This post is a classic example of why nobody consults this blog for gardening advice.
If you are a back-yard gardener, and are considering whether or not to grow potatoes, you want advice. Directions. You want somebody to say do this, do that. Follow this approach and success is guaranteed.
But much internet-based advice for the home gardener is folklore. Frequently repeated, never tested. Certainly not tested by the folks who repeat it. Such folklore is sometimes helpful, sometimes merely harmless, and sometimes dead wrong.
What I’m supposed to say in this post is something like “it’s time to chit potatoes now, before you plant them”. That is, get them to break dormancy and sprout first, then plant the sprouted potatoes. And then I’m supposed to explain how I go about doing that.
As if I were somehow privy to the innermost secrets of potato-chitting.
What I’m actually going to tell you is this:
- The evidence in favor of chitting potatoes is ambiguous.
- The recommended procedure for chitting potatoes is all over the map.
- Professional potato farms don’t chit their potatoes.
This year, I’m going to set up a little experiment to test the impact that chitting has, for my potatoes, here in Northern Virginia Zone 7.
But in this post, I’ll first explain how I go about growing potatoes in my back-yard garden. I ignore almost all the rules on proper potato etiquette. So it’s not clear what my advice is worth, anyway. But unlike your average garden blogger, I’m up-front about that.
Free advice is worth what you pay for it.
Here’s what I do
Even though potatoes are cheap, I grow them for a lot of reasons, but mostly because it’s easy and effective.
Deer won’t eat them. Neither, so far, will the bugs. In a good year, they produce a lot of calories per square foot. Within reason, you can harvest them whenever you’re ready. They keep well. They taste better than grocery-store potatoes. And around here, they’re done by mid-summer, and you can double-crop with beans or some other short-season crop. Last year, I planted late-season corn after my potatoes were done.
I start by buying organic potatoes from the grocery store. Organic, to avoid buying potatoes sprayed with a potent sprouting inhibitor (Post G22-004). From the grocery store, because I’m cheap, and it’s convenient, and so far, it works just fine.
There are some downsides to this. You have no clue what your varieties are. This year, mine are “red” and “gold”, per the picture above. If you live in the South, don’t bother with russets, as they take too long to mature for this climate (Post #G23-035). Other than knowing to avoid those, you have no idea if your grocery-store potatoes are early-season, mid-season, or main-season potatoes. (In the South, you would like to avoid long-season (main-season) potatoes, because potatoes don’t like Southern summer heat.) If you get a particularly good or bad crop, you can’t replicate the variety. And so on. Not to mention, no guarantee they are virus-free.
OTOH, given that I can typically get potatoes at the grocery store for around 80 cents a pound, as the price of seed potatoes, with shipping, approaches $10/pound, if you do this “right”, you have to have a pretty good yield, just to get your money back. It’s just a lot less stress to pick up a bag or two at the grocery store, than to obsess over which variety of ludicrously expensive seed potatoes to order.
I chit them near a window, at room temperature, starting on or about Groundhog Day. Just set them out, on a tray, and watch for sprouts to start. It’s less than totally decorative, but it’s close to no effort. This in USDA Zone 7, so adjust accordingly for your climate. This is roughly 10 weeks before the expected spring last frost date in this area.
See last section for discussion of chitting.
I plant on St. Patrick’s day, after cutting them into chunks the day before. St. Patrick’s, because I can remember the date. And because that’s about four weeks before our expected last frost date in the spring. Planted in the cold of March 17, it takes about a month for the shoots to emerge from the ground, so that, ideally, you’ll see those potato shoots just after danger of frost has passed.
Dig a little trench 4″ or so deep, chuck in the potatoes, cover them up, toss a little mulch on top. I aim for about a 1′ to 1.5′ spacing in all directions. Conventional wisdom says that if you plant them further apart, you’ll get fewer, larger potatoes. Makes sense, but I can’t say that I’ve tested that. You’re also supposed to “hill” them after they have grown a bit — just mound up a little more dirt onto the potato stems. Apparently the entire point of hilling is merely to keep the sun off the potatotes, so they do not form poisonous solanine (see Post G23-065, on why green potatoes can kill you, but green tomatoes won’t). Anything sufficiently opaque — dirt or mulch — will do.
That long time lag between planting and sprouting is a good reason to chit. If, somehow, your seed potatoes aren’t going to sprout, if you don’t chit, you’ll only find out about it a month or so after you planted them. Eventually — call it six weeks later — it will dawn on you that you aren’t seeing any potato sprouts, and you need to re-plant. Which, in the South, means you’ll end up trying to finish off your potatoes in the heat of summer, which is a bad idea.
I plant them in dirt. I’ve tried no-dig potatoes using straw (worked great, but straw bales are too expensive in my area, Post #1073), and no-dig potatoes using leaf mulch (dismal failure, but hey, the leaf mulch is free in my area, Post G23-041). Separately, for a variety of reasons, I’m not going to grow potatoes in containers. So dirt it is.
Why mess around with no-dig potatoes? Clay soil. Potatoes don’t like the heavy clay soils in my area, so it takes a huge amount of soil amendments (or bringing in topsoil, which I did for my raised beds) to get dirt that potatoes will grow well in. If you have clay soil, and want to try potatoes, do-dig is a lot less effort. In addition, you can use a year of no-dig to convert some lawn to garden bed, if you bury it deeply enough in mulch. Either way, in the right circumstances, no-dig is a way to reduce the total effort involved. (Also, the potatoes come out nice and clean.)
