The 3 Reasons Why Potatoes Develop Brown Spots Inside

Cutting up potatoes and running into brown spots is a normal part of preparing these vegetables, but have you ever paused and wondered why they form in the first place? You can cut them out easily enough, but where do they come from? Let’s find out the answer to why are my potatoes brown inside?

Brown spots inside a potato can be formed by something called rust, or by stress when the tuber is growing. Sometimes, specific fungi or viruses can cause the formation, and occasionally, a hollow ringed by brown flesh can be caused by uneven watering.

As you can see, quite a lot of different things can cause brown spots to appear inside a potato, so let’s explore what factors may be at play and whether these make the potato unsafe to eat.

What Is Potato Rust?

Internal rust spots are small brown spots that appear on the inner flesh of the potato. There are usually many of them and they are dark or slightly reddish-brown. They may appear in clusters or be spread throughout the potato.

potato rust

These spots can be caused by poor soil, and are most likely to form if the potatoes are short on potassium and lime. Some types of potatoes are more resistant to rust than other kinds, but any sort can develop it if the conditions are bad enough.

Does Stress Cause Brown Spots?

If the plant is very stressed while forming its tubers, brown spots are more likely to develop in the flesh. These will be small in most cases, but severe stress could form bigger spots.

Stress will usually be the result of unsuitable growing conditions, so make sure you are providing the potatoes with everything they need if you are growing them at home. Think about water, soil condition, light, and space, and plant your potatoes accordingly. Make sure you rotate your crop each year to reduce the risk of the soil getting depleted.

What Is A Potato Virus?

In some cases, brown spots can be caused by viral or fungal infections. There are quite a few of these – and that might leave you concerned about whether the potato is safe for you to eat, or whether it will make you sick.

Fortunately, these viral and fungal infections are not harmful to people, and will not hurt you if you consume them. They are specific to potatoes and will only attack the flesh of the tuber. They should not spread to other crops outside the potato family, either.

What Impact Does Uneven Watering Have?

Uneven watering can also cause your potatoes to develop brown spots, and if you’ve bought some from the store which contain these, it’s likely that the crop was not well looked after, or that the summer was particularly hot and it was difficult to maintain good levels of water in the soil.

Often, underwatering or overwatering a potato plant will result in the tubers developing something known as hollow heart. This is a gap in the potato’s flesh in the middle of the fruit, which is sometimes ringed with brown (although sometimes it is plain white).

hollow potato

This usually occurs when the plant is underwatered, causing slow growth, and then watered heavily, speeding the growth up suddenly. The inside of the tuber splits as a result of the sudden growth, leaving a hole in the center. This split may form brown edges as the potato continues to develop.

Some big potatoes may even form more than one of these holes, although most will only have one. Consistent watering should help to reduce the risk of hollow heart forming.

Can Pests Cause Brown Spots?

There is also an insect called the potato psyllid that can cause potato browning. This insect will damage the plant, rather than directly impacting the potato; it is a sapsucker and will eat away at the plant’s tissues. The insect carries a kind of bacteria that will affect the plant, too, and this will cause stress that will make the potato turn brown inside.

Of course, other insects burrowing into the potato can also cause brown spots, but they will leave holes in the outer skin, so you should be able to determine that insect damage is responsible in these cases.

Are Potatoes With Brown Spots Safe To Eat?

With that many possible reasons behind brown spots, you might be wondering how you can tell if the potato is safe to consume – because it will often be impossible to work out which of the above things caused the brown spots. 

Fortunately, almost all of these potential causes of damage will not make the rest of the potato’s flesh dangerous to cook and eat; they are all fairly harmless, including the virus. You can use a sharp knife to cut the brown out of the potato. Cut off any particularly heavily spotted areas and discard them, and only use the clean white bits of the potato.

This will usually work and will prevent you from wasting potato that is still good to consume. However, with heavily marked potatoes, you should take a little more care. Look at:

  • Does the potato smell okay?
  • Is the flesh around the brown area mushy or slimy?
  • How far has the brown area spread through the potato?
  • How old is the potato?

If you aren’t sure, it is better not to consume a brown potato, as it could make you sick. A few brown specks will almost always be fine, but be wary if the potato is old, filled with brown marks, or has a strange smell when you cut into it. A slimy texture is also a sure sign that the potato is no longer safe to eat.

Conclusion

A whole range of different things can cause brown spotting inside a potato and it is normal to come across small brown spots when you are preparing these vegetables, especially if you have grown the potatoes yourself.

Commercial potatoes are less likely to have brown areas but may do in some cases. Fortunately, you can usually cut the brown parts out and use the rest of the potato.

Alexandre Valente

Hey there! My name is Alex and I've been vegan for more than five years! I've set up this blog because I'm really passionate about veganism and living a more eco-conscious life. Hopefully, I can use this website as a channel to help you out on your own journey!

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