Did you know? There are over 100 potato varieties grown in the United States alone, and more than 1,000 different cultivars across the globe. And among that amazing diversity, there are plenty of great candidates for backyard gardeners in the Pacific Northwest looking to grow their very own potatoes for baking, roasting, or turning into French fries! All it takes is a sunny spot, a bit of patience, and high quality, organic seed potatoes like the ones we sell at Cornell Farm.
In spite of the name, seed potatoes aren't seeds or even grown from seed; rather, they are full-grown potatoes that you use to "seed" your beds at the beginning of the season. You will find several varieties here at the Farm each spring — sometimes as early as February — that can be planted out in your garden between March and May. Unlike potatoes for sale at your local grocery store that bear vague names like "russet," "yellow" or "red," purchasing certified seed potatoes allows you to know the exact cultivars you are buying, and the particulars of their color, taste, use, and storage value. Plus, you can rest easy knowing that they have been tested for common viruses that can hurt your yields and that they haven't been treated with any unwanted chemicals to keep them from sprouting in the produce aisle, and consequently, your garden!
Preparing Your Soil
Root vegetables like potatoes, beets, onions, garlic, carrots, turnips and radishes all perform best when planted in highly friable soils — soils that break apart easily in your hands without fully disintegrating like sand. Characteristically, these soils are high in organic content and, as a result, tend to be moisture-retentive yet well-draining. While many plants prefer to grow under these conditions, it is especially important to provide root vegetables with lightweight, fluffy soil so that their underground structures can reach their full potential in terms of size. Conversely, heavy clay soils can act like a "straight jacket" for developing tubers, resulting in smaller, often misshapen, potatoes.
If, like the majority of Portland gardeners, you weren't fortunate enough to inherit these perfect gardening conditions, never fear! There are many work-arounds at our disposal that allow us to successfully grow potatoes in our gardens. The first is to amend our native clay soil with compost to a depth of 8 inches, using a shovel or spade to chop the clay into smaller bits and create an even mixture. It's also a good idea to add dehydrated chicken manure to the mix to provide your potato plants with humus-rich conditions they crave. (Don't worry: Properly aged manure doesn't smell!)
Alternately, you can take the easier route and simply fill a raised bed or large container with a planting medium that is already light and airy, such as E.B. Stone Raised Bed Mix. This mix offers nutritious and well draining soil perfect for planting potatoes — not to mention a wide variety of other crops — and since it is specifically formulated for raised beds, you shouldn't need to add any additional fertilizers, amendments, or compost, allowing you to get straight to planting!
Planting & Tending to Your Potatoes
- When the sprouts are about 1/4 inch long, cut each seed potato into 1-2 ounce pieces, making sure there is at least one sprouted eye on each piece. (Any potato weighing less than 1.5 ounces should simply be planted whole.) Then, let these sliced sections cure in a dry, airy place that is out of the sun for 2 to 3 days; the resulting leathery film will help to protect your seed potatoes from drying out or getting too wet.
- Plant each piece so that the upward-facing sprout is about 1 inch beneath the soil surface. This will help your potato plant to emerge quickly and begin photosynthesizing right away.
- When the plants have reached 3 inches tall, mound the soil around each plant, leaving just the top few leaves above the soil. Continue doing this each week until you have a "hill" that is 5-8 inches tall. Using this method, the tubers will develop in the soft soil and be protected from the rays of the sun. During this time, you will want to keep the soil moist but not soaking.
- Once the plants are 12 to 14 inches tall, you can start to water your potatoes deeply, but you should plan to let the soil surface dry before watering again. (As a rule of thumb, the lighter soils that root vegetables grow so well in tend to dry out more quickly than heavy clay soils.)
- Twice during the growing season, you should fertilize your potatoes with a balanced all-purpose organic fertilizer to help them put on a nice crop.
Harvesting & Storing Your Crop
One of the nice things about growing potatoes is that, by harvesting incrementally, you don't have to wait until the end of the season to enjoy eating potatoes fresh from your garden! After about 2 months in the ground, you can gently dig around the edges of your plant and remove a few of the potatoes to eat. If you are careful not to disturb many of the roots, your plant will continue to set more tubers that will mature throughout the summer. It's best to only dig what you need at this point, as potatoes dug before the end of the season tend to be smaller with thinner skin, and do not keep for as long.
When you are growing potatoes for storage, you will want to let them stay in the ground to grow the full season — generally, sometime in early October for Portland gardeners. If your plants don't naturally turn yellow and begin to die back on their own, two to three weeks before you want to harvest, you should cut the plants off at ground level and let the soil begin to dry. Doing this will help the skin of your potatoes to toughen and be more resistant to bruising when harvest time comes around. Dig carefully (we recommend using a spading fork) to ensure that you don't slice into the potatoes underground!
Depending on the variety of potato you are growing, your exact yield will vary, but as a general rule of thumb, you can expect to harvest 8 to 10 potatoes per plant. When you store potatoes between 36 and 40°F in a dark place, they can last several months!