Why did no-dig potatoes in leaf mulch fail miserably, but no-dig potatoes in clean straw were a success? In hindsight, I think that it allowed the potato tubers to get too hot. I have since seen one excellent gardener (Self-Sufficient Me, on YouTube have a near-identical potato failure using no-dig in leaf mulch. Upon reflection, I think that the dark, compacted leaf mulch, in full sun, allows the potato tubers to get too hot, leading to few potatoes set, small potatoes, and knobby potatoes. Potatoes really do not like heat. If I do no-digs again, I’ll keep the soil temperature in mind, and either use deep, light-colored mulch, or set up a shade cloth over them.
Separately, regarding fertilizing potatoes, I dump enough leaves on the garden each year that I don’t have to worry about adequate soil nutrients such as nitrogen. But potatoes, in particular, are supposed to benefit from adequate potassium in the soil. It’s good for their skins. (And, correspondingly, potatoes in the skin are a high-potassium food.) It’s easy enough to test your soil for potassium with one of those $10 soil test kits from the hardware store, and if lacking, to spread minute amounts of potassium chemical fertilizers before you plant a potato bed.
Weed and water them, just like any other plant in the garden.
I pull off the flowers as they form. This, because the internet tells me to do so. This process aligns the potato plant’s chakras or something. I have no clue whether it makes any difference or not. Just FYI, potatoes have pretty white flowers.
I harvest them when the tops die back. Or I want the garden space for something else. Once they start laying lying down and looking straggly, that’s a good sign that they are done for the year, and can be dug up at my convenience.
Note, however, that potatoes do not like heat. In a warm-summer climate like Virginia, those tops are going to die back sometime around mid-July, no matter whether the tubers underground are finished or not. If I could pick my varieties, I’d grow early-season (short-season) potatoes. But given that I grow mine from grocery-store potatoes, … whatever happens, happens.
If I’m lucky, I’ll come in at the low end of the yields posted above. Not sure if it’s the climate, the soil, the gardener, or the lack of care. Just be aware that a lot of the miracle yield claims you’ll see on the internet are complete, total, and intentionally misleading bullshit. When in doubt, check with your local extension service to see what you can reasonably expect in your area.
Addendum: This year, a small controlled trial of chitting.
Why chit? Conventional wisdom says this will lengthen your growing season by perhaps a week or two (reference, University of Utah). I.e., put you a week or two head of the game, compared to planting without chitting. In the South, that’s a good thing, as potatoes don’t like heat, and they are going to die off in the heat of mid-summer, ready or not. Plausibly, you’ll get an extra week of growth before the heat kills off your potatoes, and that should translate into higher yield.
But, as with so much advice for the home gardener, everybody repeats this, and seemingly nobody tests it. There’s surprisingly little hard evidence on the benefits of chitting potatoes, and what evidence there is is mixed (per the Guardian newspaper).
If you search the internet, you’ll see disagreement on almost every aspect of chitting. The only thing I’m sure of is that it’s optional, because commercial growers don’t chit them. But seemingly experienced gardeners disagree on:
- Whether chitting makes any difference in yield, and if so, how much.
- Whether it makes more difference to early-season (short-time-to-harvest) or main-season (long-time-to-harvest) potatoes.
- Whether the potatoes should be kept cold or allowed to warm when being chitted.
- Whether chitting should be done in the light, or in the dark.
- Whether bags of commercial seed potatoes will “chit themselves”, that is, grow long fragile sprouts regardless (so that bringing them into the light, to produce short green sprouts, is preferred).
As a one-time professional user of vague, observational data, to me, this signals that the benefits of chitting, if any, are probably modest. If chitting had some huge benefit, people would have noticed.
In fact, I’d say there’s a case to be made that “chitting” was invented as a way to control the inevitable sprouting of potatoes in some climates, absent climate-controlled spaces. You’d bring your potatoes out of the root cellar, into the light, to green up the sprouts and control the rate of sprouting, so that they’d still be viable when planting time finally came around.
So this year, I’m going do to a little experiment. I’m taking half of each bag of potatoes, pictured above, and chitting them. And leaving the other half in the fridge for the next six weeks. This, now done, via the classic one-potato, two-potato randomization.
I then weighed the two randomly-assigned samples, and used a coin flip to determine which was to be chitted, and which was to be stored cold for the next six weeks.
I’ll be planting the chitted and un-chitted spuds, in more-or-less similar plots, on St. Patrick’s day this year. I’ll track their progress and, absent catastrophe, will weigh the final yield sometime mid-summer.
I realize there’s a lot of potential for random variation in this, despite my best effort to draw from the same batch of potatoes, randomize, and then plant as nearly identically as possible. I nevertheless think this can be informative. If, at the end of the season, I can barely tell the difference between the chitted and unchitted spuds, then I think that’s a pretty good clue that chitting has a relatively modest impact on yields. At least, in my climate, my garden, with my spuds, this year.
So, the null hypothesis is that chitting makes no difference. I’ll see if I can plausibly reject that. Expect results sometime around the 4th of July.
