Why, When and How to Hill Potatoes



Maybe you hoped you could just drop your seed potato pieces in the ground, cover them over and wait for potatoes. More likely, you’d heard that you would need to hill your plants. Here I’ll explain why we do this, when to do it, how to hill, plus a couple of alternatives to hilling.

Initial Potato Development Stages and The Main Reason to Hill: More Potatoes!

The first things the seed potato does after planting is to produce roots, stems and leaves. This vegetative growth stage lasts 30 to 70 days. Bigger plants can yield more potatoes, so the goal for this stage is to produce large sturdy plants. Vegetative (leafy) growth of potatoes is favored by warm, 80°F (27°C) moist weather, but tuber growth is favored by cooler soil conditions of 60°F to 70°F (15.5°C to 21°C). This combination can be achieved in spring, when the soil is cooler than the air temperatures most of the time, or if you are planting in early summer, add organic mulches to keep the soil cool.

Tuber (potato!) formation and branching of the stems comes after the vegetative growth stage. All the potatoes that will grow on that plant are formed in this important two-week period. Flowering can happen too, but it’s not essential, so don’t worry if you get few or no flowers. The number of tubers produced per plant depends on the hours of daylight, temperature and available water in that short period of tuber initiation. Hilling adds soil to the stems, encouraging stem growth and providing more sites for potatoes to form.

Watering also stimulates the production of more tubers. When tuber formation begins supply 5 gallons per cubic yard (22.8 liters per square meter) of water. Water at this critical time, even if you can’t water at any other time. Short day length is optimal, with a night temperature of 54°F (12°C). High nitrogen also inhibits initiation. During this stage, leaf growth continues (the plant gets bigger).

When and How to Hill Potatoes

Start hilling (pulling soil up over the potato plants in a ridge) when the plants are 6” (15 cm) tall. Hill again two or three weeks later and two more weeks after that, if the plant canopy has not already closed over, making access impossible.

On a small scale, use a rake or standard hoe to pull soil up from the side of the row opposite to where you are standing. If you are sharing the job, one person can work each side of the row at the same time. If you are alone, turn round when you get to the end of the row and work back up the same row. Don’t be tempted to twist your arms around and move the soil up the side nearest you. You will damage your body by this distortion of your spine and shoulders!

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