When is it Too Late to Plant Potatoes? (Plus Planting Dates)


If this is your first year planting potatoes, or if you got a late start on your garden, you might be wondering if the time for planting potatoes has passed.  After all, you don’t want to put in the effort to plant a crop of potatoes that won’t grow well.

So, when is it too late to plant potatoes?  Most gardeners should plant potatoes by the end of May for a spring planting.  This allows enough time for the potato plants to grow and mature before the cooler weather (and potential frost) in the fall.  Plant well before soil temperatures reach 80 degrees Fahrenheit (27 degrees Celsius), since tubers will stop forming if it is too warm.

Of course, if you live in a very warm climate, you may be able to plant mid-season and late season potato varieties in the fall to get a second harvest later in the year.

If you live in a cold climate, you can extend the growing season with a greenhouse or row covers to protect against frost at the end of the season.

There are many factors that determine when you can plant potatoes, including frost dates or the type of potato and its time to maturity.  Let’s take a closer look at some of these factors.

When is it Too Late to Plant Potatoes?

To determine when it is too late to plant potatoes, there are 3 main factors to consider:

  • Variety of Potato (determines time to maturity)
  • Last Frost Date (cold temperatures in the fall will kill potato plants)
  • Desired Harvest (new potatoes, mature potatoes, large potatoes)

Let’s start by looking at the different types of potatoes you can choose to grow.

sprouting potatoes
Usually, you plant pieces of sprouted potatoes (seed potatoes) in the spring.

Variety

The variety of potato you choose will play a big part in determining when to plant your crop.  The variety you choose will determine the time to maturity for your potato plants.

The time to maturity (or days to maturity) is the number of days it takes for a potato plant to grow into a mature plant and produce tubers that you can harvest.

According to Fedco Seeds, potatoes can be classified in 3 different groups, depending on the time to maturity:

According to the University of Illinois Extension, you can plant early season, mid-season, and late season potatoes in the spring.

Avoid planting potatoes when the ground is still wet from heavy spring rains.  Otherwise, or they may rot before they grow!

Planting too early in the spring may also expose your potato plants to frost, which can kill them or set them back (more on this later).

If it is too late to plant in the spring, you can plant mid-season and late season potatoes as late as July 1st – as long as you live in a mild climate.  If you want to store your potatoes over the winter, late season potatoes are the best option.

Frost Dates

The first frost date in the fall will also tell you if it is too late in the season to plant your potatoes.  There is a 30% chance that no frost will occur before the first frost date (or first fall frost date).

For example, in Boston, MA, the first fall frost date is November 3.  This means that there is a 30% chance of getting at least one frost before November 3.  It also means that there is a 70% chance that no frost will occur before November 3.

Last frost dates will vary widely depending on where you live.  For example, the last frost date in Montpelier, Vermont is September 24, while the last frost date in Atlanta, Georgia is November 13.  In Miami, Florida, frost is very rare, and may not occur for years on end.

Before you decide whether it is too late to plant potatoes, use this tool from the Old Farmer’s Almanac to find the last fall frost date in your area.

Desired Harvest

Depending on the size of potatoes you want at harvest, you might be able to get away with planting a little bit later in the year.

New Potatoes

If you are hoping for new potatoes (small, less mature potatoes with thin skins), then you can harvest them 2 to 3 weeks after the plant stop flowering.  Not all potato plants will flower, so you may need to dig in the ground every once in a while to see how they are growing.

According to the University of Maryland, you can harvest new potatoes 6 to 8 weeks (42 to 56 days) after planting.

Mature Potatoes

Mature, full-size potatoes have thicker skins, and they take longer to grow than new potatoes.  Basically, you let new potatoes grow for a bit longer so they can mature fully and get bigger.

potatoes in basket
Mature potatoes are larger than new potatoes, but they take longer to grow.

