In which we reveal the results of 2022's Annual Potato Experiment, propose a conclusive and holistic theory on potato hilling, and hopefully drive a stake through the heart of potato towers. With references and primary sources, of course!

If you’ve spent five minutes googling how to grow potatoes, you’ll be familiar with the concept of “hilling” which is the act of piling dirt around young potato vines as they come up, leaving only about 6” of green vine exposed, and repeating that as the vine grows more.

It’s a simple, straightforward action, but the commonly-held reasons to do it are unresolved, conflicting, and occasionally imaginary (similar to claims of “liver cleanses” and lemon juice turning your blood alkaline).

According to the internet, hilling is done because –

  A) It forces more potatoes to grow in the hill, and so if you keep hilling indefinitely you can indefinitely stimulate more tubers. The end result of this chain of thought is that a potato tower will let you produce like 800 potatoes from a single vine.

and/or –

   B) The extra soil prevents the growing tubers from getting exposed to sunlight and turning green. Green is, generally speaking, bad on potatoes. (But also don’t freak out about green potatoes, more on that later.)

Reason (A) is the meme perspective.

Reason (B) is the professional-ish agricultural perspective.

Guess which is true?

HA! It’s a trick question!

(A) is half right and half wrong, while (B) is accurate (sunlight = green ≈ solanine), but it also misses the other reasons to hill beyond simply avoiding green, so you might say it’s “half-right.”

Hilling to Make More Potatoes

The myth that hilling stimulates new tuber growth seems to be a case of cart-before-the-horse, combined with unawareness that potatoes come in determinate and indeterminate varieties, similar to their nightshade cousin, the tomato, but with different characteristics. I also believed in the myth when I first read it years ago but real-life experience and research changed that. Let me save you time.

When you look closer – the level of misinformation about hilling that gets repeated by seemingly legit, trustworthy sources is comedy. It’s a doorway into the matrix, where people are living in an alternate potato tower reality, reinforced with doctored pics and newbies with blogs and YouTube and unearned authority.

Total Imaginary Bullshit

It’s not as if world hunger could be defeated with 80-foot potato towers but in 7,000 years of cultivating potatoes no one ever thought of it before Reddit and Bored Panda existed. And of course, just like the liver cleanse myth, there are plenty of companies willing to take your money while propagating the fiction.

I came across this fantastic analysis of the entire phenomenon of potato towers, from biological to societal, complete with google trends graphs tracking how they myth spread through the internet. Check out Cultivariable, it’s great. I have nothing more to add on the subject, and considering how thorough that piece is, neither does anyone else ever again.

Hilling to Keep Potatoes From Turning Green

Certainly blocking sunlight does keep potatoes from greening. But if it was the prime reason for hilling then it would make sense to hill later in the season, when potatoes actually exist and not when the young vines are just sprouting. And I’ve noticed that if done a little sloppily (ahem) hilling can actually increase the likelihood that top level tubers may get exposed. The overarching reason to hill is to increase the general MARKETABILITY of potatoes, for large growers, by adding an extra layer of defense against disease and insects.

For the 2022 growing season, I hilled half my potatoes and left the other half unhilled.

Observations of the experiment:

  • Hilling makes the vines more vigorous, which in turn boosts the size of the potatoes and perhaps to a small extent, the net number of potatoes. Stronger, fuller vines mean more energy.
  • Besides being more robust, my hilled vines flowered while the unhilled vines did not. Which surprised me because due to my having always hilled potatoes since I started growing them, I’d never had a plant that did NOT flower, until the one time I skipped it. It is said that flowers indicate the development of tubers underground, and while there were still potatoes on the non-flowering plants, they did seem less compared to the hilled.

Burlap bags to block the searing afternoon summer sun. Notice the difference in vines between hilled & unhilled.

* * *

Whether hilling will stimulate a second layer of potatoes beyond the first growth from the seed potato depends also on whether the plant is “determinate” or “indeterminate.” Kind of similar to tomatoes, the potato relative, but to a more pronounced degree in tomatoes.

For Tomatoes:

Determinate = they reach fruiting and stop.

Indeterminate = as long as environmental conditions remain stable – mostly the temp above 60F – they will keep producing fruit. (for about two years, anyway, everything alive has an expiration date)

Indeterminate tomato plants also benefit from ongoing pruning.

(Sidenote – the world record for most fruits from a single tomato plant is held by the “tomato tree” which interestingly, lives at Disney’s Epcot Center in Florida! Over 32,000 in a single year!!! )

One of the tricks passed on to me by Bianka is to plant your tomato starts quite deep, as in 3/4 underground. I can confirm, it allows you to get tomatoes established earlier in the year and compels the plant to double-up its root system.  

For Potatoes:

Determinate = they produce tubers laterally, on the same level with the seed potato

Indeterminate = they produce tubers up the subterranean stalk, up to about 12” above the seed potato. Thus – you hill indeterminate so those topmost tubers don’t get sunlight. And I think it’s reasonable to assume you also provide some amount of stimulation to the vine.

