|Greensprouted potatoes. Photo courtesy of New Brunswick Dept. of Agriculture and Aquaculture, www.gnb.ca/0029/00290048-e.asp
by Sue Smith-Heavenrich
Last spring I was intrigued when Andy Leed, an upstate New York grower, mentioned that he was “greensprouting” his potatoes. He’d been growing table-crop spuds for many years and, frustrated by the lack of organic seed tubers in smaller sizes, decided to diversify, planting part of his acreage to production of certified organic seed potatoes.
Leed prefers to plant whole seed tubers that are about the size of a golf ball, because he feels that they are less prone to disease and rot. He figured that greensprouting would give him faster plant emergence and an earlier yield of the smaller tuber size that is perfect for seed.
Greensprouting was originally developed for use with small, whole-seed tubers. Also called “chitting” or “pre-sprouting,” greensprouting involves exposing seed tubers to natural or artificial light in a warm environment before planting. This allows the development of short, strong, green sprouts and, if all goes well, a faster-growing plant.
“Greensprouting fits in well with the organic cultural practices I’ve already established,” Leed explains. “I tried greensprouting on a trial basis (in 2005) and decided this year to go ahead with the whole crop.” Part farmer, part curious naturalist, he kept notes on how his potatoes fared in the field, comparing plots planted with whole-seed tubers and those planted with cut seed.
In 2005 (a droughty year), “plots planted with whole-seed tubers grew well and produced a fair yield. Those planted in the traditional way, with cut seed, had spotty emergence. Dehydration may have been part of the reason.”
Advantages of Greensprouting
Leed believes that the extra labor involved in greensprouting will pay off in terms of earlier plant emergence and increased yield early in the season. Researchers have shown that greensprouting can hasten plant development and tuber initiation – a significant benefit when growing long-season cultivars in short-season climates. In one study,1 from 87 to 96% of greensprouted plants emerged by 18 days after planting, compared with 21 to 37% of non-sprouted seed. Non-sprouted tubers took about four to five days for their emergence rates to catch up. Even greensprouted tubers that were cut the day before planting emerged earlier than non-sprouted tubers.2
This is what Leed hopes to see on his farm: earlier emergence and earlier harvest. “A quicker emergence means less opportunity for seed to rot in the ground,” he notes. It also provides a leg up on potato diseases. “I’m hoping that by harvesting early we might avoid late blight,” Leed adds. This is critical if he plans to save his harvest for seed tubers.
Jim Gerritsen, who, with his family, cultivates nearly a dozen acres of potatoes at Wood Prairie Farm in Bridgewater, Maine, sprouts nearly 25,000 pounds of seed tubers each spring. He’s been greensprouting spuds since the early 1990s and has a solid 15 years of experience using this method.
“The advantages are most compelling,” he explains. “I gain about 10 to 14 days on the season.” Gerritsen finds he is able to grow late season varieties in the short season of Aroostook County. While the tubers are greensprouting, they’re safe from damage. The time and labor invested before planting means 10 to 14 days that the potatoes don’t have to be in the ground—and those days may mean the difference between avoiding blight or disease-bearing aphids, he points out, or avoiding the driest part of the summer.
Greensprouting also suppresses apical dominance, so secondary sprouts are encouraged to grow. Gerritsen sees more even sprouting in the field as well as higher tuber set with more tubers per hill. Though he’s producing certified organic seed tubers, he notes that a grower of table-crop potatoes would see a higher tuber set as well, and would realize a higher yield of properly sized tubers.
How to Sprout 25,000 Pounds of Seed Tubers
The goal of greensprouting is to get a few well-developed sprouts before planting into soil. This requires controlling light and temperature. When Gerritsen began greensprouting, he built about 900 wooden trays with slatted bottoms.
“They’re each about the size of a bread tray,” he notes, “and we fill them one to one-and-a-half tubers deep.” He made them stackable, with supports that allow gaps between trays to let light in. After filling the trays, he stacks them about 10 high, with three stacks per pallet.
