Potatoes are an underappreciated garden crop, yet they’re easy to plant and care for. Spuds thrive in diverse soils and climates, offer a host of beneficial nutrients, and store well. Because store-bought potatoes are cheap, many gardeners opt not to grow them, but for those who do, deciding how to manage them can be a challenge. Garden resources are full of potato-growing ideas. The variety of options can be overwhelming, especially because each method has both proponents who report fantastic yields and detractors who spout stories of failure. To separate the wheat from the chaff, I organized a study to test the performance of five of the most popular potato-growing methods.
Potatoes are native to the Andes, where the Inca and their predecessors cultivated varieties in a complex environment: unpredictable El Niño-driven precipitation and starkly varied elevations with diverse ecosystems. Traditional cultivation involves digging trenches to create rows of soil and llama dung. A mix of seed potato varieties are buried with llama dung in the dug-up fill. This practice builds food security: Regardless of the season’s conditions, at least a few varieties will do well, even if others fail.
Western gardeners have adapted this approach into the trench-and-hill method. A 6-inch-deep trench is dug for each row of potatoes. Compost is worked into the bottom of the trench, and seed potatoes are planted at about a 1-foot interval, and then covered with mulch and soil. As they grow, the soil between the rows is mounded up around the emerging plant, creating hills to support the stalks and cover the tubers to prevent greening. At harvest time, gardeners use a spading fork and re-dig the trenches to turn up the new potatoes.
A more recent potato-growing method involves planting seed potatoes atop a surface of prepared soil, and covering them with compost and mulch. Some growers add a layer of newspaper or cardboard as a sheet mulch below straw or wood chip mulch. As the plant grows, more mulch is added around the stems in the same way as the trench-and-hill method. The difference comes at harvest time, when no digging is required: The mulch is pulled back and the tubers are plucked off the ground.
Other methods create a container for the plant. Bags, plastic buckets and totes, barrels, wooden boxes (called “towers”), and even stacked car tires have been used to grow potatoes on the ground, patios, and balconies. (Avoid tires, however, because they leach chemicals.) The idea is that, if it’s good to hill up around the plants, growers can bury plants over and over using containers with high sides, creating a deeper root structure and greater yield. This method is more flexible and easily used by those without access to soil they can trench. To harvest, the containers are tipped over and the spuds are collected. Some towers are designed to be harvested without killing the plant, with sides composed of horizontal boards that can be removed to access the roots without upsetting the plant.
Our test group consisted of 10 producers, ranging from farmers market growers to backyard gardeners, across southern Wisconsin (Zones 4b, 5a, and 5b). We tested five potato-growing methods to determine which one is the most productive and least labor-intensive for a small-scale grower. The first method was trench-and-hill, which we considered our “control” group. We also tested two surface-planting methods, straw mulch and straw mulch over newspaper; and two container methods, namely bags and wooden towers.
We kept other variables consistent. Each grower set aside five 8-by-8-foot beds in full sun. We planted 3 pounds of seed potatoes in each plot. Each plant received 3 quarts of organic compost (Purple Cow Organics Activated Compost, 0.7 – 0.3 – 0.3) at planting, and another quart while growing. Every plot was mulched with two rectangular straw bales and received the same amount of sun, rain, and attention. Throughout the growing season, growers noted the time worked on each method, and whether they weeded, watered, hilled up mulch, or picked Colorado potato beetles. At the end of the season, we harvested the plots, weighed and counted the yield, and totaled the labor time for each method.
In a word, our results were mixed. We looked not only at yield, but also at labor and cost. The results can be divided into “all data” and “uncompromised data.” Four participants had voles or standing water damage to some of their crops, which make their results difficult to interpret, but when taken together, the all-data statistics may be more indicative of real-world results. On the other hand, if voles and low-lying areas can be avoided, the uncompromised data may be what a gardener can expect. The most productive method was trench-and-hill. We received an average of 1.81 pounds of potatoes from each plant across all participants, but an average of 2.54 pounds from the plots not devoured by voles. The straw mulch, straw mulch over newspaper, and potato towers returned about 1/2 pound less per plant on average, whether from all participants or uncompromised ones. The bag containers were easily the lowest yielding, at just over 1 pound for all participants, and 1.7 pounds for those whose gardens were vole-free. All plants started with a seed potato weighing roughly 2.7 ounces, meaning even the lowest average yielding method returned a sevenfold increase, while the best plots returned more than 20 times the seed weight in edible taters.
Yield isn’t the whole story, though, as labor is as much of a gardener’s investment as the cost of seeds and materials. On a per-plant basis, all gardeners averaged the least time on the straw and straw-over-newspaper methods, at 8:39 and 7:42 minutes respectively. They spent 10:30 minutes on bags, 11:21 on trench-and-hill, and 16:59 on the towers because of the construction of the containers. Even though the trench-and-hill plots produced about 139 percent more than the two surface-planted methods, they took 140 percent more time. If we look at the uncompromised yields, the gap widens; gardeners spent almost 178 percent more time to grow only 130 percent more pounds of potatoes per plant in the trench-and-hill plots.
