Post #1073: No-dig potatoes as value-destroying gardening.

Posted on March 24, 2021

I grew potatoes for the first time last year.  Just a 4′ x 4′ test plot in a little raised bed filled with loose soil, essentially Mel’s Mix ™.

Based on that small trial, I’m sold.  Almost no work, almost no pests.  Great yield of calories per square foot.  Keeps well.

And tastes good.  Fresh potatoes taste better than potatoes that have been sitting around for a year.  Who would have guessed?

I now want to scale that up to a much larger garden plot at the back of my yard.

Problem is, this being Virginia, the soil is clay.  The tilth has been improved over the years by piling random organic matter on it.  But its still far too heavy for growing potatoes.

As a low-effort gardener, and out-of-shape from pandemic sloth to boot, I am not looking forward to trying to break up that soil.  Certainly not a couple-hundred square feet of it.

Enter the no-dig method for growing potatoes.  This is often synonymous with the Ruth Stout method, for the gardener who invented (or at least popularized) the idea of growing vegetables in beds mulched with a thick layer of hay.  The advantage is that the vegetables grow well and you don’t have to till or otherwise disturb the soil.

You can find any number of guides for doing no-dig potatoes.  They all boil down to planting the potatoes either on the ground or in a shallow trench, covering with about a half-foot of hay (well, ideally, straw), then forgetting about them until it’s time to harvest them.

I have to say, the last part sounds appealing.  And in general, the reputation for this method is that it’s easy to do and provides yields that are nearly equivalent to growing potatoes in the ground.  And it gives you clean potatoes, as they form in the mulch, not in the ground.

So, what’s the catch?  What’s not to like about a low-effort high-yield gardening method?

A bale of straw is $13, and that ain’t hay.

Turns out, around here at least, it’s the cost.

I went looking for straw bales in the pricey Northern Virginia suburbs.  (Straw rather than hay to avoid sprouting whatever seeds might be in hay).  And just about choked at the prices.  My local garden store will sell me straw for about US$13/bale.  If I want to make a 40-mile round trip, I can find them at my nearest Southern States co-op (Manassas, VA) for about US$8/bale.  And if I want to travel even further and play the Craig’s List lottery, I could probably find them for modestly less than that.

Ironically, “hay” is used as the epitome of something cheap, in the quaint idiomatic expression “that ain’t hay”.  “That ain’t hay” means “that’s a significant sum of money.”  (Apparently this is a purely U.S. usage, as Google finds no reference to it in Canada, the U.K., or Australia.)

A typical U.S. square bale is 12″ x 16″ x 48″, or just over five cubic feet of hay or straw.  Given that I’m supposed to mulch the bed to a depth of half a foot, at first blush, one bale will cover about 10 square feet of garden.  It will be more than that, as the hay decompresses a bit when spread out.  But I don’t think it’ll be vastly more.

Given how few bales I can fit into my car, I’m going to buy them locally.  And so, roughly speaking, the straw to cover my no-dig potato plot will cost me $1.30 per square foot. 

As an economist, I have to ask:  Is the market value of the straw greater than the market value of the resulting potatoes?  Is this a “value destroying enterprise”, in the sense that the cost of the raw materials exceeds the value of the finished product?

And I’m afraid that the answer is, yes, it probably is.  Typical commercial potato yields are quoted at about a half-pound per square foot.  (Rutgers University (.pdf), or  calculated from Virginia Tech (.pdf)).  Typical home garden yields seem to run from half-a-pound to a pound per square foot (calculated from this reference, or calculated from this reference).  That seems a little less than I think I got from my little plot last year.  But if so, not hugely so.

Right now, I can walk into my local grocery and buy 10 pound bags of perfect Russet potatoes for about $0.60 per pound.

And so, my initial conclusion is that, at the prices I have to pay, this approach takes about $1.30 worth of straw and converts it to about $0.60 worth of potatoes.  Add in any other costs (cost of seed potatoes, cost of any soil amendments) and that just strengthens the conclusion that this is probably a value-destroying enterprise.

Caveats, and why I’m going to do this anyway

Can I justify this by saying that the straw will last for years?  Probably not.  In some climates that may be true.  But in the hot, humid summers of Virginia, my experience is that any sort of leaf mulch pretty much disappears over the course of a summer.  To the contrary, I’m guessing that I might have to beef up the straw mulch depending on the length of the potato growing season.

Can I find cheaper commercial mulches that might work?  Maybe.  Around here, the County gives away shredded hardwood mulch and shredded leaf mulch.  All you have to do is pick it up.  I’ve done that, and while the product is fine, the shoveling is not.  It’s just a lot of work to get it to where you want it.  (Certainly compared to picking up and placing a straw bale.)  Commercial bagged shredded hardwood much can be had for about $7.50 for five cubic feet.  Unlike the leaf mulch, the hardwood mulch will last several seasons.

By the time summer rolls around, I can add grass clippings from my lawn.  So I will have some source of cheap mulch later in the year.  But nothing on-hand to get the beds started.

Am I being vastly too pessimistic about how many square feet a straw bale will cover?  I don’t think so.  You have to have it packed tightly enough so that no light penetrates, else you end up with green potatoes.  I might have been somewhat pessimistic, but I don’t think I’m off by a factor of more than two, which is what it would take to bring this up to break-even.

Can I eke out that precious straw some other way?  No, seriously?  I’m going to fancy this up, add a lot of fuss and labor, to conserve straw?  I’m cheap, but I’m not that cheap.

I’m going to do this anyway.  Fact is, I garden mostly for the entertainment.  So I’m going to give this a try, using a few $13 straw bales from the local garden center.  But also giving it a try with some $7.50/bale-equivalent bags of shredded hardwood mulch, which is not only cheaper, but should last longer.

I can’t justify it, economically, as a method of food production.  But as food production plus entertainment, it’s not that bad a deal.  So I’m going to give it a try.