Many gardeners who grow potatoes are not sure when to dig them up. Because potatoes grow underground, we cannot see their size, feel how solid they are or smell them to know when they are ready to eat.

If we dig potatoes up too early, they may be too small. This could stress the plant and its root system.

So how do we know exactly when to harvest?

Jessica Damiano writes about gardening for the Associated Press. She said the best time to start digging up potatoes is when half the plant's leaves have turned yellow. This will happen between 60 and 120 days from planting, depending on the weather and the kind of potato that is planted. You can stop watering the plants around this time.

To help the potatoes mature, especially in wetter climates, you should cut the plants at soil level. This step is not necessary, however. If the plants are not cut, they will just die back on their own. After two weeks, the potatoes are ready to harvest.

If you are still not sure about when to harvest, dig up a small test potato. Carefully dig into the soil near a tester plant, and take a potato from the outer part of the roots. The skin of a mature potato will stick to the potato if you run your fingers over it. If the skin rubs off, fill the hole back up and check again in about a week.

When digging, try to avoid cutting through the potatoes. You can use a digging instrument instead of a shovel to help. Allow 15 to 30 centimeters around the outer part of the plant before putting in the tool.

Then, carefully move the instrument back and forth to unearth the potatoes by lifting the roots. Do this in a circle around the individual plants. Make sure to go back through the soil and check for any remaining potatoes.

You can eat the potatoes right away or preserve them for later.

To preserve the potatoes, lay them out on a piece of thick paper, like newspaper. Then, place them in a cool, dark place that stays between 10 and 15 degrees Celsius. Keep them there for two weeks. This will help thicken their skin and close off any small cuts.

After preserving, store the potatoes in a much cooler area like an underground room that has good air flow and that is darker. The temperature should be about three to four degrees Celsius. If preserved and stored in this way, they should last six to eight months.

Avoid putting the potatoes in the refrigerator. This will intensify the sugars and change their flavor. Injured potatoes will not store as long, so eat those first.

New potatoes can be harvested earlier in the season, right after the plants flower. These young, thin-skinned potatoes should not be confused with the smaller reddish kinds of mature potatoes identified in stores as "new potatoes."

True new potatoes are harvested from green plants. They are high in water and low in starch, which makes them a favorite for cooking. Be sure to eat them right away as they do not preserve, store, or travel well.

I'm Faith Pirlo.

Jessica Damiano wrote this article for the Associated Press. Faith Pirlo adapted it for Learning English.

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stress — v. to feel very worried or anxious about something : to feel stress

mature — v. or adj. to grown or developed; fully grown or developed

rub — v. to press your hand or a cloth on a surface and move it back and forth

shovel — n. a tool with a long handle that is used for lifting and throwing dirt, sand, snow, etc.

preserve — v. to keep something the same or prevent it from being damaged or destroyed

flavor — n. the taste of something

starch — n. a substance that is found in certain foods (such as bread, rice, and potatoes)