Mature potatoes will be ready for harvest 2 to 3 weeks after the foliage on the plant dies back.  If you plant late in the season, there will be less time for the potatoes to grow.  As a result, you will get smaller potatoes on each plant and fewer potatoes in total.

Summer heat with soil temperatures over 80 degrees Fahrenheit (27 degrees Celsius) will stop tubers from forming.  On the other hand, fall frosts will kill the plant and stop growth.

When to Start Your Potato Plants

You can use the factors mentioned above to figure out when it might be too late to plant your potatoes.  For example, let’s assume that:

  • you live in Boston, MA
  • you want to plant a late-season potato variety, such as Princess Laratte
  • you want to harvest mature potatoes (not new potatoes)

We know that the last frost date in Boston is April 10.  We also know that Princess Laratte potatoes take 90 to 110 days to mature.

Let’s say that we are planting a week late, and we wait until April 17 to plant our potatoes.  Working forwards from April 17, we can see that the potatoes would be mature on July 16 at the earliest (13 days in April, 31 days in May, 30 days in June, and 16 days in July, for a total of 90 days).

For a spring planting, you can plant potatoes as soon as ground can be worked (that is, when it thaws out).  However, remember that potatoes will not grow until the ground is at least 45 to 50 degrees Fahrenheit (7 to 10 degrees Celsius).

When planting, the soil should be moist, but not wet.  Wet soil will cause potatoes to rot before they can grow.

According to the Old Farmer’s Almanac, you can take a chance and plant potatoes 6 to 8 weeks before the last spring frost date in northern regions.  These crops will mature earlier in the season, but there is more risk of late spring frosts damaging or killing the plants.

Especially in cold northern regions, it is safer to plant your potatoes any time in the week or two before the last frost date.

If you want to learn more about how to plant your own sprouted potatoes, you can read my article all about it here.

How to Protect Potato Plants from Cold

Potato plants are a cool weather crop, so they can tolerate some cool temperatures.  In case of a late spring frost or early fall frost, here are a couple of ways you can protect your potato plants from cold.

Greenhouse

The soil in a greenhouse will get warm enough for planting potatoes much sooner than the soil outside.  You can also control the amount of moisture in the soil inside your greenhouse.

You can even choose to plant potatoes in containers inside your greenhouse if you wish (you can even try planting potatoes in a straw bale!)  For more information on growing potatoes in straw bales, you can read my article here.

greenhouse
A greenhouse will help to keep your potato plants warm and protect them from fall or spring frosts.

If you plant your potatoes a little late, you can use a greenhouse to extend the growing season and protect your potato plants from fall frosts.

Row Covers

You also have the option of using row covers to protect potato plants against late spring or early fall frosts.  Row covers are made from fabric, and they protect plants from cold (and insects), while also allowing sunlight to get through.

One brand of row cover with varying levels of protection is Agribon.  For example, Agribon AG-50 offers 6 degrees of frost protection (down to 26 degrees Fahrenheit).

What Happens if You Plant Potatoes Too Late?

If you plant your potatoes too late, you will have problems with heat in the summer or with cold in the fall.

Summer Heat

The first problem you will have when planting potatoes too late in the summer is the heat.  Potato plants may stop producing tubers if the soil is too hot.

Higher temperatures and brighter sunlight also cause soil to dry out faster.  Remember that young potato plants are not yet established with strong roots.

That means you will need to work harder to give them enough water.  This can be a big chore in a large garden.

Fall Frost

Even if you manage to deal with the summer heat, you still need to worry about frost in the fall.

A hard frost will kill potato plants, and an early fall frost will stop the plants from growing larger tubers.  If the ground freezes, it will be difficult to harvest your potatoes without damaging them (if you can get them at all!)

Conclusion

Now you have a better idea of when it is getting too late to plant potatoes.  You also know a little more about how to protect your potato plants from frost, if necessary.

I hope you found this article helpful – if so, please share it with someone who will find the information useful.

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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