Potatoes are a rewarding crop for the home garden. Success depends heavily on proper planting technique, especially depth management. Getting the initial depth correct and managing the soil depth as the plant grows is fundamental to maximizing yield and ensuring the tubers are safe to eat. This requires balancing protection for the seed piece with providing space for new potatoes to form.
Preparing the Planting Site and Seed Potatoes
A suitable growing environment must be established before planting. Potatoes thrive best in loose, well-draining soil, such as a sandy loam, allowing developing tubers to expand easily. The ideal soil pH is slightly acidic, generally between 5.5 and 6.5, which helps prevent the common potato disease known as scab. Incorporating organic matter like compost or well-rotted manure improves fertility and drainage, preventing waterlogging and rot.
Use certified, disease-free seed potatoes, as grocery store potatoes may introduce diseases or result in poor growth due to chemical inhibitors. Larger seed potatoes should be cut into blocky pieces, weighing 1.5 to 2 ounces and containing at least one or two eyes (buds). After cutting, allow the pieces to sit in a dry, airy place for a couple of days to form a protective callus. This leathery layer helps prevent the seed piece from rotting once planted. Seed pieces should be spaced roughly 10 to 12 inches apart within the planting bed.
Determining the Initial Planting Depth
Initial planting depth is measured from the top of the seed piece to the soil surface after covering it. For most home gardens, the standard recommendation is to plant seed pieces in a trench 3 to 5 inches deep. This depth shields the seed potato from temperature fluctuations and light, while allowing the plant room to establish roots. Planting too shallowly risks drying out, while planting too deep can delay emergence or increase the risk of rotting in heavy or cold soil.
A slightly deeper initial planting of 6 inches may be used for later-season varieties or if the gardener intends to plant in a trench and add only a small amount of cover soil initially. When planting in containers, the initial depth is similar, but the container should be at least 16 inches deep overall to accommodate the continuous addition of soil. The initial layer of soil covering the seed piece should be loose and well-worked to encourage shoot growth and prevent early resistance.
Managing Depth Through Hilling and Earthing Up
The initial planting depth is temporary because new potatoes, which are stem tubers, form along underground stems called stolons that grow above the original seed piece. To ensure high yield and prevent toxicity, gardeners must continuously manage the soil depth over these developing tubers through hilling or earthing up. Hilling involves mounding additional soil, compost, or straw around the base of the growing plant stem. This action increases the depth of the growing medium, providing more space for new stolons and tubers to form.
The primary reason for hilling is to shield forming tubers from sunlight exposure. When exposed to light, tubers produce chlorophyll, turning the skin green, and generate solanine. Solanine is a toxin that gives the potato a bitter taste and can be harmful if consumed in large quantities. Hilling should begin once plant shoots reach 6 to 8 inches in height. Soil should be mounded around the stems, leaving only the top few inches of foliage exposed. This process is repeated every few weeks as the plant grows, building a substantial hill of 6 to 8 inches by the end of the season.