self-pollinating” due to perfect flowers containing both male and female parts, so that simply shaking the flower may sometimes pollinate it.  (This is the source of the electric toothbrush hack for ensuring good tomato pollination.)

Parthenocarpic cucumbers and summer squash.

Greenhouse and poly-tunnel farmers provide the commercial demand for parthenocarpic varieties of common garden plants such as cucumbers and squash.  In those enclosed environments, without bees, those crops would otherwise have to be pollinated by hand.  That’s an obviously labor-intensive step, and may be a practical impossibility for crops grown under low “hoop house” type row covers.

Several different varieties of parthenocarpic cucumbers and squash are available to the U.S. home gardener. I’ve been compiling a list, but I’ve limited it to the small subset of fruits that appear more-or-less identical to their seeded, pollination-requiring cousins.  The subset of interest to me includes:

Cucumbers:  H-19 Little Leaf, Corintino, Dive, Excelsior, Piccolino, Quirk

Squash: Venus, Part(h)enon, Burpee’s Sure Thing, Defender, Duntoo, Dunja, Cavili, Golden Glory.

(Parthenon or Partenon, sure.  But Venus?  Singularly inappropriate.)

As far as I can tell, these are exclusively F1 (first-generation) hybrids.  (Because, seedless, right?)  So if you will only grown heirloom plants, or those from which seeds can be saved, this is not for you.

To determine which varieties to grow I will apply the Tomato Paralysis cure from Post G22-001.  List in hand, I’ll cruise the seed racks at my local garden center and grow whichever of those they carry locally.

As a bonus, I can have my very own guilt-free arena of death.

I ended up here because I had such a dismal time trying to grow cucumbers and summer squash for the last couple of years.

The squash vine borer is present in this area (Virginia Zone 7) for a couple of months.  That is, more-or-less for the entire squash growing season.  If you restrict yourself to relatively short-lived pesticides (I used spinosad), controlling it requires careful spraying at five-to-seven day intervals. See Post #G27, A Treatise on the Squash Vine Borer.

The cucumber beetle was essentially absent from my first year of gardening, and I had a bounteous crop of cukes.  But by my second year I had built up an unstoppable population of them, and got almost no cucumbers whatsoever.  I never found a way to control the cucumber beetle that a) worked and b) was acceptable to me, in terms of environmental impact.

The damned things are like vampires:  All it takes is one bite.  Cucumber beetles spread bacterial wilt.  So it’s not the actual leaf and blossom damage from their feeding that matters.  It’s that any feeding at all infects the plant and kills it.  As far as I can tell, a) once bacterial wilt starts, it’s just a short while until the entire cucumber plant is dead, and b) “wilt-resistant” cucumber varieties aren’t, they end up just as dead as non-resistant varieties.

But if I don’t need pollinators, I can grow summer squash and cucumbers under insect netting/row cover.  In theory, if I can sterilize the soil under the plants (with a neem oil soil drench, perhaps), and keep a bug-proof enclosure over the plants, I can physically prevent those pests from reaching the plants.  And yet have a crop, because barring the bees entry does these plants no harm.

I’ve been hesitant to try this.  Not just because it seems like a lot of work to set up, and a lot of hassle to maintain.  But because of the “vampire” nature of cucumber beetles.  It’s not their feeding that matters directly, it’s the disease they carry.  If a single beetle breaches the defensive perimeter, it’s game over for the cucumbers.  Do I really think I can (e.g.) lift the cover off to pick the ripe fruit and set it back again without letting in a single cucumber beetle?

It seemed to be a fairly non-robust setup.  I understand that insect netting can greatly reduce insect damage.  But because of the nature of the beast — bacterial wilt — I really need to eliminate it entirely.  If the endpoint is going to be a bed of deceased cucumber plants, I know ways to achieve that with a lot less effort.

But if the bees and butterflies can’t get in … then nothing bars me from making that enclosed garden bed an arena of death.  All of those highly-effective (i.e., deadly) pesticides that I normally won’t touch due to bee toxicity are now back on the table.  Subject to some constraints, nothing need stop me from hosing the bed down with (e.g.) pyrethrins on a regular basis (subject to controlling runoff).  This means I can install a secondary, chemical line of defense beneath the primary (physical) barrier.   If need be.

