Ask the Expert: Mel Henninger on Organic Potatoes

Mel Henninger knows potatoes. Read what he has to say about his experience growing potatoes under organic conditions in an interview by Snyder Farm Intern Kate Brown. Learn about the best NJ varieties, must-have equipment, and cultural practices that produce quality potatoes your customers will love.

Dr. Mel Henninger and Farm Intern Kate Brown

Dr. Mel Henninger and Farm Intern Kate Brown

Kate Brown: Why do you know so much about potatoes?
Professor Mel Henninger: I was born and raised on a potato farm. I got my Bachelor’s at Penn State, then went on to get a Master’s and Ph.D. in Agronomy… in potatoes. My dissertation explored potato production management and the effect of storage treatments on potato chip color and reducing sugars. I did serve as a County Agent for a year before grad school. In 1972, I came to Rutgers to spearhead the potato cultural practices research and extension program for New Jersey. I retired in 2011 but I’m still here working on potatoes – as well as other vegetable and grain crops. It’s been said that I’ve devoted my life to the potato.

KB: What potato varieties would you suggest a beginning, small-farm grower try out?
MH: I can give you some names, but remember it’s best for growers to do their own on-farm variety trials to get to know what works best under their particular conditions. The success lies in finding a good source of seed and determining appropriate specialty varieties.

Approach variety decisions based on your intended market as well. If you’re looking to attract customers to a farm market, potatoes with unusual color or shape -exotics- are often considered. Be aware that some exotics tend to set a large amount of small-sized tubers. Also, exotic varieties tend to be long and become misshapen in higher temperatures.

Earlier varieties can help growers get a jump on profits. Some commercial early varieties include Dark Red Norland, a small red potato with white flesh, and Superior which is white-skinned and white fleshed. It is common to harvest potatoes early and sell them as “fingerlings” at market. Although farmers sacrifice full yield potential, they take advantage of better market prices from lower competition.

KB: Is there any equipment that’s a “must-have” when growing potatoes?
MH: The single most important piece of equipment is a harvester, aka digger. Even farmers who perform hand cultivation will experience grief without one. Although hand digging is necessary for small varieties, diggers are essential for larger varieties. The best way to get a harvester is to buy an old one another farmer is not using.

Though not as important as a digger, a seed piece cutter, like an old Trexler, is worth owning. Without a cutter, I might be able to cut 100 pounds an hour by hand using a sharp, thin bladed knife. With an old mechanical Trexler cutter, just myself and one helper could cut as much as 800-900 pounds per hour. Of course you need to properly orient the eyes to get the most out of the cutter.

Considering a planting rate of 1,700 to 2,000 pounds of seed pieces per acre, you can imagine how daunting hand cutting labor is even for small producers. My family used to start cutting just after Christmas, hand preparing seed pieces all winter long for spring planting. That’s a good reason to find an old Trexler and keep it in running order.

Early weed control with a spike harrow, spring tooth harrow or tine weeder is essential to minimize competition between potatoes and weeds. This should be done weekly following planting when the ground is still flat. Once the ground is ready to hill, shanks, plows, disks, or middle-busters are used.

KB: Can you give some tips for cultural practices that you’ve collected over the years about potato seed, nutrition, weed control, and harvesting?
SEED – Certified seed should definitely be used when available but it is important to understand what the certification signifies. The tests for certification ensure the particular seed pieces are true to variety and that viruses are not present. They are not screened for destructive fungal pathogens like late blight. More specifically, seed potatoes are visually inspected and laboratory tested to ensure that they are healthy and meet quality standards.

NUTRITION – A major difference between potatoes and other crops is the large uptake of nutrients required by potatoes in the beginning of the season. No matter what you do, you’ve got to start out with good soil. Potatoes do best when they follow in rotation with legume crops. Because the early availability of nutrients is essential, chicken manure should not be expected to contribute sufficiently. In my experience, even a large amendment of dried blood does not aid in potato development. Don’t expect leaf mulch to contribute to fertility in the year it’s laid down; leaves are a long term strategy to build soil quality and fertility.

WEED CONTROL – Early weed control with a spike harrow, spring tooth harrow or tine weeder is essential to minimize competition between potatoes and weeds. “Dragging-off” should be done weekly following planting when the ground is still flat. Once the ground is ready to hill, shanks, plows, disks, or middle-busters are used. Avoid burying emerged young potato vines during the second hilling since the young vines have exhausted seed piece reserves and will not re-emerge.

Under organic conditions, weed control is a tradeoff that substitutes tractor fuel for herbicides. The problem is, repeated tillage increases soil compaction, degrades tilth and hinders the crop. Some growers have tried black plastic but in our southern NJ coastal plains soils, that appears to negatively impact crop quality and quantity. Research on coastal plains soils using shredded leaf mulch does appear to improve crop quality and yield. I think it’s a worthwhile practice for organic operations to try since they don’t have the herbicide option.

HARVEST – Growing under organic conditions, harvest often takes place just after the potatoes have matured so vine desiccation is usually a non-issue. However, vines can be mowed up to two weeks before harvest to help control tuber size and to minimize the likelihood of tuber infections.

KB: Is there a down side to growing potatoes organically?
MH: The big problems experienced by all farmers of weed competition, disease, and insect pests become bigger problems growing under organic conditions since you have fewer options.

Be prepared to spend effort and time on cultivation, fungal disease treatment, and pest removal. If you have a dual conventional and organic operation using the same equipment, NOP standards require the washing of equipment before entering an organic field. That adds up to a lot of hours over the season.

The most common fungal problem in potatoes is late blight. In organic practice, labeled copper fungicides must be applied before disease is present in order to offer protection against late blight. Actually, organic growers really benefit from using our blightcast potato disease forecast updates to time their copper treatments. Start treating when the closest weather station report has accumulated 17 disease severity units (DSVs). The Blightcast Potato Disease Forecast updates and nearby weather station reports can be found at:

Copper is effective against early blight. If organic growers choose to utilize copper as a fungicide, it must be applied very often – starting when the plants are young – regardless of assumed threat. All plant leaves must be adequately covered to hopefully prevent fungal spores from germinating.

Colorado Potato Beetle, Leaf Hoppers, Cutworms, and Wireworms are the important insect pests in potato. Physically removing Colorado Potato Beetles is key since there are no effective insecticides available for organic producers.

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