Potatoes, Solanum tuberosum, like many of our favorite foods, have their roots in South America. Depending upon which source you read, they were domesticated in Peru as recently as 4,000 or as long as 7,000 years ago. The fact that they were a staple in the elevations of their native area gives us a clue as to the conditions they prefer – cool and not too wet. Originally, they were small tubers in various colors and shapes, and day length sensitive for the formation of tubers. Since they were from the tropical highlands, they were adapted to short days, and didn’t perform under the long days of European summers. But centuries of breeding and improving them has given us a wonderful nutritious crop that performs well in most of the U.S., is grown in all 50 states, and is available in many shapes, colors and flavors.

Potatoes, even though originally from this side of the Atlantic, actually came to this country from Europe. The early explorers had an inkling of the food potential of those funny looking tubers and took them back home to Europe sometime in the middle 1500s. Although it took time to improve the varieties to perform in the quite different European climate, it wasn’t long before they were being included in the diet. They kept well, so were included on ships making long voyages, and soon the sailors noticed that those who ate potatoes didn’t suffer as much from scurvy (there is much vitamin C in those spuds; in fact, it’s the main source of C in many American diets.) They were introduced here in the 1600s but weren’t widely grown for at least another century.

Like most of our vegetable crops, potatoes want a balanced soil and a pH of around 6.0. Because the saleable portion grows under the soil, a deep, loose soil is preferred, but most soils will work as long as they are well drained. Conventional fertilizer recommendations are for 160 to 200 pounds of N per acre. Verlin Rockey of Milk Ranch Specialty Potatoes in Colorado told us he uses 3 tons of compost per acre (made with equal parts turkey manure, feedlot manure, straw and sawdust) for his certified organic potatoes. Many growers turn under a green manure cover crop or apply animal manure the fall before planting potatoes as well. Just don’t apply raw manure right before planting them. Besides being a possible source of bacterial contamination, it can make the incidence of scab much greater.

There are several significant insect pests that can affect your yield – including aphids, flea beetles, leaf hoppers and Colorado potato beetles (CPB). Although flea beetles can make the leaves look bad early in the season, the infamous CPB can take plants down to bare stems fairly rapidly. Both adults and larvae eat the plant. We start watching for the clusters of bright, orangey-yellow eggs as soon as the leaves break the soil surface. We start control by crushing those egg clusters, but it’s a measure that wouldn’t work on a larger planting. Two strains of Bacillus thuringiensis (B.t. var. san diego and B.t. var. tenebrionis) are effective on this insect, but must be timed correctly. It is only effective on the first two instar larval stages, so as soon as we start seeing the larva hatch, it’s time to spray. Be aware, however, that as far as we can tell, there is not an OMRI certified version of this Bt and if you are certified organic, you’ll need to take other measures such as botanical insecticides. Finally, if you have bats flying around, they may be helping you more than you know. We’ve been told about piles of the wings of CPB in bat roosts, so it pays to encourage those tiny mammals.

Mice can also be a significant pest. We find that they do a fair amount of damage to mature tubers in the time between the foliage dying back, and digging. We could manage this by digging sooner and storing them, but we lack a proper storage facility and they keep better for us in the soil until really cold weather. Deep organic mulch can exacerbate this problem by giving them a place to hide.

Potatoes are a member of the nightshade family, along with the familiar and popular tomatoes, peppers and eggplant, as well as some lesser-known food crops. There are also several common weeds in the family such as black nightshade, jimson weed and bull nettle. Tobacco, nicotiana and even petunias belong also. All this information is to introduce the idea that crop rotation, ideally three years between crops in the same family, can be an interesting exercise if your cropland is limited. But rotation is one necessary tool to help combat the diseases that can threaten your potato crop.

As with most of our vegetable crops, the list of diseases you might see is daunting: early blight, late blight, scab, blackleg, leaf roll and mosaic viruses, rhizoctonia, verticillium wilt, and several rots. All will affect your yield, but some, like late blight (Phytophthora infestans) can ruin the entire crop – it caused the Great Famine in Ireland in the 1840s. Since the Irish depended on the potato for the bulk of their diet, when the crops failed, a million or more starved. Although fungicides will control many diseases, the best “controls” are healthy soil, good crop rotation and having disease-free seedstock.

Weeds and water
Weed control is important for good yields. There are several ways to manage weeds. A lot of farmers use a deep organic mulch. This has the added advantage of keeping the soil cooler. Many growers use cultivation: once as soon as they can see the row, and one or two “hillings”. “Hilling” potatoes – throwing soil over the row, not quite covering the plants – covers emerging weeds and gives the tubers more room to grow. There is also some use of plastic. Although it is effective in controlling weeds, black plastic can make soil temperatures high in warmer climates, and the plastic can be difficult to remove before digging when done on a small scale.