I’m looking for parthenocarpic, not carcinogenic.  So it’s not like any pesticide is fair game.  But cheap, short-lived and effective organics like pyrethrins would seem to be plausible.  Once I screen in the bed, I no longer have to worry about killing off my local bees and butterflies.  More-or-less any bug that gets through the outer defenses is fair game.

Conclusion

Anything worth doing is worth over-doing.  Given how much hassle it’s likely to be to do this at all, I think I’ll go for more, rather than less.

My plan is to dedicate one entire raised bed to parthenocarpic cucumbers and squash.  Roughly 4′ x 16′ or so.

Plausibly the major expense will be for the requisite statue of Athena, so that I may dedicate my parthenocarpic garden appropriately.  And some large-economy-sized Bucket-o’-Death, to ensure that any bug making it past the cover will die ASAP.

Otherwise, for me, this requires no investment in materials.  I already own a more-than-lifetime supply of thin floating row cover.  As well as a pile of loose PVC pipe and fittings, which is to adults what Tinker-Toys are to kids.

A year ago, I didn’t even know that such a thing as parthenocarpic squash existed.  This year, I’m going to grow a bed of it.   I’ll let you know how it turns out.

 

Post G22-011: Canning lids, from shortage to wide-mouth surcharge.

Above:  Used Ball lids.  The one on the left clearly shows the groove left by the canning jar.  The one on the right was boiled for 20 minutes, which flattened that groove considerably.  I picked up this tip boiling lids if you plan to re-use them from the blog A Traditional Life.

One of the many U.S. shortages that occurred during  the COVID-19 pandemic was a shortage of lids for use in home canning.  I’ve posted extensively on that here. Continue reading Post G22-011: Canning lids, from shortage to wide-mouth surcharge.

Post G22-010: Energy required for various methods of preserving tomatoes at home.

 

Source:  Wayfair

The vacuum sealer is that rare device that serves as both a kitchen appliance and a source of entertainment.  Every time I run my new Nesco VS-09, I practically want to applaud when it finishes.

I don’t normally give much thought to air.  Until it’s all gone.  Then the arithmetic of 15 pounds per square inch leads to the realization that this goofy little countertop appliance generates a literal half-ton of crushing force on a 6″ x 10″ pint-sized bag.

But I digress.  I actually bought this for the serious purpose of preserving garden produce.  The fact that I find the process and results to be so entertaining is just icing on the (perfectly flat half-inch thick piece of) cake.

In any event, there is a serious purpose to this post.  And that is to show that if you have a freezer that’s already running, then freezing your tomatoes is by far the most energy-efficient way to preserve them.  The only method that would beat that is solar drying, and I haven’t quite figured out how to do that well in my humid Virginia climate.

 

Tomatoes as freezer free-riders.

The last thing I need is another kitchen appliance.

But I bought this vacuum sealer anyway, after thinking through all the food preservation I did last year.  Of all the pickling, canning, drying, and freezing, by far, the tastiest, most garden-fresh results came from freezing.  With drying (dried tomatoes) a close second, due to the intense flavors that produces.

And so, purely from a quality standpoint, for tomatoes to be used in soups and stews,  my wife and I agree that freezing is the best option.  It preserves that fresh tomato taste. But how does it stack up in terms of energy use?

Freezing gets a bad rap, as a means of home food preservation, for its relatively high energy use.  But I think that’s not entirely correct.

If you run a freezer expressly for the purpose of preserving garden produce, then, sure, I’d bet that freezing has a fairly high energy cost.  In that case, you’d have to pro-rate the annual electricity use of that freezer over the pounds of produce preserved.  (Because, by assumption, you wouldn’t be running that freezer if you weren’t using it to preserve your garden produce.)

Just tossing out some round numbers, based on past experience, I’d bet that a typical 15-cubic-foot chest freezer has enough space to store 300 pounds of produce, and consumes about 300 kilowatt-hours (KWH) of electricity per year.

So, roughly speaking, if you run that freezer because you use it to preserve your produce, you’d consume about 1 KWH of energy for every pound of produce preserved. 

By contrast, if you are already running a freezer, and will continue to run it regardless, and you have the space, then freezing your produce only costs you the energy needed to freeze it in the first place.   The cost of running the filled freezer doesn’t count, because you’d bear that cost in any case.

My fridge comes with a big freezer.  It’s not like I’m planning to unplug that any time soon.  And so, I’m perfectly happy to let my frozen garden produce be a free rider here — taking advantage of the fact that the freezer is running, but not being asked to “pay” for it.

