If you want to grow epic potatoes, there is no one better to learn from than Jim Gerritsen, the founder of Wood Prairie Family Farm in Bridgewater, Maine. Jim has more than 45 years of experience growing potatoes organically, and he came on the podcast to share everything you need to know to have a successful harvest, from how to prepare the seed potatoes and soil to how to store tubers so they’ll last for months on end.
Jim is a third-generation farmer who started Wood Prairie Family Farm in Northern Maine when he was 21 years old, and in recent years, he passed the baton to his son, Caleb. The farm is 115 acres and has been certified USDA organic since 2002. It also has the Maine Seed Potato Certification Program’s seal of approval, meaning it can sell seed potatoes — the little tubers that farmers and gardeners alike plant to grow a new crop of potatoes — that are state certified to be free of disease and damage.
Maine was the No. 1 potato-producing state in the country about 70 years ago, and Aroostook County, where Wood Prairie Family Farm is located, was the center of the “potato empire,” Jim says. Potatoes have been grown in the area since the first European settlers arrived, and today Maine continues to be the national leader in growing seed potatoes.
This week’s encore presentation of my conversation with Jim from 2021 is very timely, as potato planting time is nearing. For a detailed write-up of everything we discussed, with photos, see the show notes from the original broadcast.
While you’re here, I want to take a moment to remind you that I have a new book out, “The Vegetable Gardening Book: Your complete guide to growing an edible organic garden from seed to harvest.” It’s chock full of insider tips and new-to-you information that will help you step up your gardening game and tackle challenges.
And on tap for this spring is my new Online Gardening Academy™ premium course, Organic Vegetable Gardening. Sign up for the waitlist here.
Why Choose Organic Seed Potatoes
Conventionally grown seed potatoes have been treated with fungicide and systemic insecticide and given synthetic fertilizer. But an organic seed potato hasn’t been treated with chemicals, and that means it’s a case of “survival of the fittest” Jim says. Therefore, organic seed potatoes are resilient, with more vigor and better disease resistance. In good soil, organic seed potatoes will grow into healthy plants that don’t need chemical pesticides and fertilizers, and the tubers will be more nutrient dense.
Why Maine Is a Great Place to Grow Epic Potatoes
Two things that make Maine a great place for growing potatoes, Jim says: the climate and the soil.
Maine benefits from being far north, where it doesn’t get all that hot in the summertime, he says. It also has a good distribution of rainfall, cool nights and sunny, warm days. And the soil is sandy and well-drained.
Potatoes are a cool-season crop with shorter growing seasons to the south. But up north in Maine, potatoes can grow through summer and can be harvested in late September and October.
The Difference Between Seed Potatoes and New Potatoes
To make seed potatoes, farmers kill the top growth of potato plants before the tubers have grown to full size. They are left in the ground for a few weeks so the moisture content in the skin will decrease. This toughens up the tubers so they can stand up to the rigors of mechanical harvesting and long-term storage.
“New potatoes” were harvested while the plants still had green foliage, which has not been killed, cut or removed. The tubers are immature and tender, with skins that can be rubbed off with a thumb. Having access to true new potatoes is one of the advantages of growing potatoes at home.
In Year in the Life of a Seed Potato Farmer
The growing cycle of seed potatoes in Northern Maine starts in mid-April. It takes about a month to warm up the tubers for planting, so that’s when Wood Prairie Family Farm takes out about 25,000 or 30,000 pounds of seed potatoes to “green sprout.”
When the weather has dried out and the soil is 50 degrees at 7 a.m. at a depth of 4 inches, the conditions are right for planting. This is usually May 15-18. It then takes a few weeks to get everything planted, wrapping up in early June.
In August, crews “kill down” the fields. Organic farmers use propane torches to kill the top growth of the plants, or they can use mechanical beaters; however, using beaters runs the risk of spreading mosaic virus.
Tubers, once harvested, require a dormancy period of four to eight weeks before they will sprout and grow.
To encourage seed potatoes to sprout, they can be treated with gibberellic acid, which is derived from seaweed. But by Thanksgiving, tubers that have been in storage will sprout readily with no treatment.
Wood Prairie Family Farm works seven days in Early March to keep up with shipping orders.
