The second part of the title is a joke. See below.
The first part of this post just verifies that you can, in fact, grow no-dig potatoes in leaf mulch.
The second part examines the astounding levels of internet-based bullshit manure regarding vegetable yields, and in particular, potato yields.
Edit, 7/12/2023: Near-total failure. Never going to do this again. See post G23-041. Edit 2/10/2024: If I had to guess why this failed (but an earlier try using straw bales worked fine), I think that the dark, compacted leaf mulch allowed the potato tubers to get too warm. That would explain every aspect of the harvest — few, small, knobby potatoes. Potatoes are a difficult crop at best in the South, due to high summer temperatures. Trying to grow them in Virginia, with just a thin, dark mulch covering the tubers — in hindsight, that was a bad idea.
No-dig potatoes using leaf mulch seems to be working just fine.
Above: My potatoes.
My no-dig leaf-mulch potatoes are coming up. Kind of.
Recall the back story. Last year I tracked down why some grocery store potatoes will sprout and grow in your garden, and others won’t (Post G22-004). Internet opinion seems roughly equally divided between “won’t work at all” and “works fine”. Turns out, there’s a good reason for that.
The key is to use organic potatoes. Non-organic potatoes are typically sprayed with a sprout inhibitor (chlorpropham reference) that permanently damages the potato’s ability to grow. Potatoes treated with that chemical won’t grow, or will grow poorly. Organic potatoes, by contrast, can’t use that, and so typically will sprout and grow just fine.
This year, I picked up three bags of organic potatoes from my local Whole Foods. Consistent with the theory, all three varieties sprouted when I chitted them.
So far, so good.
I planted them as no-dig potatoes on St. Patrick’s day, placing them on a weed-covered 8′ x 4′ raised bed and burying the whole mess in about a foot of leaf mulch. In terms of gardening effort and expense, it doesn’t get much better than that. Place potatoes on the ground and cover with mulch. I’ll probably have to put another layer of leaf mulch on there before harvest time, given how quickly the worms till that into the soil in a Virginia summer.
In Fairfax County, the leaf mulch is free for the taking (until it runs out every year). So this is a lot cheaper than covering them with straw (see Post #1073, on value-destroying gardening).
Based on at least one internet source, leaf mulch should work just fine for no-dig potatoes. That’s what they say.
Then I waited. It seems to take an eternity for the potato shoots to emerge. But in fact, with a deep no-dig bed like this, it takes about a month.
Somewhat oddly, the three “varieties” I planted (Grocery Store Gold, Red, and Russet) have three completely different growth habits. After six weeks in the bed, Gold is growing aggressively, the Red is just emerging, and the Russets are mostly still underground.
Plausibly, these are short-, intermediate, and main-season potatoes. Equally plausibly, I have no clue what I’m talking about. But the fact is, they’re all growing. So far, no-dig potatoes using free leaf much appears to be a winner.
Now, about that manure …
I admit that there are many, many things that I do not understand about potatoes. But I don’t think I’m alone. At the minimum, there seems to be a vast range of estimates for how many pounds of potatoes one can grow in a square foot of garden space.
To the extent that the high-end estimates seem to be pretty much pure manure.
For a variety of reasons, potatoes don’t like hot weather. But, to foreshadow the rest of this, there’s wide disagreement over how hot is too hot. In particular, if it gets too hot, they’ll stop setting new tubers. But the temperature at which new-tuber production stops is quoted in widely varying ways. It’s given as soil temperatures and/or nighttime air temperatures and/or daytime air temperatures ranging anywhere from 55F to 100F.
We agree that too much heat is bad. Heck if I can find agreement on what “too much” means.
In fact, the negative effects of high soil temperature leads some experts to suggest that you should not grow potatoes in containers (reference). At least, not in places with hot summers. Containers will allow the soil to heat faster, compared to growing potatoes in the ground or in raised beds. One controlled trial showed vastly better yields in raised beds than in any type of container (reference).
That said, in the table below, generally the “miracle” yields of 25 pounds of potatoes per square foot were claimed for some variety of “potato towers”, where you stack wooden frames to allow you to keep piling soil higher and higher around the potato plants. Near as I can tell, increasing yields by use of potato towers is pretty much 100% a myth, and makes no sense in light of how potatoes actually grow (reference).
Even if I ignored the “100 pounds in four square feet” claims, there seems to be a fair bit of disagreement on what a typical potato yield might be. I decided to tabulate the first 20 or so sources that I came across, to see how the results looked.
It’s not even clear what the right metric is. Some sources cite yield per pound of seed potatoes planted. Others variously cited pound or number of potatoes per plant, per linear row of plants, or per square foot planted to potatoes.
It is well-established that if you crowd potato plants together, you’ll get smaller potatoes. Crowding the plants results in more potatoes, but not necessarily more total edible weight of potatoes. Arguably, then, the most stable metric ought to be something like pounds of potatoes per square foot of garden or farm space.
Using that metric, and taking the median, the answer is that in a good year I ought to expect about 1.5 pounds of potatoes per square foot, or just under 50 pounds of usable potatoes from a 4′ x 8′ raised bed. With some sources weighing in well under that, and a few coming in well over that.
As a reality check on that, we need to consult The Martian. ” … In 62 square meters, I could grow maybe 150 kilograms of potatoes in 400 days … “. Converting that to U.S. units, a bit over 300 pounds of potatoes, in a bit over 600 square feet of space. He was constrained by starting from just 12 potatoes, so I assume that 150 kilograms is the final harvest, after growing several rounds of crops. If so, he was projecting yields of just a half-pound of potatoes per square foot, or firmly at the low end of the estimates above. But definitely in the ballpark of the data shown above.
If nothing else, that shows how ridiculously hard it would be to grow enough to feed myself, out of my back-yard garden. Potatoes are typically listed as producing among the highest yields of calories per square foot. But, at around 350 calories per pound, if I ate nothing but potatoes, and did the math right, to produce a needed 2500 calories per day, for the year, I’d need to plant over 1700 square feet of potatoes, or more than 50 raised beds of that size, growing potatoes or some other similarly calorie-dense food.
You will find internet sources that tell you can feed yourself for a year by growing vegetables in just 200 square feet of garden space. Clearly, those folks are using the same manure that routinely produces 100 pounds of potatoes in four square feet. In a potato tower, of course.
As a generally reality-based person, this little exercise in potato yields puts my vegetable garden into perspective. A few hundred square feet of beds is a hobby, not a serious source of food calories. If I really wanted to have a “survival garden”, I’d be thinking along the lines of thousands of square feet of garden beds, per person. Not a few raised beds.
If nothing else, that gives me more respect for the U.S. food supply. If I had to grow my own food, I’d surely starve to death.
