Potato Eyes & Sprouts (7 Common Questions Answered)


The eyes (or buds) on a potato tuber will eventually sprout and grow longer.  If planted, a sprouted tuber will grow into a new potato plant.

So, what do you need to know about potato eyes and sprouts?  Potato eyes will sprout & become a new plant.  Potatoes sprout fast (in 2 weeks) at room temperature (70 degrees Fahrenheit or 21 degrees Celsius).  Put long sprouts in light to slow their growth.  Remember: plant tubers with eyes facing up, and hill the plants as they grow!

Of course, some store bought potatoes are treated with a sprout inhibitor called clorproham.  This chemical will slow down or prevent a tuber from sprouting, and the resulting plants may not grow as vigorously.

In this article, we’ll take a look at potato eyes and sprouts.  We’ll answer some common questions about them and why you should hill your potato plants during the growing season.

Let’s get started.

Potato Eyes & Sprouts

Potato tubers are not roots, but rather modified stems.  These modified stems are used to store energy (in the form of carbohydrates).

potatoes clean for storage
At first, you can barely see the eyes (buds) on potatoes before they start to sprout and grow longer.

Potato tubers have eyes on them, which are really just small buds waiting to grow.  To be honest, potato eyes don’t look like much at first.

However, if you give potato eyes enough time in the right conditions, they will start to sprout.  These sprouts get longer and will eventually become the stems of potato plants later in the growing season.

This raises the question of what to do with the sprouts before planting.  Should you cut them off, shorten them, or leave them on?  Let’s discuss that first.

Can You Cut The Sprouts Off Potatoes Before Planting?

You can cut some of the sprouts off a potato before planting, but don’t remove them all!  The sprouts (which grow out of the eyes of a tuber) will eventually grow up out of the soil and become the stem of a new potato plant.

sprouted potato
You should leave some of the sprouts on a potato plant, but you can cut some off if there are too many.

Removing all of the sprouts will set back a potato plant’s development.  The tuber will need to sprout again in order to grow into a full-fledged potato plant.

Remember: the potato tuber has to use up some of its stored energy (carbohydrates in the form of starches) to grow each sprout.  Cutting off the sprouts will waste that energy!

However, you might consider cutting off some potato sprouts if there are way too many.

According to the University of Maine Extension, a planted potato with fewer sprouts will produce fewer but larger potatoes at maturity.

If you wait too long and a sprouted potato gets too old, the sprouts will start to look hairy.  You might even see small tubers start to form at the ends of the sprouts.

In that case, you will not get strong plants from the sprouted tubers.  Instead, use younger sprouted potatoes to get healthier plants with higher yields.

Do Potatoes Need To Sprout Before Planting?

Potatoes do not need to sprout before planting.  Given enough time, they will still sprout underground and grow into new plants.

However, sprouting potatoes before planting does have some advantages.

First of all, you will only be planting potatoes that you know are viable.  The ones that have already sprouted are ready to grow into new plants.

sprouted potatoes
If you wait for your potatoes to sprout before planting, you will know that they are viable and can grow into a healthy plant.

By waiting for potatoes to sprout, you can avoid planting “duds” that may not grow very well.  Store bought potatoes are more likely to sprout poorly (or not at all), since they are often treated with a sprout inhibitor called clorproham.

The second advantage of planting sprouted potato tubers is an earlier harvest.  Sprouting your potatoes before planting gives them a little bit of a head start on growth.

It can take some time for potatoes to sprout underground, especially if the soil is cool.  Giving them the perfect conditions indoors will speed up the process and save you some time.

How To Make Potatoes Grow Eyes (Sprouting Potatoes)

There are several factors that control when the eyes on potatoes will start sprouting.  The important factors are:

  • Temperature
  • Humidity
  • Light
  • Dormancy (rest period)

Let’s take a closer look at each one.

Temperature

Cooler temperatures are better for storing potatoes to prevent sprouting.  Keep potatoes cool if you need to wait until the growing season gets closer.

However, you should never freeze potato tubers.  This will damage them and prevent them from sprouting and growing into new plants.

To encourage potatoes to sprout, warm them up to room temperature, or around 70 degrees Fahrenheit (21 degrees Celsius).  Do this about 2 weeks before planting (5 weeks before the last spring frost date).

You can find the last spring frost date in your area on this page from the Old Farmer’s Almanac.

Pinterest How To Successfully Plant Potatoes That Have Sprouted
Leave potatoes at room temperature for a couple of weeks to encourage them to begin sprouting.

For example, the last spring frost in Boston, Massachusetts in 2021 is April 10.  Working backwards 5 weeks (35 days), we get a date of March 6 (25 days in March + 10 days in April = 35 days).

So, if you want to plant potatoes on March 20 (3 weeks before the last spring frost date), then start warming up the tubers on March 6 (5 weeks before the last spring frost date).

This will give the potatoes 2 weeks at room temperature to start sprouting.

Humidity

It may seem counterintuitive, but potatoes do not like to be stored in extremely dry conditions.  In fact, potatoes will wither and dry out if you store them in a low humidity environment.

This withering and drying may prevent sprouting later on.  Instead, store potatoes in high humidity to keep them fresh.

The University of Maryland Extension suggests storing potatoes in conditions with 90% relative humidity, at 40 to 50 degrees Fahrenheit (4 to 10 degrees Celsius) where they can keep for 6 to 8 months.

Light

Potatoes do not need light to sprout.  Normally, potato tubers left underground over the winter will sprout on their own in the spring – without ever seeing the sun.