Gerritsen begins greensprouting tubers in mid-April so that they’re ready to plant by mid-May. First he puts pallets laden with trays in a “hot room” (70 to 75 degrees F.) for a week to break dormancy. Then the potatoes need a “greening period” of cooler temperatures (about 50 degrees) with artificial or natural light.
“Potatoes are alive from the time you plant your seed to harvest, through storage, and as seed the following year.” Gerritsen emphasizes the need to treat tubers as living beings. As they begin sprouting, they are also respiring. If the temperature is too high, they lose energy due to increased respiration. If they’re stressed, they age earlier. The ideal is to have them in top vigor when they’re planted in the field.
Leed used a vacant greenhouse and began sprouting his seed tubers a month or so before planting. He layered seed two to three tubers deep in large slatted bread crates, bulb crates and shallow flats. Then he stacked the crates in the greenhouse, keeping the temperature near 60 degrees, and making sure light could reach all the seed tubers.
After a few weeks, each seed tuber had a few fleshy, greenish-purple sprouts that measured just over 1/2 inch – a bit long, compared with the 1/8- to 1/4-inch sprout length recommended in the literature, but they worked for Leed. After an additional few days of hardening off, the seed tubers filled the bins of his Checchi & Magli planter and were planted in the ground.
Instead of trays, some large-scale potato growers use net bags that hang on racks. Seed tubers are poured directly from storage crates into the bags, which are divided into sleeves to allow each tuber access to light. These bags are hung vertically on large racks that can be moved by forklift. When the tubers are ready to plant, the entire rack can be lifted onto a trailer and hauled to the field. The bottoms of the bags open so that seed tubers can be fed directly into hoppers of the planting machinery.
This is a pretty neat system, says Gerritsen, adding that if he were starting his potato operation now, he would opt for bags over crates – mostly because of the ease of handling large volumes of seed. The greensprouting season comes at the same time he’s filling tuber orders for other growers, making for longer-than-usual days.
Working Potatoes into a Rotation
Producing perfect organic seed tubers requires attention to details, such as a four-year rotation that Gerritsen uses that incorporates fungus-killing crops. The year following potatoes he plants spring wheat or oats. These he undersows with clover and timothy, which produce hay over the third year. In year four, Gerritsen plows down the hay and plants a smother crop of buckwheat followed immediately by ‘Dwarf Essex’ rapeseed.
Rapeseed is his “biofumigant,” as chemicals in it and other brassicas help kill the potato fungus Rhizoctonia that may be in the soil, and they may help suppress weed growth.3 Mustard is rated the best for this role, Gerritsen notes. But it’s an annual, and he’s concerned about weed seeds, especially in a wet summer like we saw last year, when he might not be able to get into the field to incorporate it into the soil in a timely manner.
Extra Time but Worth Trying
Though many European growers use greensprouting, it is not widely embraced on this continent. Given the extra labor, it’s no wonder it’s attracted a small following. Still, anything that can lengthen a season by two weeks and help reduce exposure to late blight and Rhizoctonia is worth trying. At least once.
1 Essah, S.Y.C,. and C.W. Honeycutt. (2004 ). “Tillage and seed-sprouting strategies to improve potato yield and quality in short season climates.” Amer. J. Potato Res. 81: 177 – 186.
2 Mikitzel, L., and D. Wattie. (2000). “Greensprouting seed tubers to improve early yield” (abstract). Amer. J. Potato Res. 77: 411
3 Suszkiw, J. (2004). “Mustard for pest control, not for your sandwich.” Agricultural Research 52 (10), www.ars.usda.gov/is/AR/archive/oct04/pest1004.htm?pf=1
Andy Leed, Starflower Farm, Candor, N.Y. (607) 659-3469.
Jim Gerritsen, Wood Prairie Farm, Bridgewater, Maine. (800) 829-9765, www.woodprairie.com.