Starting potatoes indoors is an effective way to gain a significant advantage in the growing season, particularly beneficial for gardeners in regions experiencing short spring periods or unpredictable late frosts. This process does not involve growing the entire plant indoors, but rather initiating the tuber’s growth cycle to ensure it is robustly prepared for outdoor planting. The primary indoor activity is known as “chitting” or pre-sprouting, which awakens the potato from dormancy before it is placed into a growing medium. By taking these initial steps inside, gardeners can effectively shave off up to two weeks of outdoor growing time, leading to an earlier and often more abundant harvest.
Preparing Seed Potatoes Indoors
The first step in this process is selecting certified, disease-free seed potatoes, which are specially grown for planting rather than consumption. To begin the pre-sprouting, or chitting, phase, the tubers should be placed in a single layer with the end containing the most “eyes”—known as the rose end—facing upward. Using shallow trays, egg cartons, or open-topped boxes helps keep the potatoes separate and prevents them from rolling around.
They should be kept in a cool, bright location that is shielded from direct sunlight and frost. An ideal temperature range for this stage is approximately 50–60°F (10–16°C).
The light exposure encourages the development of short, sturdy, dark green or purplish sprouts, which are preferable to the long, white, and brittle sprouts that develop in darkness. This chitting process typically takes between four to six weeks, after which the sprouts should measure about half an inch to an inch (1–2.5 cm) in length. If the seed potatoes are particularly large, they can be cut into pieces, each containing at least two eyes, but the cut surfaces should be allowed to dry and callus for 24 to 48 hours before chitting to prevent disease.
The Indoor Planting Process
Once the seed potatoes have developed robust sprouts, they are ready to be moved into a growing medium indoors to initiate root and foliage growth. This transition usually occurs about two to four weeks before the last expected frost date in your region. Select deep containers, such as pots or fabric grow bags (often 10 to 15 gallons), that offer sufficient depth for tuber development.
The container should be filled with a loose, well-draining potting mix blended with compost, which provides necessary nutrients and aeration. Avoid using dense garden soil, as it compacts easily and retains too much water, potentially hindering drainage. The chitted potatoes are planted shallowly, with the eyes facing up, and covered with about four to six inches of the prepared soil mix.
A strong light source is needed for this stage, as the plants require bright light for 8 to 10 hours daily to support leaf and stem growth. If natural sunlight is insufficient, a full-spectrum LED grow light is an effective substitute to provide the necessary intensity. Unlike the cooler chitting phase, the temperature for active growth should be warmer, ideally remaining below 75°F (24°C) to ensure proper tuber formation.
Watering should be managed carefully, keeping the soil consistently moist but never waterlogged to prevent rot. As the stems emerge and grow taller, soil or compost can be gradually added around the base of the plant, a process known as hilling, which encourages the formation of new tubers along the buried stem.
Transitioning and Final Planting Outdoors
Before the indoor-started potato plants can be moved permanently to the garden or a final outdoor container, they must undergo a careful process called “hardening off.” This procedure gradually acclimatizes the tender indoor foliage to the harsher, fluctuating conditions of the outdoors, including direct sun, wind, and cooler temperatures. Failure to harden off the plants can result in significant leaf burn, wilting, and overall shock.
The hardening off process should take place over a period of seven to ten days. Begin by placing the containers in a sheltered, shaded outdoor location for just a few hours on the first day, ensuring they are protected from strong wind and intense midday sun. Each subsequent day, the exposure time is incrementally increased, and the plants are moved into brighter, slightly less sheltered spots.
The final planting outdoors should only occur after the danger of the last hard frost has passed and when the soil temperature has warmed sufficiently, ideally reaching at least 45–50°F (7–10°C). For in-ground planting, the plants are set into trenches or holes, which are then gradually filled in as the stems grow, continuing the hilling practice started indoors.