Some plants are routinely started indoors, either because they benefit from a controlled climate during their early growth or because otherwise their growing season would be too long for most gardeners. Potatoes (Solanum tuberosum) don't usually fall into that category. They're typically planted fairly early in the spring and have time to mature even in short-season climates. That being said, they can be transplanted successfully if you have reason to try it.
Why Transplant Potato Plants?
Growing potato seedlings for transplant is relatively rare in the home garden, though it's sometimes done by commercial growers. There are several reasons you might wish to try it, including, but not limited to:
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- They offer a bit of insurance, in case flooding, disease or poor germination should give you mediocre results from your direct-planted seed potatoes.
- It's a way to grow potatoes in an exceptionally short-season gardening scenario.
- It's a solution for when you won't have access to your garden plot until a few weeks into the growing season.
- You want to try a longer-season variety that might not ordinarily have time to mature in your climate.
- You plan to grow potatoes in containers, and wish to have healthy transplants as your starting point.
Whatever your reason, potatoes require a bit more care than commonly transplanted vegetables like tomatoes and fresh herbs. You'll have to treat them differently at planting time and transplant them with extra caution.
Things You'll Need
Certified disease-free seed potatoes
Seed-starting drip/drainage tray
How to Grow Potato Seedlings
Because potatoes are grown from tubers, rather than seeds, you'll need to start by preparing the seed potatoes for planting. You'll also need to use larger starter pots — at least 3 or 4 inches — rather than the smaller cell-type starter trays used for smaller seeds.
Step 1: Prep the Seed Potatoes
Cut the seed potatoes into pieces approximately 1 to 2 inches in diameter and 1 1/2 to 2 ounces in weight, each with at least one or two small buds, or "eyes." A large seed potato might yield four or more pieces. Smaller ones can be halved or left intact.
Step 2: Cure the Seed
Leave the cut-up seed potatoes spread out in a single layer in a warm, dark, well-ventilated space for at least one or two days. The cut surfaces will cure, or scab over, reducing the risk that they'll simply rot once you place them in the soil.
Step 3: Prepare Your Potting Medium
Make up a potting mixture by combining equal parts of a soilless potting mix and high-quality compost — the same mixture you'd use if you were growing potatoes to maturity in a container.
Step 4: Prepare the Pots
Prepare a 3- or 4-inch pot — either a conventional pot or the thin disposable type used for seedlings, for each piece of seed potato. If the pot has been previously used, wash it in hot, soapy water with a splash of bleach and then dry it thoroughly. Fill them halfway with your potting medium.
Step 5: Plant the Potatoes
Place a cured piece of seed potato in each pot, with the eyes facing upward. Fill the pot the rest of the way with your potting medium, using your fingertips to compress it gently. Place the pots in a tray filled with water and let them absorb as much as they'll hold. Then, move them to a drip tray.
Step 6: Grow Out Your Seedlings
Move the newly planted seed potatoes to a cool, sunny, well-ventilated location, and water them lightly but frequently whenever the soil feels dry. You'll typically see green sprouts within 10 to 14 days. They can be planted out, or moved to a larger pot or container once they've reached 4 to 6 inches in height.
How to Transplant Potato Seedlings
Step 1: Harden Off the Seedlings
Prepare the seedlings for transplant by exposing them to the outdoors, or "hardening them off," for at least two days and up to a week. Take them out for a bit longer each day until they're spending all day out in the wind and sunshine. This acclimates them to outdoor conditions and minimizes transplant shock.
Step 2: Prepare the Potato Bed
Dig over the bed, once it's dry enough to be worked, and then rake it smooth. Potatoes need to be spaced about a foot apart, so it's easy to calculate how much space you'll need. Dig a trench or individual holes for your seedlings to the depth of the soil in their starter pots.
Step 3: Unpot the Seedling
Choose a starter pot and place your hand carefully around the seedling, holding it protectively in place, then tip the pot upside down and coax the soil and root ball out into your hand. Take great care to remove soil, roots and plant all in one piece; if you break off the seedling's stem you may or may not be lucky enough for another to grow from the seed piece.
Step 4: Plant the Seedling
Tip the seedling carefully upright, and place it gently in the prepared hole or trench. Pack soil in around it, until it's completely surrounded. The soil should come at least to the level of the starter mix surrounding your seedling, or even slightly higher. Repeat for any remaining seedlings.
Step 5: Water in Your Seedlings
Water the seedlings thoroughly, so the soil is wet but not sodden (potatoes will rot in soggy soil). Monitor the soil's moisture level carefully, and water the transplants as needed. The soil should be consistently moist, but not wet.
Step 6: Weed As Needed
Weed the potato bed frequently for the first four to six weeks, until your transplants are large and vigorous enough to out-compete any weeds. It's better to pull weeds by hand than to use a cultivator or hoe, because potatoes grow just under the soil, making it likely that you'll disturb them and reduce your harvest if you cultivate too deeply.