In that case, the only additional energy cost is the cost of getting the room-temperature produce down to the 0 F temperature of the freezer.  Given that  (e.g.) tomatoes are 94% water, that’s more or less the energy required to bring one pound of room temperature water down to 0 F.  Including the one BTU per pound required to cool the water, and the 144 BTUs per pound required to convert to ice, that works out to (70 + 144 =) 214 BTUs, or (at 3.4 BTUs per watt-hour) 63 watt-hours.  So, if you are just tossing your produce into a freezer that is going to be running in any case, freezing it takes 0.063 KWH for every pound of produce preserved.

You might think that’s a bit of a cheat, because one way or the other, you’ll want to peel those tomatoes before you use them.  The most typical methods for peeling them involve heat (either boiling water, or holding them in the flame of a gas stove).  But — surprise — it’s actually a snap to peel them after they’ve been frozen, per this YouTube video.

Take a look around 47 seconds into that video.  My jaw dropped just after the tomato did.  I know the term life-changing is overused, so let’s just say this was a tomato-life changing revelation for me.  As in, I’m never going blanch and peel a tomato ever again.  Arguably, it may actually take less energy to freeze-and-peel than to blanch-and-peel, what with the energy costs required to boil the water and cool the tomato afterwards.

Other preservation methods

I have already tracked the energy costs of preserving by canning or drying, in various earlier posts.  Let me bring all of that together in one place, below.

Drying tomatoes in my four-tray Nesco dehydrator consumed 8 KWH of electricity (per Post G21-049).  That was in the humid outdoor Virginia summer.  I am fairly sure that each tray can hold less than a pound of quarter-inch-thick tomato slices,, but a) I could stack up to 12 trays at a time for drying, and b) those were very “wet” slicing tomatoes, not the paste tomatoes that are normally used for drying.  That said, for illustration, let me just assume one pound per tray, four trays, yield 2 KWH for every pound of produce preserved.

Canning tomatoes in a water-bath canner consumes a considerable amount of energy as well.  I did the full workup on the energy cost of home canning two years ago, in Post #G22.   I had to do that because, as far as I can see, the rigorous research literature on this crucial topic looks like this:

 

In any case, the all-in energy cost for canning five quarts of pickles, on a gas stove, in an air-conditioned house, was 5528 kilocalories (kcal).

Source:  Post #G22.

Per the USDA guide to home canning, quarts of pickles require a much shorter processing (boiling) ,time (15 minutes) compared to quarts of tomatoes (45 minutes) in a water-bath canner.

Based on my prior calculation (shown above), I need to add another 800 Kcal to account for that, bringing the total up to 5300 Kcal for 5 quarts (= 10 pounds) of tomatoes.  At 1.16 watt-hours per kilocalorie, that works out to be 0.6 KWH for every pound of produce preserved.

I should note that this is a little conservative, because you have to peel the tomatoes first.  That’s going to involve a little additional boiling time.  But with all the boiling that’s taking place with the canning, I figured that was more-or-less rounding error.

Finally, I can take a rough guess at the energy cost of my crock-pot spaghetti sauce.  Crock-pot spaghetti sauce (Post #G21-048) absolutely minimizes the labor input, and is idiot-proof to boot.  But it requires processing tomatoes in both a pressure cooker (briefly) and a crock-pot (overnight).  For four quarts (eight pounds), the crock-pot portion uses about 4 KWH. But the pressure-cooker portion (20 minutes at pressure) likely used almost as much energy as canning, so for four quarts I need to add one-third of my pickle canning estimate above, which, by the time all the arithmetical dust has settled, adds another 2 KWH.  Or a total of 6 KWH for 8 pounds of tomatoes, or 0.75 KWH for every pound of produce preserved.

Edit, fall 2024:  In hindsight, that’s much more energy-intensive than a more traditional reduce-it-on-the-stove approach to making tomato sauce.  A crock pot is, in fact, a terrible (but idiot-proof) choice if you want to evaporate water out of a sauce.  I’ve gone back to making my spaghetti sauce by boiling down tomatoes on the stove, like a normal person.  I still briefly pressure-cook, dump in a strainer to remove the liquid, pass the solids though a Foley mill to remove the skins, then reduce.  This allows me to use all types of tomatoes, including salad and cherry tomatoes, without having to peel or seed them first.

