an image of a potato cut in half showing the brown cavity of hollow heart inside

Can Potatoes Grow Too Big: why massive potatoes (tubers) should be avoided and how to keep their growth in check

Potatoes come in a variety of shapes and sizes, from tiny fingerlings to massive baking potatoes. The size of the mature potato tubers depends primarily on the type of potato you are growing, but other factors also affect their size. While many gardeners face the challenge of potato tubers that grow smaller than expected, sometimes potatoes that are too big become an issue.

Can potatoes grow too big? 

Yes, although under normal growing conditions, most potatoes will grow to their average expected size and shape, sometimes potatoes will experience a fast spurt in growth which leads to them growing abnormally large in a short period of time. This typically happens when they receive uneven watering or after large applications of fertilizer.

When your potatoes are maturing, a sudden period of rain (or increased watering from you) or a large application of fertilizer can result in a sudden burst of growth and cause the tubers to become overgrown. Large potatoes aren’t always a problem, but oversized potatoes often develop “hollow hearts”, also known as being “boast” in the middle.

What is hollow heart in potatoes?

When potatoes undergo a rapid growth spurt, usually from increased water or fertilizer the tuber enlarges rapidly in a short period of time, and the center of the potato becomes hollow. Hollow heart looks like a star-shaped hole in the center of the potato. It may have brown edges, but the rest of the potato flesh is crisp and white.

Hollow heart in a potato (image from ADHB agriculture)

Hollow heart indicates that your potato grew so quickly that it split apart in the center. In oblong potatoes, you may find two hollow hearts.

Hollow heart does not affect the flavor of the potato and is not a sign of disease.


Why should oversized potatoes be avoided?

Oversized potatoes are more likely to have hollow hearts, making them unsuitable for making chips, french fries or serving as baked potatoes. However, potatoes with hollow hearts can be used for mashed potatoes, in soups and stews, and even cut to make home fries.

If the hollow heart has brown edges, trim away the brown and use the potato as desired. Hollow heart does not affect the nutritional value of the potato and does not change the flavor.

What causes potatoes to grow excessively large?

Potatoes that have been stressed from lack of adequate water that suddenly receives an abundance of water tend to grow rapidly and may become overgrown. Similarly, large applications of fertilizer will cause potatoes a massive growth spurt which can also lead to hollow heart forming. Although excessive Nitrogen causes large tops to form and not large potatoes – if a large application of potato fertilizer high in P and K is applied this will increase the risk of hollow heart considerably.

How close together you plant your potatoes also affects how large the tubers grow. If you want smaller tubers, space your potato plants 8 inches apart in rows. Spacing potatoes too far apart increases their size.

How do I check if my potatoes are big enough?

Tiny new potatoes begin to grow at about the same time the potato plants bloom. Within 2 to 3 weeks, the tubers are large enough to harvest as ‘new potatoes.’ However, it will take weeks for your potato tubers to reach full size.

To check the size of your potatoes, gently remove the soil around the base of the plant with your hands. Dig down until you reach the roots of the potato plants. Potatoes form in clusters under the plant. If the potatoes are too small for your needs, gently cover them with the soil and let them grow for another week or two before checking again. Alternatively, you can harvest a few small potatoes now and recover the roots to allow more potatoes to grow.

The days to maturity of your potatoes will give you a good indication of when they will mature. Check them a week or two before their expected maturity date.

Mature potato plants begin to turn yellow, fall over, and eventually turn brown when the potato tubers are mature. If you notice your potato plants are dying back naturally the potato tubers should be mature.

How can I stop my potatoes from growing too big?

If your region has sporadic rainfall perhaps you can choose a variety that avoids problems with hollow heart. Ensure you plant as close as recommended and apply fertilizer in small doses spaced evenly throughout the year.

Water your potatoes once or twice weekly to keep the soil from drying out completely throughout the growing season. One of the most common issues with poor potato yield and misshapen and overgrown potatoes is uneven watering.

Resist the urge to let your potatoes go for weeks with inadequate water and then water them frequently because they are not doing well. Watering consistency is the key to growing well-shaped and healthy potato tubers.


Can I stop my potatoes from growing without using chemicals?

Yes, if you see that your potatoes are already large enough you can remove the green plant foliage away from where the potatoes are grown. Once the tops have been removed the potatoes will stop growing and being to set their skins for harvesting.

If you are eating your potatoes fresh from the garden, usually there is no need to stop the plants from growing as you can harvest the tubers whenever they reach the size you prefer.

 If you wish to store your potatoes for winter use and the tops have not died back naturally, the University of Minnesota Extension recommends checking the skins to see if they are mature. If the skins rub off easily with your thumb, they are not mature, but you can take care of that by curing them.

To cure the potatoes, place them in a dark, well-ventilated area with temperatures between 60- and 65-degrees Fahrenheit for at least ten days. This causes the skins to thicken and wounds to heal.

Why do potato farmers use chemical sprays to kill the potato foliage?

While farmers and large-scale potato growing operations often use chemical sprays to kill the foliage, it is done primarily for ease of harvest, although sometimes it is used initially to stop the potatoes from growing any larger. If the foliage is dead, the potatoes stop growing and it is easier to harvest the potatoes mechanically using potato harvesters. In the home garden, killing the foliage is unnecessary as you can pull up the plants by hand and harvest the potatoes with a hoe or other garden tools.

Killing the foliage once the potatoes are mature is unnecessary as the potatoes will stop growing on their own. Killing the foliage when the potato tubers are mature does not affect the size, flavor, or maturity of the potato tubers.

Summary

Choosing a potato variety that suits your climate/region and which will produce potato tubers in the size and shape you prefer is the first step to preventing growing tubers that are too big. Pay attention to how far apart you plant your potatoes so they don’t have too much room to grow massive. Finally, try to avoid large applications of water or fertilizer they receive to help prevent issues with large tubers with a hollow heart.