The University of Maryland suggests that exposing potato tubers to light will help to keep the sprouts short.  This may be useful if they start to sprout earlier than you expected, or if they start to get too long.

Remember: if you plan to eat your potatoes, you should not leave them in sunlight.  When potatoes are exposed to sunlight, they will turn green (due to chlorophyll) and they may become toxic (due to solanine).

green sprouted potato
Potato tubers left out in sunlight can turn green & toxic, due to chlorophyll and solanine.
Image courtesy of user:
Olybrius via:
Wikimedia Commons: https://commons.
wikimedia.org/wiki/File:
Evil_green_potato.jpg

You can learn more about why potatoes turn green & toxic (and how to prevent it) in my article here.

Dormancy

Potatoes need a time of dormancy (or a “rest period”) before they will sprout.  This dormancy period prevents a potato tuber from sprouting at the wrong time.

For example, if a potato sprouts in late fall or winter, the plant will have little or no chance to survive once it breaks the soil surface.

frost on grass
Potato plants will die back to the soil surface if a hard frost comes along.

This is why you usually won’t be able to get a newly harvested potato to sprout right away.

According to the Texas A&M University Extension, cool temperatures or very warm temperatures can both break the dormancy period for potatoes.

As mentioned earlier, a couple of weeks at room temperature (after a dormancy period) is usually enough to wake up potato tubers and encourage them to start sprouting.

How Long Does It Take For A Potato To Sprout?

After a period of dormancy, a potato may sprout in as little as 2 weeks at room temperature (70 degrees Fahrenheit or 21 degrees Celsius).

However, store bought potatoes are often treated with the sprout inhibitor clorproham.  This will increase the time it takes a potato to sprout, even in warm temperatures.

russet potatoes
Store bought potatoes are often treated with clorproham (a sprout inhibitor). This makes it difficult to sprout them for planting.

To get your potatoes to sprout faster, use certified disease-free seed potatoes.  According to the University of Oregon Extension, these seed potatoes are specifically bred for growing new plants, and they are never treated with sprout inhibitors.

How Long Should Potato Sprouts Be Before Planting?

The Colorado State University Extension suggests that potato sprouts should be 1 inch long (or less) at planting time.  We are really just waiting for potato sprouts to ensure their viability, rather than to get long sprouts for planting.

If the sprouts on a potato are too long, it will be more difficult to plant the tuber without damaging or breaking off the sprouts.

potato with long sprouts
This potato’s sprouts are way too long, and it will be hard to plant it without damaging them.

The potato may also use up too much energy on long sprouts.  This could make it difficult for the sprouts to break the soil surface after planting.

If you see a potato starting to shrivel up, then it is using a lot of its stored energy to produce sprouts!

Don’t worry if your potato sprouts too early, or if the sprouts start to get long.  According to the University of Maryland Extension, you can expose sprouts to sunlight to slow down their growth.

When Planting Potatoes, Do You Put The Eyes Up Or Down?

When planting potatoes, the eyes should face up.  The eyes (or sprouts) will eventually grow up and break through the surface of the soil.

It will be easier for them to do this if they are facing up.  If a sprouted potato has sprouts or eyes on both sides, then you can cut it into two or more pieces before planting.

cut russet potato with eyes
You can cut a large sprouted potato before planting so that there is one eye per piece.

However, make sure that each cut potato piece has at least one eye.  Also, don’t make the pieces too small, or they won’t have enough energy to grow into a healthy potato plant.

The Colorado State University suggests that potato pieces should be 2 to 3 ounces after cutting.

If you do choose to cut a sprouted potato into pieces, use a clean knife between cuts to avoid spreading disease (clean the knife with rubbing alcohol).  Also, leave the cut pieces in a dark room for 4 to 7 days to encourage a callus (scar tissue) to form over the cut part of the potato.

This callus will help to prevent diseases after planting the cut potato pieces.

How Deep To Bury Potatoes?

You don’t need to bury potatoes very deep.  According to the University of Illinois Extension, you can plant sprouted potatoes at just 1 to 3 inches deep.

However, this is not the whole story!  As the season progresses, the potato sprouts will break the soil surface and form tall stems.

Sometimes, potato tubers will form near the stems at or above the soil surface.  As mentioned earlier, this can cause green potatoes that turn toxic when exposed to sunlight.

To prevent this problem, use hilling throughout the growing season.  Hilling means piling up soil (or mulch, such as straw) around the base of the potato plant as it grows.

rows of potatoes
Hilling prevents potato tubers from turning green and toxic.

In addition to preventing green and toxic potatoes, hilling also has some other benefits for potato plants:

  • It provides stability for the base of the stems, which prevents the potato plant from falling over as it grows taller.
  • It smothers existing weeds and prevents new weeds from growing near the potato plant, reducing competition for water and nutrients.
  • It protects the plant from damage caused by a late spring frost or early fall frost.

You can learn more about hilling potatoes (and why you should do it) in my article here.

potato plants in straw
You can use straw or other types of mulch for hilling potato plants.

You can also learn more about how deep to plant potatoes in my article here.

Conclusion

Now you know a lot more about potato eyes and sprouts.  You also know the answers to some common questions about sprouting potatoes.

You can learn more about planting sprouted potatoes in my article here.

You can eat sprouted potatoes in some cases, if you take the proper precautions – you can learn more in my article here.

You can learn about why potatoes turn black in my article here.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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