There’s no additional energy cost for peeling in this method, because the entire batch of tomatoes is run through a Foley mill after pressure-cooking.  That takes out the peels and (most of) the seeds.

Let me now produce the nice neat table of energy required for food preservation, all of it expressed in terms of KWH of energy per pound of produce preserved.

All of that comes with some caveats.  The canning was done on a gas stove in an air-conditioned house.  The drying was done outside, in humid air.  I could dry up to twelve trays at once, instead of the four that I already owned.  Maybe there’s a little more energy required for the blanch-and-peel step in some methods.  And so on.

Nevertheless, the results are so clear as to be undeniable.  (So clear that I double-checked that freezer math a couple of times).  If you have space in your freezer, and you’re going to run that freezer anyway, by far the most energy-efficient way to preserve tomatoes is to toss them in the freezer.  And, per that YouTube video above, peel them as you thaw and use them.

I surely need to mention the one common method that isn’t on the list, solar (or open-air) drying.  Plausibly that has zero energy cost, but I have not (yet) figured out how to do that in my humid Virginia climate.  I’m already working on how I’m going to improve my simple $18 plastic-tote food dryer (Post #G21-049).  The solution might be as easy as “don’t overload it”.

Two minor caveats:   COP and GHG sold separately.

Two minor factors make this conclusion somewhat less that complete.  Those are coefficient of performance (COP) of a freezer, and the different rate of greenhouse gas (GHG) emissions for natural gas and electricity used in the home.  Near as I can tell, neither of these results in any material change in the relative efficiency of the various preservation methods.

First, this calculation isn’t complete because it doesn’t factor in the energy conversion efficiency or coefficient of performance (COP) of refrigerators or freezers.  The coefficient of performance for a heat pump is the amount of heat energy it can move, for a given amount of electricity supplied to it.  Almost all commercially-used heat pumps have a COP greater than 1.0.  That is, they can move more than 1 KWH of heat energy for every KWH of electricity they consume.  COPs for modern AC or heat pump units typically run around 2.5 to 3.5 (per the link above).

The estimate above — 0.063 KWH — is the amount of heat that needs to be (re)moved from the interior of the freezer.  It will actually take less than 0.063 KWH to do that, because fridges and freezers are just another form of heat pump with a COP greater than one. While Wikipedia (cited above) assures me that they have a COP greater than 1.0, I have yet to find a source that will pin that down further. The best I’ve found is a passing reference to a COP of around 1.0 for a deep freeze unit (per this reference).

The bottom line is that a typical home freezer might use somewhat less than 0.063 KWH to remove 0.063 KWH of heat energy from its interior.  But how much less, I can’t find the source that will let me pin that down.  I suspect that, given the large temperature differential between interior and exterior, the COP of most freezers isn’t much higher than 1.0 or so.

Finally, KWH is not the same as GHG (greenhouse gases).  This only measures energy consumed within the home, and does not differentiate between natural gas and electricity.  Fossil-fuel based electrical generation is far from 100% efficient, so the actual amount of fuel consumed (to generate the electricity) is a low multiple of the energy actually delivered to the house.  But in addition, electrical generation consists of a mix of generation sources, some of which create greenhouse gases, some of which do not.  If the ultimate question is one of carbon footprint, we’d have to modify this calculation, treat electricity and natural gas separately, and then redo it for some assumed electrical generation mix.

That said, when I take a rough cut at the difference between natural gas (burned in a stove) and electricity (produced with a typical U.S. generating mix), I’m not sure that adjusting for each fuel type separately would make much difference.

Natural gas releases 100% of its energy within the home.  But a typical natural gas stove is only about 40% efficient.  That’s the energy that goes into whatever you are trying to cook, with the rest simply serving to heat up the kitchen.  Basically, for every 100 units of C02 produced, you get 40 units of usable energy from your gas stove (Whatever units might mean, in this case).

For electricity, by contrast, the amount of fuel burned at the generating plant is far more than the amount that makes it into your home.  But once it gets to your home, I’ve either directly measured 100% of what was consumed, or the theoretical calculation (for freezing) should be close to that.  And so, as with natural gas, for every 100 units of C02 produced in generating electricity, you get X units of usable energy in the home.

The problem is that X depends on the generating mix that feeds your particular section of the grid.  Even so, let me do the arithmetic for Virginia’s electrical grid.

