How and Whether to Hill Potatoes

Why hilling is worth doing

The main reason is greening. The University of Minnesota Extension states that hilling keeps any shallow tubers from exposure to light and turning green, and warns that sunlight can turn potatoes green and cause the formation of potentially toxic and bitter-tasting chemicals in the skin and flesh.

There is a yield angle too. UMN notes that tubers form on thin stems, also called stolons, which emerge from the main stems, and that the longer the underground portion of the plant, the more stolons the plant may grow, so mounding soil up the buried stem gives the plant more room to set tubers.

The University of Georgia Extension frames it simply: forming a hill around the plant provides room for developing tubers to expand and prevents greening from the sun. A mounded row also sheds water and can smother weeds coming up between plants.

When and how to hill

Timing is forgiving but not open-ended. The University of Minnesota Extension advises to start hilling the plants when stems are about a foot tall, and once or twice more during the growing season, ending with six to eight inches of soil hilled in total along the plants.

The University of Georgia Extension puts the first pass a little earlier, recommending that when the sprouts are out of the ground about 6 inches high, you begin hilling soil around them, pulling soil from between the rows with a hoe and being careful not to dig too deeply and injure roots.

1. 1Wait for 6-12 inches of growth — Let the shoots reach roughly 6 inches to a foot tall before the first hilling so there is enough stem to mound against.
2. 2Pull soil up from the row middles — Draw loose soil from between the rows up around the stems with a hoe, burying the lower portion of the stems but leaving the top leaves exposed; work shallow so you do not slice roots or tubers.
3. 3Repeat once or twice — Hill again as the plants grow, adding soil a second time about two weeks later per UMN, until you have mounded a total of six to eight inches. Aim to finish most hilling before or around flowering.

The mulch alternative

If digging soil up every couple of weeks is not appealing, a heavy organic mulch does the same light-blocking work. The University of Georgia Extension suggests you fluff up straw or mulch over the potatoes to help prevent sunlight from penetrating down to the crop, and states plainly that potatoes that develop in sunlight will be green and inedible.

UGA adds a bonus: mulching the soil can help conserve water, reduce weeds, and keep the soil temperature lower, which can lengthen the growing period. So the choice between soil hilling and deep mulch is largely about which is easier for you, since both keep the tubers dark.

✔ The greening you are preventing is only skin-deep chemistry, not a plant disease. Even a stray tuber that pokes out and greens up just needs to be pulled and discarded (or the green part cut away), and the rest of the hill is fine. When in doubt, cover exposed shoulders with more soil or mulch.

Sources

Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.

• University of Minnesota Extension — Growing potatoes in home gardens — Verifies to start hilling when stems are about a foot tall and once or twice more during the season, ending with six to eight inches of soil hilled along the plants; that hilling keeps shallow tubers from exposure to light and turning green; that sunlight can turn potatoes green and cause formation of potentially toxic and bitter-tasting chemicals in the skin and flesh; and that tubers form on stolons emerging from the main stems, so a longer buried stem can grow more stolons.
• University of Georgia Extension — Home Garden Potatoes (Circular 1011) — Verifies that when sprouts are about 6 inches high you begin hilling soil around them, pulling soil from between rows with a hoe without digging too deeply and injuring roots; that forming a hill provides room for developing tubers to expand and prevents greening from the sun; that fluffing straw or mulch over the potatoes helps prevent sunlight from penetrating to the crop; that potatoes developing in sunlight will be green and inedible; and that mulching conserves water, reduces weeds, and lowers soil temperature.

Keep going