Why Do Potatoes Turn Black?

When potatoes turn black it can occur for a variety of reasons. It also makes a difference whether the potatoes are raw or cooked, whether they have not yet been harvested and even what kind of a knife you cut them with. In some cases “black” is a bit of a misnomer – they’re more of a dark brown.


Blue Potatoes

Some potatoes are naturally dark on both the outside and inside. The internal color varies from a dark blue to a deep purple, but both can look black in the right light. This is normal and does not affect taste. These potato varieties include:

  • All Blue
  • Adirondack Blue
  • Purple Majesty
  • Magic Molly.

Raw Potatoes

When you cut a raw potato, the flesh is exposed to air for the first time and rapidly begins to darken – apples do something similar. If your knife contains iron, it can also make potatoes darken. The dark color doesn’t affect the eating quality or taste, but it doesn’t look very appealing. To prevent this problem, immediately place cut or peeled potatoes into a bowl of water. Remove to slice or cook. Drain or dry before cooking.

Cooked Potatoes

Potatoes that have been cut and cooked in an aluminum pan may darken from contact with the metal. Aluminum pans – especially the disposable kind – are often thinner than stainless steel or cast iron and may increase risk of burning, which can also turn potatoes black. Potatoes contain iron, which can also cause darkening after cooking.


An otherwise healthy potato may sometimes develop a discolored cavity at its center. This is thought to be caused by excessively rapid growth or sudden temperature changes early in the growing season. Uneven moisture in the soil may also cause hollowheart. The rest of the potato is typically healthy – simply cut out the discolored flesh and eat the rest of the potato.

Harvested Potatoes

If you harvest a potato and it has brown or blackened areas, it may be caused by a fungal problem called blight. In addition to the decayed look, the potatoes will be mushy, inedible and have a characteristic odor. Blight may also show up in stored potatoes. However, if the potato is whole and has no odor but has a blackened area, it may be bruised. Cut out the black area and eat the remainder.

Potato Basics

Potatoes are grown in all USDA Zones. They come in a variety of sizes and shapes as well as different colors. You can plant early, mid-season and late potatoes. All prefer rich, slightly acidic soil that drains well. They need plenty of water while growing and should be kept free of weeds. Harvest new potatoes a few weeks after they flower. The main crop is ready three or four weeks after tops die down.

Text: Garden.eco