Last time I checked, Virginia’s electrical grid released 0.7 pounds of CO2 per KWH of electricity delivered.  Starting from that, I’m going to compare C02/KWH of usable energy for the Virginia grid versus a 40 percent efficient gas stove.

The EPA shows that burning a therm of natural gas releases an average of 0.0053 metric tons of C02.  At 2204 pounds per metric ton, that’s 11.7 pounds of C02 per therm.  A therm is 100,000 BTUs, and there are 3.4 BTUs per watt-hour.

Slapping that all together, burning a therm of natural gas produces 11.7 pounds of C02 and 29.4 KWH of (heat) energy, or 0.4 lbs C02 per KWH.

But a natural gas stove is only 40% efficient.  A stove has to use (1/.40 =) 2.5x as much natural gas to deliver that usable KWH of heat.  The bottom line is that a 40 percent efficient natural gas stove releases 1.0 pounds C02 for every usable KWH of heat delivered in the home.

And so, per KWH of usable energy, in terms of GHG emissions, electricity (in Virginia, at 0.7 lbs C02 per usable KWH) is slightly cleaner than natural gas burned in a (typical) 40 percent efficient stove.  But only slightly.  So the electrical options actually perform a little bit better than shown in the table above, relative to the gas-stove-intensive canning. 

There’s nothing in any of that to change the conclusion that tossing your tomatoes into a freezer that would be running in any case is by far the most energy-efficient way to preserve them.

So, what about that vacuum sealer?

All of the above brings me back to my new toy, the vacuum sealer.  If I’m going to freeze my tomatoes, the binding constraint is now the space they take up in the freezer, and secondarily, the length of time they’ll last once frozen.  Both of which will be best addressed by vacuum-sealing them.

Most sources suggest that you freeze the tomatoes before vacuum-sealing.  But at least one source shows tomato chunks that were vacuum-sealed and then frozen.  That’s what I’m now aiming to do, only using whole tomatoes, not chunks.  Given the literal tons of force that one of these sealers can generate, I’ll have to use the setting that allows the strength of the vacuum to be controlled manually.  In the end, I’m aiming for a freezer stocked with nice, flat, well-preserved packages of energy-efficient frozen tomatoes.

With any luck, we’ll see how that all plays out in a few months.

 

Post G22-009, the second-biggest waste of time in the U.S.A.

Traditional, unconditional, last-frost date

I had planted a few cold-hardy vegetables in my garden weeks prior to last weekend’s deep freeze.  I put in some snow peas, potatoes, beets, garlic, onions. 

It got down below 20F briefly on one of those nights.  I can now say that all of those appear to have survived, with just a bit of TLC.   That was in the form of capping the bed with radiant barrier, then adding a piece of plastic for air-tightness.  (See Post G21-018, or my just-prior garden posts.)

It’s no surprise that we had a freeze.  Our nominal “last frost date” is somewhere around April 22,so these plants were in the ground almost two months ahead of that.  Instead, the interesting thing is that I had two weeks’ warning that the freeze would occur.  The fourteen-day forecast accurately predicted that there would be a freeze that weekend, although the original forecasts understated the depth of that freeze.

This leads me to ponder the implications of reasonably-accurate long range weather forecasting and our “last-frost” dates.  Folklore guidelines (“plant peas on St. Patrick’s Day”) and science-based “last frost date” guidelines predate the era of supercomputers that make long-range forecasting possible.   Weather is still chaotic in the mathematical sense, and so not predictable at very long intervals, but we now have two-weeks-ahead temperature forecasts that are reasonably accurate.

I already rang the changes on this once, in post G21-005, Your 70th percentile last frost date is actually your 90th percentile last frost date.  What you typically see cited as your “last frost date” is the date on which, historically, frost only occurred after that date around 30 percent of the time.  But that’s an unconditional probability, as if you would plant on that date regardless.  If, by contrast, you check your 14-day forecast on that date, and refrain from planting if frost is in the forecast, then you’ll convert that to a 90th percentile last-frost date.  That conditional probability — chance of frost after that date, conditional on a frost-free 14-day forecast — gives you a much higher chance of avoiding a freeze after that date.

