Potato cultivation requires a specific technique called “hilling” to ensure a successful harvest. Hilling is the practice of mounding soil or other material around the base of the growing potato plant’s stem. This method is fundamental because potatoes, unlike many other root vegetables, do not form from the main root system. Hilling creates an extended, dark environment that encourages the plant to produce tubers where they are protected and can grow larger.
Why Hilling Potatoes is Essential
Hilling serves two main functions that directly affect the yield and edibility of the crop. First, it prevents developing tubers from being exposed to sunlight. Light exposure causes tubers to turn green due to chlorophyll production, which also triggers the creation of solanine. Solanine is a naturally occurring toxin that makes green potatoes unsuitable for consumption.
Second, hilling increases the overall number of potatoes produced by each plant. Potato tubers form on specialized underground stems called stolons. By continually mounding material around the main stem, you lengthen the portion of the plant buried beneath the surface. This extended underground stem provides more available surface area for new stolons to form, maximizing the potential space for tubers to develop and grow.
Recognizing the Initial Timing
The time to perform the first hilling is based on the physical growth of the plant, not a calendar date. Begin the process when the potato foliage first reaches a height of approximately 6 to 8 inches above the ground. Waiting for this visual cue ensures the young plant is established enough to handle having its lower leaves covered.
During this initial hilling, the goal is to cover about two-thirds of the visible plant growth with your chosen material. Mounding a layer of soil or mulch 4 to 5 inches high around the base leaves only the top leaves exposed. This action protects any tubers already forming near the surface and prepares the stem for the next stage of growth.
Techniques and Materials for Hilling
The method for hilling depends on whether the potatoes are planted in traditional rows, raised beds, or containers. In garden rows, use a hoe or shovel to pull existing soil from between the rows up and around the base of the stems. For raised beds or containers, you must add new material, such as loose soil and compost, up to the required height.
Avoid compacting the material around the stem, as potatoes thrive in loose, well-draining conditions. The best materials for hilling are loose soil, well-aged compost, or organic mulches like straw or hay. Straw is often favored for later hillings because it is lighter and makes the final harvest much easier.
When applying the material, gently create a mound around the stem, ensuring it has a gentle slope rather than steep sides. The focus is to completely bury the stem without damaging the tender foliage or the plant’s main growing points. After hilling with soil, a light watering helps the new material settle around the plant’s base.
Ongoing Hilling and Season Completion
After the first hilling, the process becomes a recurring maintenance task throughout the growing season. As the foliage reaches another 6 to 8 inches in height, it signals the need for the next application of material. This typically means hilling every two to three weeks, depending on the speed of growth in your specific climate.
Continue to repeat the hilling process until the plant begins to flower. Flowering indicates that the plant is shifting its energy from vegetative growth to tuber development underground. Once the plants have flowered, or once the hills have reached a height of 12 to 18 inches, no further hilling is necessary. At this stage, the plant has enough buried stem to produce a good crop, and the thick canopy of leaves will help shade the soil surface.