By Will Bonsall
Considering that potatoes are the fourth biggest food crop grown by humans (after corn, wheat and rice), that they are so simple to grow, and so productive, it seems strange they aren’t more common in backyard gardens. I suppose it’s partly because, like the other staples, they are so cheap to buy, therefore not deemed worthy of the trouble or space. While non-organic potatoes are under a dollar per pound, organically grown spuds are significantly more — but are they worth it? Of course, I’m preaching to the choir here, but many do not realize or appreciate the difference between organic and conventionally grown — potatoes are more likely than most foods to take up and retain harmful chemicals from the soil. This alone goes a long way to justifying the price difference. That being said, many still feel they cannot afford to pay the difference, however justified, and that’s why we’re about to discuss growing your own, even if you only have a small backyard garden.
Yet another reason for growing your own is to enjoy the enormous range of diversity that is not available “off the shelf.” My brother’s Peruvian mother-in-law lived with us awhile and she was dismissive of the quality and selection of potatoes available to American shoppers. Accustomed to a dazzling array of colors, shapes and flavors back home, she considered the white-skinned, white-fleshed varieties sold here to be tasteless even compared to the white-on-white varieties cultivated in the Andean highlands. After years of growing hundreds of varieties in my Scatterseed Project collection, I’m inclined to agree with her. But again, the only remedy I see is to grow them yourself, so let’s go there now.
Potatoes are tubers, and tubers can form in different ways. Potato tubers form on the ends of runners, or stolons, which arise from the stem rather than the roots. This has important implications for how we cultivate them. The portion of stem that is underground is relatively small, unless we earth up (or hill up) the plants so that more of the stem is covered by soil. This not only encourages more stolon-forming and thus more tubers, but also protects the growing spuds from sunlight, which causes “greening.” The greening of potato skins is chlorophyl, which is quite harmless, in fact wholesome in itself. However, the presence of green skins indicates high levels of glycoalkaloids, which is decidedly un-wholesome.
It is mainly due to the need to hill plants that rows are spaced about 3 feet apart. The plants themselves don’t require that much; they could manage with half that distance if only we didn’t have to draw up earth around them. One way of doing this is the cute gimmick of growing potato plants in tires and adding soil (or compost) into them as more tires are stacked on, sometimes several high. There is a reason why this is a “cute gimmick” and not practiced on a large scale. For one thing, the water requirement of those soil columns is very great, and the space actually occupied is not much reduced; much of it is occupied by the tire itself (by the way, tires leaching chemicals unto the soil cannot be good). The real gain, if any, from this method is the three-dimensional increase in crop area by growing vertical, much like pole beans or trellised tomatoes. However, the difference is that one must bring in prodigious amounts of soil (from where?) to fill those rings. Growing potatoes in tires will always be a novelty unless you have a postage-stamp-size garden, but is there another way to minimize the space-wasting need to hill up plants? Some people grow potatoes in hay or straw (or even seaweed) mulch, adding mulch to a great depth to bury the stems and protect the forming spuds from sunlight. This enables us to set the plants twice as close, say, 14-18 inches in each direction. This approaches a no-till system, at least for that season. The spuds mostly form on the soil surface or within the mulch layers and thus are clean and easy to harvest (notice I didn’t say “dig”). Success assumes you have a way of controlling voles, which, in spite of my skunk, weasel and fox allies, I have not completely managed to do.
Of course, potatoes have enemies — don’t we all? — including various insects and diseases. Fortunately, disease problems are usually much less in small organic garden plots than in larger conventional plantings. While potatoes require moderate fertility, too much or the wrong kind can lead to health problems. For example, potatoes need abundant potassium and calcium, which could be provided by ashes and lime, which are both strongly alkaline. Alkaline soils (high pH) encourage scab, as does the use of fresh animal manure. Also, high levels of crude organic matter, especially high nitrogen, foster the growth of bacteria, which causes scurf on skins. Those black flaky patches aren’t particularly harmful, but they are unsightly and may necessitate peeling, which is otherwise best avoided. Well-aged compost, green manures and mulches can all add potassium, calcium and nitrogen in adequate amounts without causing alkaline soil. Late blight (the cause of the Irish potato famine) is best avoided by planting clean seed of resistant varieties.
Aphids can be a serious problem but are usually controllable by biological methods like beneficial predators. These include ladybugs and syrphid flies. The latter are encouraged by allowing parsnips and related plants (carrot family) to naturalize in the vicinity of the garden. Even if you don’t want or need any parsnip seed, the second-year flower heads provide a nectary for the tiny syrphids, not to mention other beneficial insects.
Colorado potato beetles are a particularly difficult pest, at least once they’ve discovered your patch (sometimes gardeners in new areas won’t see them for a few years, but it’s just a matter of time). There are several remedies of varying effectiveness. Hand-picking can be quite effective in small patches but can get old quickly. Growing spuds in deep mulch is very helpful but no panacea. Companion planting potatoes with bush beans is in my experience only partially effective — worth doing perhaps but not sufficient. It’s also reported to be mutually beneficial, in that potato plants allegedly repel Mexican bean beetles. Again, my own experience with this is encouraging but not conclusive. My cousin, Tom Vigue, tells me that a preventative spray of tansy extract is highly effective at repelling the beetles, but once they are established all bets are off. I’ve not tried this yet but Tom knows a thing or two, so hopefully I’ll try this next year.
In some years — depending on the looping jet streams — leafhoppers can be a serious issue, for which garlic spray is a useful repellent, even more important on fava beans.
Flea beetles are usually an issue for me only in early spring. I sometimes spray rhubarb leaf extract until the plants are better established, after which damage is minimal and sustainable.
Voles can do serious damage, but I’ve found that I can thwart them simply by timely harvest, i.e., as soon as the potatoes are fully mature. I tend to procrastinate on digging them, as that’s a very busy season and they seem to be holding their own. Maybe the spuds can wait, but the voles will not. Many a sizable spud would have been fine a week or two earlier before the rodents hollowed it out from the bottom, blithely unnoticed by me. By the way, the same applies to beets and to some extent carrots. Carpe diem!
One of my favorite potato rotations is with corn, either sweet corn or field corn. It works because of my corn-growing method. When hilling the corn in early July, I seed the whole piece down to ladino white clover. It makes a very modest growth in the shade of the corn (I also interplant soybeans in the corn rows), and after the corn harvest it flourishes a bit more before really cold weather shuts it down. In early spring the clover revives and makes yet more growth before I turn it in early in June or late May. Planting the potatoes in mid-June gives ample time for a splendid crop. For early potatoes, I plant them elsewhere. Which reminds me: There are few treats equal to a plate of boiled new potatoes, fresh-dug before fully mature with thinner-than-paper skins, for a flavor and texture that surpasses most anything.
Note: Certified organic producers should check with their certifier before using any pesticides (including pest repellents) not mentioned on their organic farm plan. When using pesticides on crops grown commercially and intended for human consumption, an applicator’s license may be required.
About the author: Will Bonsall lives in Industry, Maine, where he directs Scatterseed Project, a seed-saving enterprise. He is the author of “Will Bonsall’s Essential Guide to Radical Self-Reliant Gardening” (Chelsea Green, 2015). And indeed, he is also a distant cousin of another exemplary Maine horticulturist: Tom Vigue. You can contact Will at [email protected].
This article was originally published in the winter 2023-24 issue of The Maine Organic Farmer & Gardener.