Planting Seed Potatoes on a Small Farm for Bigger Yields

You put a whole bed of potatoes in, hilled them twice, and dug up a crop of marble-sized tubers or a few big rotten ones. Most of the time the problem started on planting day, not at harvest.

Planting seed potatoes well comes down to four things: clean seed, the right soil temperature, correct cut size, and enough room between plants. Get those right and a 100 foot row can return 150 to 200 pounds. Get them wrong and you will spend all summer weeding a row that never pays you back. Here is how I plan and plant potatoes on a small market garden, from ordering seed in winter to the first hilling.

Ordering seed and planning the row

Buy certified seed potatoes from a seed company or farm supply store, not grocery store spuds. Grocery potatoes are often treated with sprout inhibitors and are not inspected for viruses or blight. Certified seed costs more, usually $1.50 to $3 a pound in small lots, but a single disease introduction can sit in your soil for years.

Plan on roughly 10 to 12 pounds of seed per 100 feet of row. For a quarter-acre block in 3 foot rows, that works out to around 400 pounds. Order in December or January, because popular varieties sell out by February.

Mix maturity groups so your harvest is spread out. A simple split for a small farm:

• Early (70 to 90 days): Yukon Gold, Red Norland, Dark Red Norland. Good for June and July markets.
• Mid-season (90 to 110 days): Kennebec, Red Pontiac.
• Late (110 to 135 days): Russet Burbank, Butte, German Butterball. Best for storage.

Rotate. Do not plant potatoes where tomatoes, peppers, eggplant or potatoes grew in the last three years. If you need a simple way to stagger your other crops around this block, see succession planting without a spreadsheet.

When to start planting seed potatoes

Go by soil temperature, not the calendar. Potatoes want soil at 45 to 50 degrees F at 4 inches deep. Colder than that, seed pieces sit and rot. A $12 soil thermometer pushed in at 8 a.m. for three mornings in a row gives you a reliable reading.

In most of the northern US that lands in mid-April to early May. A common rule ties planting to two to four weeks before your last frost date. Light frost will nip emerged leaves, but the plants regrow from below ground as long as the tubers are not frozen.

Drainage matters as much as warmth. If you squeeze a handful of soil and it stays in a sticky ball, wait. Working wet ground compacts it, and compacted soil grows misshapen, small potatoes.

Cutting and chitting seed pieces

Small seed potatoes, about the size of a hen's egg (1.5 to 2 ounces), can go in whole. Anything larger should be cut. Each piece should weigh 1.5 to 2 ounces and carry at least two eyes. Pieces smaller than an ounce produce weak plants because the seed piece feeds the sprout for the first few weeks.

Cut seed two to five days before planting and keep the pieces at 50 to 60 degrees F with good air flow. The cut surface will form a dry, corky layer, called suberizing, that resists rot in cool soil. Spread them one layer deep on a tarp in a shed, not in a sealed bucket.

Chitting, or pre-sprouting, gives early varieties a head start of a week or two. Set whole seed in shallow trays in a bright spot at 55 to 65 degrees F for two to four weeks until sprouts are about half an inch long, short, green and stubby. Long white sprouts from a dark cellar snap off when you plant them, so do not count those as chitted.

Spacing, depth and fertility

Open a furrow 4 to 6 inches deep. Set seed pieces cut side down, 10 to 12 inches apart, in rows 30 to 36 inches apart. Tighter spacing, around 8 inches, gives more small potatoes, which is useful if you sell new potatoes or fingerlings by the pint. Wider spacing, around 14 inches, grows larger bakers.

Cover with 2 to 3 inches of soil at first. You will add the rest as you hill.

Potatoes like slightly acid soil, pH 5.2 to 6.5. Do not lime the potato block right before planting, because higher pH favors common scab, the rough corky patches that make tubers hard to sell. Band a balanced fertilizer or well-finished compost 2 inches to the side of the seed rather than right on top of it. Fresh manure is a bad idea here, since it also encourages scab.

Hilling, and why I hill less than most guides say

The standard advice is to hill potatoes three or four times, piling soil up until the ridge is a foot tall. On a small farm with limited hours, I think that is overdone.

Hilling has two real jobs: keep developing tubers covered so they do not turn green from sunlight, and knock back weeds while the canopy fills in. Two hillings do both. The first goes on when plants are 6 to 8 inches tall, pulling 3 to 4 inches of soil around the stems. The second follows two to three weeks later, just before the rows close.

Extra hillings after that disturb shallow roots, dry out the ridge, and cost labor you could spend elsewhere. Most varieties set tubers in a fairly narrow zone above the seed piece, so a taller hill does not mean more potatoes. If you want to stop greening without more hilling, a 3 inch layer of straw mulch after the second pass works well and holds moisture through July.

Watering and the first weeks after emergence

Potatoes need about 1 to 2 inches of water a week, and the most important stretch is from flowering through tuber bulking. Uneven water during that period causes hollow heart, growth cracks and knobby tubers. Drip tape laid on the ridge after the final hilling is the easiest fix.

Scout for beetles as soon as leaves appear. Our guide to Colorado potato beetle control on a small farm covers hand-picking and row cover timing, which matter most in the first three weeks after emergence.

Frequently asked questions

How deep should you plant seed potatoes?

Plant seed pieces 4 to 6 inches deep in a furrow and cover them with 2 to 3 inches of soil at first. As the plants grow you add soil by hilling. In heavy clay, stay toward the shallow end so the pieces do not sit in cold, wet soil.

Should seed potatoes be cut before planting?

Cut seed potatoes larger than a hen's egg into 1.5 to 2 ounce pieces with at least two eyes each. Let the cut pieces cure for two to five days in a cool, airy spot before planting. Small whole seed needs no cutting and is less prone to rot.

How many potatoes do you get from one seed potato?

A healthy plant usually yields 3 to 5 pounds, or about 8 to 15 tubers, depending on variety and spacing. That works out to a return of roughly 10 to 15 times the seed weight. Drought, poor drainage and late planting all cut that number sharply.