Farm Horizons, April 2015

Hilling potatoes: why it’s important

By Christine Schlueter, McLeod County Master Gardener

The main reason to hill potatoes is to increase yield.

Potatoes form along the underground stem of the plant, and when you hill them, effectively lengthen the underground portion of the stem. You can either add additional soil to the bed and then mold it around the plants, or you can scoop up soil from the rows and press it against the stems. Later in the season, it’s easy to reach in and check the potatoes for size before you harvest them.

One of the most important tasks when growing potatoes is hilling up soil around the plants. Once you have the seed potatoes planted, the potato plants will grow pretty quickly.

After the plants reach about eight to twelve inches tall, soil or straw needs to be hilled around the plants for the potato tubers to grow in. These “hills” are where the potatoes will form, and it’s important to keep them covered and away from sunlight.

If the potato tubers come in contact with sunlight they can become green and not fit to eat. In fact, green potatoes can carry toxins and could become poisonous.

To prevent this, potatoes should be hilled at least a couple times during their growth cycle. The more you can hill the potato plants, the more potatoes they will produce.

When I grow potatoes in a raised bed, I hill the potatoes twice, possibly three times, during their growth using soil and straw. Here’s how to hill potatoes grown in a raised bed.

Hilling Potatoes The First Time

Once the potato plants reach a height of eight to twelve inches tall it is time to hill up soil around the potatoes. If potatoes are grown in the ground, in rows, you simply use a hoe or shovel to hill the surrounding soil up around the plants. if you have them in a raised bed you will have to add soil.

Use a combination of good top soil and a little compost, added with vermiculite. You can also use a quality, organic potting soil. The vermiculite has water absorbing properties which helps keep the soil from drying out quickly.

Hilling soil around the potato plants is pretty straight forward – simply add soil around the potato plants until just the top sets of leaves are sticking above the soil.

Continue adding the soil around each plant until the raised bed is filled and just the top leaves are sticking above the new soil.

Cover the potato plants with soil, except for the very top leaves. Water the raised bed well, making sure the new soil is soaked thoroughly. Continue to keep the potato plants well watered for the next couple weeks.

After a couple weeks the potatoes should be ready to hill again. The potato plants typically grow fairly quickly, so keep an eye on them.

After a couple weeks, the potato plants should grow another eight to twelve inches tall. At this time they are ready to be hilled again.

For the second hilling I use straw around the potato plants. Using straw makes it much easier to harvest the potatoes when the time comes.

The trick to hilling potatoes with straw is to lay the straw down very thick. The thicker the straw, the better. Remember, we don’t want the potato tubers (the baby potatoes) to come in contact with light until they are ready to harvest.

The easiest way of laying the straw around the potato plants is to just use small handfuls of straw at a time.

Take the small handfuls of straw and carefully work it in around each plant in thick clumps. Take your time during this part to ensure you cover as many of the nooks and crannies as possible. Just work your way around each potato plant.

If you are having trouble filling in all the bare spots with straw you can use top soil and sprinkle it on top of the straw to fill in the empty places. This is also good insurance for avoiding any green potatoes.

Once you have completed hilling the potatoes with straw make sure to water the raised bed thoroughly. You may need to add more straw to the raised bed after it settles some from watering.

After a couple more weeks the bed can be hilled with straw again if needed. Now you should be on your way to some great potatoes!

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