We can also break down the types of work and report the average number of times growers participated in that work per season for each method. We had plenty of rain in 2018, so most participants watered only once. Bags and towers required the least weeding, averaging 1.75 and 2.00 times respectively. The straw-mulched plots required a little more weeding than the straw-over-newspaper plots (2.25 vs. 2.13 times per season). The trench-and-hill plots required the most weeding, but not by much, at 2.88 times. On average, all plots were hilled up between 2.50 and 2.88 times, and cleared of pests (Colorado potato beetles or voles) between 1.50 and 1.75 times, which amounts to no real difference among the methods.
Finally, the methods varied in cost of materials. The trench-and-hill, straw, and straw-over-newspaper methods all cost $2.18 per plant. This includes a 2.7-ounce seed potato, 4 pounds of compost, and 11 percent of a straw bale for mulch. The bag container would’ve cost $3.18 — the additional dollar for the 50-pound grain bag — if we weren’t able to get the bags donated from the Wisconsin Brewing Company. The potato towers, though, cost $11.61 per plant; each tower held up to four plants. Although they received the same amount of seed potato, compost, and mulch, they also had frames built of lumber and screwed together, adding $9.21 to the baseline cost. And while one participant had strong yields from their tower, at 3.38 pounds per plant, most towers produced an average amount of potatoes when not inhabited by voles. Unlike the bags, the towers can be used for a few years, so this cost could be divided by two or three to amortize the lifetime cost.
We also measured other variables that didn’t seem to affect yield or labor. Our growers’ soils ranged from loam to clay, but their soil morphology had little effect on the yield or size of potatoes. We found that the average tuber size wasn’t greatly affected by soil type or method of planting: Trench-and-hill potatoes averaged 7 ounces each, while the surface plantings, bags, and towers hit 6 ounces. Other variables that played no discernible role included previous weed pressure, whether the bed was virgin soil or established, and the previous crop planted in the same location.
The Takeaway: Context Is Everything
We didn’t find that one method was the clear, overall winner. How someone chooses to grow potatoes comes down to their situation. Access to land, presence of pests, total yield required, cost, and labor considerations might point one grower toward bags, another toward surface planting, and another toward trench-and-hill. Our results fall into two categories: data-derived recommendations and anecdotal observations.
Our study results suggest three different potato methods, depending on a grower’s resources and goals. If a grower doesn’t have access to land but wants to grow potatoes on a patio or other outdoor surface, bags with compost and mulch are the clear winners over potato towers. A gardener can grow 16 potato plants in bags for the cost of every tower. Although bags had the lowest yield, they also took less time to plant and tend than towers.
If a grower has space to plant potatoes in the ground, the choice between using trench-and-hill or surface planting hinges on space, reliability, and the presence of voles. If space is at a premium, reliability is vital. If voles are present, the trench-and-hill method is best. It had the highest yield per plant and the most resistance to voles; only three of 10 participants had voles in the trench-and-hill plots, while only five of the 10 surface methods stayed vole-free. On the other hand, the trench-and-hill method required more work for each plant than sowing on the surface with newspaper and straw, and if voles and space aren’t an issue, this surface-planting method is the clear winner.
Trials often find results that weren’t in the original research design, and this experiment is no exception. Since I didn’t set out to test these observations, they’re offered as anecdotal suggestions, and would have to be validated in a controlled study. One participant had a wetter location than the others. The trench-and-hill plot suffered rot and severe crop loss, while the surface plantings had seemingly unaffected yields, likely because they were above the waterlogged surface. This result may hold for containers, but this participant also had vole issues that targeted the bags and towers, obscuring the result. Voles were the worst pest in our trial, although a few participants did have to hand-pick Colorado potato beetles. After harvesting plots in 10 locations, a pattern of vole damage appeared: Potato plots on the edge of gardens adjacent to lawns, forests, or bushes had most of the vole damage, while potato plots in the middle of gardens, with a “moat” of bare earth, seemed to fare better.
Optimizing Potato Plots
Participants in our study suggested a few ways to optimize the methods. One market grower plans to cultivate their potato bed; set seed potatoes on the surface; cover them with compost; and unroll a large, round straw bale over the plot, burying everything in 8 inches of straw. This may be an even more efficient method for large-scale surface planting. Another grower, who puts up hundreds of pounds of potatoes each year, uses cardboard and wood chips instead of newspaper and straw to cover potatoes. Although the voles attacked the trial potatoes, this grower’s adjacent crops with the cardboard and wood chips were vole-free. Another grower also used cardboard and wood chips between the rows and straw over the potatoes with similar results. In both cases, these plots were also largely weed-free.
For those who want to add to our body of data, we encourage you to read our more technical summary, view the complete data, and watch the video available at the Low Technology Institute.
This research was carried out for a grant from the U.S. Department of Agriculture’s Sustainable Agriculture Research & Education program (project No. FNC18-1128).
Scott A.J. Johnson runs the Low Technology Institute in the historic village of Cooksville, Wisconsin, where he lives with his wife, 6-month-old son, dog, nine chickens, and 120,000 bees.