When you are ordering your seeds, don’t forget to order your seed potatoes. “Seed potatoes” are potatoes for planting, not a true seed. Think of them as “starter” tubers. Seed potatoes are planted outdoors about 4 weeks before the average last frost date. In the DC metro area, this is March and many gardeners use St. Patrick’s Day as the traditional day of planting but later in March is okay too.
Local garden centers will sell a few varieties but you get a better selection if you contact companies specializing in potatoes. There is tremendous diversity of the tuber itself. There are white, blue, red, purple or gold colored tubers in small or large sizes, round and gnarly or thin and slender. In terms of cooking, tubers can be mealy like a Russet (good for baking but disintegrates in a stew) versus waxy like a Yukon Gold (holds its shape). Tubers also vary in maturation days: there are early season (90 days), mid-season (100-110 days), and late season (120 days) varieties. If you plant different varieties, you can harvest potatoes from June to August. Interestingly, the foliage does not vary. The plant grows to a few feet tall, flowers, and dies, signaling the time to dig and harvest the tubers.
It is best to start with seed potatoes that are certified as disease-free, instead of planting a grocery store potato. The shoots arise from the “eyes” and additional tubers appear along these shoots as they grow. Seed potatoes should be the size of an egg with at least two eyes. If the seed potato is this size already then plant the whole thing, eyes up. If the tuber is large, you can cut it into sections, each with at least two eyes. I have read differing opinions about whether you should let the cut end callous (to prevent disease). Some people cut and plant while others cut, let them callous over, and then plant.
I plant my potatoes in large fabric containers. This is a great way to grow potatoes if you do not have a lot of land or if your garden soil is too compact. Use fabric containers that are at least 20-gallon large with at least a 15-inch height. Estimate 4 plants in this size and more in larger sizes. I space my seed potatoes about 6 inches apart.
I use bagged potting soil and sometimes I find one that has a slow-release fertilizer. If not, I add Osmocote, a well-known slow-release fertilizer. Another option is to add a granular fertilizer or apply a liquid fertilizer several times. Because potatoes are heavy feeders, I supplement with a liquid fertilizer later in the season.
You can also grow potatoes in the ground, in large plastic containers with drainage holes, or in special containers meant for these tubers. If you grow in the ground, the soil should be loamy, well-drained, high in organic matter, and slightly acidic with a pH between 4.8 and 6.5. Usually, potatoes are planted in trenches 4 to 6 inches deep, spaced 18 inches apart. After planting, the trench is backfilled until level with the soil surface. As the plants grow, they are covered by pushing soil up and over from each side of the row while letting some foliage show to be able to continue to photosynthesize.
With my fabric containers, I pour about 3-4 inches of the soil in each container, water, and then place the potatoes on top, eyes up. I then add 3 more inches of soil, water again, and insert a plant label. I roll down the side so they do not turn inward and prevent rain from reaching the plants.
Since planting is in March, we may still have very cold temperatures. Potatoes are hardier than they look, the foliage is hardy to about 28 degrees and the roots can withstand even colder temperatures. Still if the forecast calls for a hard freeze in the night the plants can be covered with a blanket.
Potato plants need 6-8 hours of sunlight and more water than you think — an inch of water a week. If it does not rain, water with a hose. However, the foliage is susceptible to fungal diseases so water by putting the hose nozzle into the bag, not spraying the foliage and not watering in the evening.
They are susceptible to Colorado potato beetles so check the underside of leaves for the yellow/orange eggs. If you see these, remove immediately. If you are growing a lot of potatoes and this becomes laborious, you may want to use a Spinosad-based insecticide. Other issues are flea beetles or fungal disease although I find I do not have these issues with my fabric containers.
The new tubers grow up (vertically) from the seed potato. As the shoots grow (now stems), and more tubers appear, these new tubers have to be covered with soil. Tubers exposed to light become green and bitter. (This also is a tip for storing store-bought potatoes, keep them out of light in a cool place but not in the fridge). When the stems have grown about 8 inches, I “hill up” the potatoes which means I add about 4 inches of soil to cover the new tubers. Every few weeks, I repeat the process again, unfolding the sides as I add more soil. This process of adding more soil is called “hilling.”
In early summer, after the flowers fade, I can harvest immature tubers by pulling egg-size tubers out (leaving smaller ones in). This immature stage is what we buy as “new potatoes” in the store. New potatoes have a very thin skin and do not keep — they have to be eaten soon. We boil them and mix with parsley, chives, and butter.
In mid-summer, the potatoes will have matured so all of them can be harvested and they should last longer. When the plant’s leaves yellow and die, stop watering, wait two weeks, and then dump the container to harvest the potatoes. I dump the soil on a tarp to either use the soil to start a new garden bed or to put back in the containers and plant bush beans. Potato plants stop making tubers when soil temperatures rise above 80 degrees so they are really a summer producer. To have potatoes to eat in the winter, you want mature tubers that have been cured. Cure by storing in a dark cool place (not the fridge) with the soil still on them. Scrub clean before you eat them, not before storage.
One term that comes up with potatoes is “chitting,” which is common in England but not in this country. Chitting is the process of “pre-sprouting” the tuber before planting to give the plant a head start, much like starting tomatoes under lights in the house before May. Chitting affords an early harvest but takes space (in your house) and time.
To chit the potatoes, place tubers eyes up in an egg carton. Put next to a window in a warm place (the usual heated house). The type of grow lights used for starting seeds are not necessary. After they have sprouted (like old potatoes do in the vegetable bin), plant them outside. If the tuber is large, cut in the size of an egg with at least two eyes.
- Wood Prairie Farm
- Irish Eyes
- Fedco Seeds
- Johnnys Seeds
- Territorial Seeds
- Seed Savers Exchange
- Southern Exposure Seed Exchange
- Maine Potato Lady