How to Grow Potatoes in Pots

Pick the container: size and drainage

Extension sources split on size. University of Maryland Extension lists potatoes at about 30 gallons of potting mix, and NC State says containers or grow bags should hold at least 30 gallons and be at least 2 feet deep. UGA Extension in DeKalb County and UNH Extension both describe a 10 to 15 gallon container about 2 to 3 feet tall as ideal.

These recommendations fit together better than they first seem. UNH budgets about 5 gallons of mix per plant. A 15-gallon can grows about three plants, and a 30-gallon tub grows more. What matters is volume per plant, plus drainage.

Don’t go much taller than 3 feet. UNH explains that in a tall container the top dries out long before the bottom, which stays soggy, and the soggy layer is where tubers rot. UGA makes the same point, noting that Phytophthora infestans, the late blight pathogen, thrives in cool, wet conditions.

Almost anything opaque works if you can drill holes in the bottom: a plastic trash can, a storage bin, a half barrel or a fabric grow bag. It needs to be opaque because tubers that catch light turn green.

Fill with potting mix, not garden soil

Garden soil compacts in containers. It drains poorly, dries hard and can carry weeds and disease. UNH recommends a half-and-half blend of soilless potting mix and good compost. The DeKalb County class used potting mix mixed with compost.

Seed potatoes and variety

Use certified seed potatoes. Grocery-store potatoes are typically treated with sprout inhibitors (UGA, UNH). Cut large seed potatoes into pieces about 1 to 2 inches across with at least one eye, or two eyes as UGA recommends. Let the cut surfaces dry for a day or two before planting so they’re less likely to rot. Small seed potatoes can go in whole.

UNH suggests that mid- and late-season varieties suit containers better than early ones because they keep forming tubers for longer. Container potatoes tend to stay smaller than garden-grown ones, so expect plenty of small and medium potatoes rather than big russets.

Planting and layering

Container potatoes follow the same timing as the garden crop. Plant them about 2 to 3 weeks before your last frost, using the dates for your zone above. UNH asks for at least 6 to 8 hours of direct sun.

1. Put 4 to 8 inches of mix in the bottom. UGA used 4 to 6 inches and UNH 6 to 8.
2. Set seed pieces eye side up, about a foot apart.
3. Cover them with another 4 to 6 inches of mix and top it with a little straw.
4. As the stems grow, keep adding mix around them. UNH leaves about 6 inches of leafy growth showing each time.

Layering works because new tubers form on buried stem above the seed piece. More buried stem gives the plant more room to set tubers.

Water and feeding

Containers dry out much faster than garden beds, and uneven moisture causes knobby, cracked tubers. Water whenever the top 1 to 2 inches feel dry, and keep going until water runs out the bottom (UNH). Keep the mix moist but never soggy.

Potting mix holds few nutrients. UNH suggests a water-soluble fertilizer every couple of weeks once shoots appear, ideally one with more phosphorus than nitrogen, such as 5-10-10. UGA’s class used 10-10-10 and notes the plants may need feeding about halfway through the season and again a few weeks before harvest.

Harvesting a container

Harvest timing is the same as in the ground. Take new potatoes once the plants flower by reaching gently into the mix. For a storage crop, wait until the tops yellow and die back. To empty the container, spread a tarp, tip the container over, and sift through the mix by hand (UNH). Handle the potatoes gently, keep them out of the light while they dry, and don’t wash them until you’re ready to cook.