I’ve noticed that determinate/indeterminate notation with seed potatoes is often ignored by sellers. I personally keep this handy, comprehensive list of my phone. He also has one of the clearest, and true, explanations of D/I Potatoes. (Although he does carelessly give an air of authority to the notion of potato bags / towers.)

* * *

I find potatoes to be one of the most interesting plants, they’re like hyper-adaptors of sorts. Take a potato from your cabinet that is sprouting white tendrils. If you bury that potato but keep some of the sprouts above the ground, they will rapidly morph into leafy green potato vines, while the ones underground will stay pale white and become roots or tubers.   This is my new system, using up the last remaining sprouted winter-stored potatoes. It’s a fun jumpstart instead of waiting for those first little potato sprouts to come up. (When they first peek above the soil, young potato vines look like little green roses.)

I’ve tested out multiple varieties, and so far, my favorite is Russet Burbank, which unsurprisingly is also the most popular potato in the US. Why? It’s large, it’s productive, it stores quite well, being slow to sprout and remaining firm the longest.

My palate is unrefined so honestly, I couldn’t really notice any difference in taste between varieties. Those garden catalogs and signs at Portland Nursery really talk it up poetically. The distinctions I notice are more about the texture of the flesh, how tough the skin is, yields, and storage differences. Certainly degrees of disease resistance.

Growing and storing multiple varieties, it was unexpectedly interesting to see the wildly different way they sprout during 6-8 months of storage in the basement – vigorously and stringy, slow and compact, etc. As well as how soon / late they start getting soft.

Here’s a good example of the difference between storage qualities of potatoes. Huckleberry Gold on the left, Russet Burbank on the right.  Potatoes harvested September 12, pic snapped January 29 – almost 5 months in the basement.



How to Store Potatoes

I’ve tried several methods, and the simplest seems to be the best. Many gardening blogs will advise you to layer the potatoes in straw, and keep them cool, dry and dark. I did that a couple years but the basement is damp no matter what and I found that the straw would gather moisture over time and promote fungus.  There might be a rotting potato somewhere in the middle of your straw vault and you won’t know it.  

How do I store them now? My preferred method is the easiest – just put them in a cardboard box, not touching, and close it loosely. I like to put 3 flaps down and leave one open for air circulation, and stack the boxes of potatoes angled to each other so there’s no sagging onto the lower box. Since you just want a single layer, shallow boxes work best.  And unlike straw, you can instantly see any rotting potatoes.  

And if you don’t know, at harvest you want to just lightly brush off the dirt which will serve as an additional layer of protection. Then let the potatoes “cure” – i.e., dry out and let the skins toughen up. When they first come out of the ground the skins are pretty soft so take care because any nicks will lead to spoilage later in the storage period.

When you pull up the potato plants there will inevitably be many sizes of potatoes from large to small and still developing. I like to use the small ones first, using them whole for stews and whatever, and save the larger ones for baking. Towards the end of winter, with so many soft potatoes (still perfectly edible, don’t be a wuss!) means plenty of mashers.

Oh! And the other thing small-to-medium potatoes are great for making is Syracuse Salt Potatoes. Seriously – I can’t believe how friggin’ good and simple they are to make. Read the background on the dish, which is fascinating, on Atlas Obscura, and use the “recipe,” such as it is, here. Biting into a grape-sized Syracuse salt potato, dripping with melted butter is just amazing…. Crisp and salty and buttery and uniquely fluffy inside… Don’t use potatoes any bigger than the bottom end of a pint glass because they won’t cook through properly or get the angelic texture. (You use your familiar size references, I’ll use mine, don’t judge.)


* * *

Yeah, So What’s With Green Potatoes?

The green color in potatoes is chlorophyll, stimulated by sunlight, and is not toxic in itself. The undetectable toxin you want to avoid is solanine which develops in the same tissues along with chlorophyll, but it’s not a 1:1 ratio nor guaranteed to develop at all. Being pretty lazy, I often leave curing potatoes outside (NOT in direct sunlight of course) and they’ll start getting a bit green…

The amount of solanine a human would need to consume to reach a serious, substantial effect is extraordinarily high. The real-life symptoms of solanine consumption are likely to be much milder, like 24-hours of gastrointestinal distress (solanine makes intestinal walls less permeable) and not permanent.

Symptoms include nausea, diarrhea, vomiting, stomach cramps, burning of the throat, heart arrhythmia, headache, and dizziness. Hallucinations, loss of sensation, paralysis, fever, jaundice, dilated pupils, and hypothermia have been reported in more severe cases.

It is suggested that doses of 200–400 mg for adult humans can cause toxic symptoms (20–40 mg for children). Most commercial potatoes have a solanine content of less than 0.2 mg g−1.141 However, potatoes that have been exposed to light and have started to turn green can show higher concentrations.”

The chemical measurements of solanine concentration in the green will vary, but even at 100x the solanine of a non-green potato, it’s clear that you would have to eat many dozens, if not more than a hundred, very green potatoes to experience significant solanine poisoning. Also, solanine is concentrated mainly in the skin, so just peel them, eh?


# # #

Leave a Reply

Your email address will not be published. Required fields are marked *