Potatoes need consistent moisture for best yields. This means the ability to irrigate if necessary. They are most “needy” when the tubers are bulking. Here in the humid southeast, we use drip irrigation. It saves water and keeps moisture off the leaves – staving off fungal diseases. However, whatever method you are using for your other vegetable crops will also work for potatoes.

One of the best ways to have great yields and fewer disease problems is to use disease-free seedstock. Since potatoes are generally produced vegetatively, cutting the seed potato into 1- to 2-ounce pieces and planting the pieces, whatever disease organisms are in the seed are planted right along with it. The process of producing the certified seed potatoes is one we had never thought much about. However, Verlin Rockey made the whole interesting process come alive.

It starts in the lab where the producer takes a few cells from the meristem tip of the parent plant. The plant is chosen because it is healthy and a good representative of the characteristics of the particular variety. Those cells are cultured in a test tube, increasing by a factor of five every two weeks. When there are enough plantlets, they are taken from the flask, planted in flats, and grown in the greenhouse. They produce small tubers in the flats. The next planting season, those small tubers are planted in the field to produce full-size seed potatoes. Several times in the process, the plants are tested for disease, and rogued out. Seed potatoes are marked on the label as to how many generations the seed is from the lab – how many years grown in the field. Each state that certifies seed potatoes has its descriptors. This link has a chart identifying them: http://www.umaine.edu/paa/Certification/ltdgencht2004.htm
What does the generation matter? Well, diseases, especially those caused by viruses, tend to build up in potatoes each year. In years past, before we understood viruses (or could see them under a microscope), a potato variety was said to “run out” and the only way to combat it was to breed new varieties from seed and rogue plants displaying symptoms. Now, with tissue culture and anti-viral methods, a variety can be “cleaned-up”. So, while we can continue to use saved potatoes as seedstock, eventually viral disease will affect our yields – by as much as 50%. By going back to certified seed every few years, we can avoid that yield drop. Mr. Rockey suggests purchasing generation 4 seed and keeping it to generation 6, then going back to certified seed.

Varieties
There are so many varieties of potatoes we hardly know where to begin. A lot of variety selection has to begin with your market. What does your market want, what is everyone else growing and what do you think you can sell? We tend to grow what everyone else isn’t growing. Mostly because we have limited space and want to “stand out” in the market rather than sell tons of potatoes. For ourselves, we love Kennebec, an old, multi-purpose variety that keeps well, and Carola, a yellow-fleshed variety. We just tried a new variety – Colorado Rose – that Paul thinks is the best he has ever eaten. We’re growing it and Carola in the high tunnel this year. However, you can have blue skin with blue or white flesh, red skin ditto, buff skin with white or yellow, round, long or fingerling shapes, moist, dry or waxy flesh. There are a LOT of choices. Looking at a specialty potato catalog is like being in a candy store – hard to choose. However, not all varieties will do equally well in all situations, so if you are trying some new ones, you might want to keep the planting small the first year and evaluate them for their profitability. And don’t forget creative marketing – how about having red, white and blue potatoes for your customers’ Fourth of July potato salads?

A couple of last thoughts on variety selection. There is at least one GMO variety called “New Leaf”. It was engineered as a Bt variety to combat CPB, but has been quietly “mothballed” by Monsanto. And, there is a new variety bred to be grown in Florida, where the heat makes growing potatoes difficult, that has been found to have 1/3 fewer carbohydrates – a boon to carb watchers. It is a 65-75 day variety and should be available to consumers in January. We couldn’t find a variety name, but if it’s a hit, we’re sure the seed producers will eventually have it.

Resources
Want to try potatoes as a larger part of your offering? This site at Penn State has some good costing information. It’s based on conventional production, but is easy to convert:
http://agalternatives.aers.psu.edu/crops/potato/PotatoProduction.pdf

Looking for some absolutely fabulous varieties to try? Here are a few sites to get you started. For us, they make us want to grow many more potatoes that we have room for.
http://www.milkranch.com/
http://www.woodprairie.com/
http://www.ronnigers.com/

All of them have great growing instructions and mouth-watering pictures. It’s almost potato planting time. We’ll be putting a few in the high tunnel about the middle of January. Enjoy growing (and eating) the nutritious potato.

Alison and Paul Wiediger have 2.5 acres of vegetables, 8500 square feet of high tunnels and a greenhouse operation in Edmonson County, Kentucky. They write about vegetables six times a year in GFM.