The upshot is that a reasonable prediction of the two weeks following the “last frost date” shifts the odds attached to that date considerably.  It’s actually a lot safer to plant frost-sensitive plants on that date, in the modern world, than it was in the era when no forecasts extended more than three days.  As long as you make that decision conditional on the extended forecast, and you’re smart enough not to plant if it looks like frost any time in the next two weeks.

At present, we’re creeping up on 14 days prior to our April 22 “last frost date”. And I’m pondering — just as an exercise in probability and statistics — whether that same math works 14 days in advance of the date. 

And I’m pretty sure it does.  If the 14-day forecast were completely accurate, then the conditional 70th percentile last frost date in this area would be April 9th.  No frost in the forecast through April 22 would mean that the conditional odds of frost occurring after April 9 would be the same as the unconditional odds after April 22.

That is, April 9 is our conditional 70th percentile last frost date.  If we have a decidedly frost-free 14 day forecast at that point, planting on that date bears the same risk of frost damage as planting blindly on April 22.

The only uncertainty there is in how accurate the 14-day forecast actually is, for daily low temperature.

Weather forecasts seem to be one of the few true ephemera of the digital age.  They are published, and then they are replaced with the next day’s forecast.  Nobody cares about yesterday’s forecast, other than those who have some deep professional interest in forecast accuracy.  Accordingly, where you can look up the actual weather 14 days ago, I haven’t yet located a database that lets me look up the actual weather forecast 14 days ago.

So that’s going to have to remain an unknown, for the time being, unless I want to try to compile the data, for my location, day-by-day, myself.  Or if I can find existing research that addresses this exact question of predicting a frost.  So I’ll just have to leave that as saying that if the 14-day forecast shows lows that are well above freezing, then you can probably move your traditional (unconditional) 70th percentile last-frost date up by two weeks.

But is this just the second-biggest waste of time in the U.S.?

The second-biggest waste of time in the U.S.A. is doing something really well that doesn’t need to be done at all.  (I heard that in a time-use seminar I attended decades ago.)

In the fall, frost protection has some clear advantages.   The plants are already grown, the produce is already ripening.  Protection from an unexpected early frost is a matter of saving garden produce that would otherwise be lost.

But as I hustle about protecting my plants in the spring, it invites the obvious question:  Just how much am I gaining by planting these crops early? And to that, I will add not just planting early, but the whole process of starting seeds indoors, regardless of the planting date.

In reality, is this really just an example of the second-biggest waste of time in the U.S.?

Ultimately, while some plants may grow in the cold, they tend to grow slowly.  At some level, that’s just basic chemistry.  The rate at which a typical chemical reaction proceeds roughly doubles with every 10 degrees C of temperature increase.  Sure, plants will develop enzymes to speed those processes in colder temperatures.  But it doesn’t take a genius to notice that while they will grow, they sure won’t grow very fast.

What prompts this is my peas, which are now all of about 2″ high.  And it’s getting on close to a month after they went into the ground.  Is  that head start worth it, compared to simply waiting for the nominal last-frost date and planting them then?

In short, I’m beginning to suspect that my current setup — plant early, provide frost protection, but no greenhouse — might just be the least efficient of all possible worlds.  All the hassle of early planting, and (almost) none of the benefit.

Without a greenhouse structure (or poly tunnel, or similar) to warm the daytime air and soil temperatures, it seems like most of what I’ve done is to induce my plants to try to grow under inhospitable conditions.  And they are responding accordingly.

Back when I was a low-effort gardener, I seldom mucked around with any type of early planting.  I’d start seeds a couple of weeks before I planted them, just to be able to have a tiny visible plant to stick in the ground.  (And so, have better chance of survival for (say) tomato plants.)  But my opinion then was that the gains from very early planting were minimal.  Give it a couple of weeks, and the (e.g.) peas planted later in the year will have effectively caught up with those planted earlier.

As a result, I’m now wondering whether I’ve been taking all this early-planting advice from people who do early planting and have some type of greenhouse arrangement on top of those early plantings.  From what I’m observing so far, that would make a lot more sense than just sticking plants in the ground and protecting them from freezing as needed.

When I briefly Google for this topic, all I see is people touting the benefits of early planting.  In effect, a series of statements that you’ll get more out of your garden if you do it.  I’m not seeing any quantification of just how much more you get, from early planting alone (i.e., with frost protection but not a greenhouse or poly tunnel).

So, before I get any further caught up in this effort to see just how much I can push that last-frost date, and just how well I can protect those tender plants from frost, it seems like I need to assess the cost/benefit tradeoff.

