The term "seed potato" can be a little misleading. Although potatoes do set seed, they do not grow true to seed. To get the variety of potato you want, you need to grow them vegetatively, meaning you re-plant a part of the actual potato. These pieces of potato are referred to as seed potatoes.
Selecting Seed Potatoes
Because potatoes are propagated vegetatively, any diseases from the prior year will be carried over. That's why it is so important to use disease-free seed potatoes. That means certified seed potatoes, rather than supermarket potatoes. Certified seed potatoes are certified by a government authority to be disease-free.
However, even certified potatoes can contract disease once planted, especially diseases that are not apparent in the seed stage like ring rot or fusarium wilt. Still, at least you have a bit of an edge, with some disease tolerance.
Any potatoes that have a soft spot, cracks or bruises or signs of rotting should be discarded. Start with the healthiest, strongest seed potatoes to avoid problems and guarantee a good harvest.
What Exactly Do You Plant?
You do not need to plant a whole, intact potato. Seed potatoes can be cut into pieces, as long as the pieces have at least one eye each. An "eye" is a bud that grows into a new plant. If you've ever kept your potatoes in the cabinet too long, you've probably seen them sprout.
You can plant whole potatoes or pieces with multiple eyes, but in general:
- More eyes per piece = more, but smaller potatoes
- One or two eyes per piece = less, but larger potatoes
It all depends on what you want.
Preparing Seed Potatoes
If you decide you want to cut your seed potatoes into pieces, cut them about two days before you plan to plant. This allows the pieces to callus or seal and prevents rotting and soil-borne diseases while the pieces sprout and take root.
To further protect your seed potatoes, you can dust them with powdered sulfur right after cutting them. Place the potatoes in a bag, add the sulfur and shake. Then lay the pieces out and let them dry for three to four days.
To Chit or Not to Chit Potatoes
Chitting is the term for pre-sprouting your seed potatoes, before planting. It may also be referred to as "greening". Many gardeners feel this give them a head start, but you do not have to chit your potatoes to get a good crop. The two circumstances, when chitting is advised are:
- If your seed potatoes are already sprouting.
- If you have an early-maturing variety and want an early harvest.
How to Chit
Although potatoes will sprout in the dark, you will get long, pale shoots that easily break. Instead, place them in a cool (winter room temperature) spot with bright light. This way, the sprouts will grow stocky, sturdy and dark green.
A traditional method for chitting is to place your seed potatoes upright in an egg carton, with the bud end facing up, but you can just lay them out on a tray or screen, as long as they are not piled one on top of another.
It will take about two to four weeks for the chits to develop, so don't start until about one month before your outdoor planting date. (Potatoes will store for several months without sprouting if kept dark and at about 40 F / 4 C) .
Planting Your Seed Potatoes
You can plant your potatoes as soon as the sprouts on the potatoes are 1/2 inch to 1 inch long. If you have to postpone planting because of weather or some other reason, move them to a cooler spot, to slow down their growth. Don't want too long, or your seed potatoes will dehydrate and begin to shrivel.
Handle the seed potatoes carefully, so the sprouts do not break off or become damaged. You can plant the whole potato or cut into pieces with at least one eye each, but do this after chitting, not before. Plant with the sprouts facing up and cover lightly with soil.
How Much Should You Plan on Planting?
On average, one pound of seed potatoes should yield about 10 pounds of potatoes. One pound is about 5 to 8 tubers, which should be enough to plant about a 10-foot row.