Jim’s Instruction for Planting Seed Potatoes
Gardeners can take tubers out of cold storage a week or two before planting and warm them up to encourage sprouting. Once they have sprouted, the tubers should be put under light so the sprouts stay compact.
A tuber the size of an egg should be cut in half before planting. A smaller tuber should be left whole. A tuber that is any bigger than an egg should be cut into multiple sections, each equal in size to half an egg. Every cut piece should weigh approximately 1.5 ounces.
In sandy soil, gardeners can cut seed potatoes and plant them immediately. But in clay soil, which holds water, Jim advises letting the cuts callous over for three or four days before planting.
Another trick Jim recommends is dipping the exposed cut in agricultural lime to desiccate it, making it less welcoming to pathogenic fungi. Plus, potatoes love the calcium in lime.
The seed pieces should be planted between 2 and 4 inches deep. Any deeper risks the tubers sitting in wet soil, though in the South Jim says gardeners should plant as deep as 6 inches and cover the area with straw mulch to keep them from drying out completely.
Hilling Up Potatoes
“Hill up” potato plants by adding soil around the stem once the top growth is 4 to 6 inches above the soil. This will prevent sunburn and the hills will drain water more readily. Straw, peat moss or leaves topping the hill will prevent sunburn and rotting.
Older, heirloom potato varieties will grow tubers up the stem, so hilling up is all the more important when growing those varieties. Most modern varieties set tubers deep in the hill
Potatoes perform their best when given plant food and a lot of water. They require calcium, potassium and phosphorus, but not too much nitrogen. Fishmeal is a good potato fertilizer, and Wood Prairie Family Farm sells a proprietary organic fertilizer formulation.
Controlling Common Potato Pest & Disease Issues
Colorado potato beetle – Handpick beetles at least twice a week, and the pest population will never develop pesticide resistance. For large-scale pest infestations, organic growers can use Entrust or another organic insecticide containing spinosad, but the beetle population will become resistant over time.
Potato leafhopper – Potato leafhoppers are fast, tiny, hard-to-see bugs that show up in warm weather. If control is necessary, there’s PyGanic 5.0, an organic, broad-spectrum contact insecticide made from pyrethrin.
Potato late blight – This occurs in moist weather when fungal spores are present. Certified organic farmers may use copper-based fungal controls for late blight, though must be sprayed on foliage before infection.
Potato scab – Scab is a bacterial disease typically introduced to soil on seed potatoes. Minimize scab by having adequate phosphorus and mycorrhizal fungi. Scab likes alternating wet and dry conditions and raw horse manure, so let horse manure rot down into compost before using it as a fertilizer. Scabby potatoes are still edible.
How to Harvest & Store Potatoes
Potato tubers are edible from the time they are the size of a pea. When potato plants blossom, the tubers will be ping-pong ball size. Then about six weeks after flowering, the foliage dies back and the tubers will reach their full size.
Tubers can stay in the ground for four to six weeks after the top growth has died. During this time, the skin dries out and toughens up, making the tubers better suited for storage and less prone to bruising. But if there are heavy rains in the forecast or the ground is expected to freeze, harvest them sooner.
If just looking for a couple of potatoes to have with dinner, reach gently into a hill and feel around for large tubers, pull them out, and leave the rest of the plant to continue growing. To take a whole plant out of the ground, loosen up the soil with a garden fork and lift the plant by the dead foliage. Dig around gently for any tubers left behind.
To store tubers to enjoy through fall and winter, hold off on harvesting until four to six weeks after the foliage has died naturally so the tubers will have had time to toughen up.
Potatoes can last in storage for up to 10 months in cool, dark conditions: 38° and high humidity.
If you haven’t already listened to my conversation with Jim Gerritsen on how to grow epic potatoes, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
What are your tricks to grow epic potatoes? Let us know in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Master Seed Starting: Everything you need to know to start your own plants from seed — indoors and out.
joegardener Online Gardening Academy Organic Vegetable Gardening: My new premium online course membership opens in 2023. Sign up for the waitlist here.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Growing Epic Tomatoes: Learn how to grow epic tomatoes with Joe Lamp’l and Craig LeHoullier.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, AeroGarden, Milorganite, Soil3, Greenhouse Megastore, PittMoss, Territorial Seed Company, Earth’s Ally, National Wildlife Federation, Proven Winners ColorChoice and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.