I’ve proven that I can plant well in advance of that last-frost date.  I can do that very well, thank you.  But should I do that?  I don’t think I’ve really answered that question.  And, in particular, should I do that without some sort of setup to warm the daytime air and soil temperatures?

Maybe early planting without a greenhouse really is just the gardening equivalent of the second-biggest waste of time in the U.S.A.  Clearly, that needs to be the next thing I test.  For that, I need some sort of cheap, safe, low-effort greenhouse or poly tunnel.  One that minimizes the chances that I’m going to bake my plants to death.

So that’s the next thing on the agenda.  Replant what’s in my garden, one month after the original planting date. And work up a greenhouse covering that, as a lazy gardener, I can live with.

Post G22-008: Plastic cloche surprise, not all plastics are created equal.

 

Background

In my last experiment, I showed how well a Ball (mason) jar worked as frost protection.  In the coldest part of the night, the inside of the jar stayed 10 degrees F warmer than the outside.  I thought that was exceptional performance for a lightweight uninsulated glass container.  My explanation is that the glass traps long-wave infrared.  And so, this works for the same reason that my radiant-barrier frost protection works.  It prevents the garden bed from radiating heat energy off into space.

Long-wave infrared absorption would explain why glass worked well but polyethylene sheet was a near-total failure.  A sheet of ordinary window glass will absorb about 86% of long-wave infrared, and reflect the rest.  Polyethylene, by contrast, was reported to be almost completely transparent to infrared.

Accordingly, where a glass jar works well as a garden cloche, I figured that a plastic jar would not.  And that’s what I tested last night.

Never let facts get in the way of a good argument.

There’s just one problem:  Different plastics have different infrared absorption spectra.  And it took me a while to track that down.

Using Wein’s Law, the spectrum of radiation emitted by my 50 F garden subsoil would peak somewhere around:

  • 10 microns (micrometers) wavelength
  • 10,000 nanometers wavelength
  • 1000 waves per centimeter.

Those are three ways of saying the exact same thing.

So I wanted to find out how different plastics behaved with respect to long-wave radiation somewhere in that vicinity.  That’s where most of the power from the upwelling long-wave radiation from the garden bed will be concentrated.

I never did find exactly the data that I wanted.  But I came close.  And, as it turns out, polyethylene’s absolute transparency in that region of the spectrum is the exception among plastics, not the rule.

The chart below show the absorbance spectra of various common plastics, with the long-wave infrared region highlighted.   Note that the line for polyethylene is almost completely flat in that region.  It absorbs almost no long-wave infrared.   But PETE plastic, just below that, in fact absorbs infrared strongly right at the frequency where infrared from the soil will have its peak — wave number of 1000.

Source:  Figure 9, “Identification of black microplastics using long-wavelength infrared hyperspectral imaging with imaging-type two-dimensional Fourier spectroscopy“, Kosuke Nogo, Kou Ikejima, Wei Qi, et al., DOI: 10.1039/D0AY01738H (Paper) Anal. Methods, 2021, 13, 647-659

The upshot is that when I condemned all plastic for this use, I was too hasty.  Avoid polyethylene, for sure.  But, assuming the glass choche works as I have described it, PETE plastic ought to work reasonably well.  Not as well as glass, but certainly not as poorly as polyethylene.

As an odd little footnote, Mylar plastic — the kind used to make space blankets — is the same stuff as PET/PETE plastic — polyethylene terephthalate.

Results

Below is a photo of a quart Ball jar (right) and the thick-walled PETE jar that I’m going to test.  That was as close as I could get to the same size and shape as the Ball jar.  FWIW, the PETE jar originally held salad dressing.  You can see that it’s much thicker than (e.g.) a typical disposable water bottle or soda bottle.

 

When I tested that last night — two temperature loggers on a raised garden bed, one covered with the PETE bottle, one un-covered — sure enough, PETE works pretty well.  But not as well as glass.

At the very coldest part of the night, the PETE jar provided between 4 and 6 degrees F of protection, or about half the maximum protection observed for the glass jar.

The lesson here is that when I condemned all plastics for use in frost protection, I was too hasty.  Polyethylene sheet is a terrible choice, from the standpoint of trapping long-wave infrared.  But PETE’s OK.  Not quite as good as glass, but pretty close.