Ask a Master Gardener: What’s the difference between determinate and indeterminate potatoes?

Although St. Patrick's Day is the traditional day to plant potatoes, Mid-Missouri weather usually does not cooperate and this year was no exception -- at least not in my garden.

There have not been too many years I have been able to meet that deadline. So I usually try to get mine in the ground at least by Good Friday. The ideal time frame for our area is March 20 through April 10, which happens to encompass Good Friday this year. The way our weather is acting, I hope it will dry out by then.

Now might be a good time to start looking for seed potatoes since it is a good idea to place the seed potatoes in a bright warm spot about a week before you want to plant. This will help break the spuds' dormancy and assure they will grow quickly when you put them into the still-cool spring soil.

A couple of years ago I found out about "determinate and indeterminate" potatoes. I had always heard about determinate and indeterminate tomatoes, but I had never heard of potatoes having these characteristics.

I am not sure how I missed this in 50 years of gardening, but sure enough, determinate potatoes are varieties with tubers that grow in just one layer. Because they are going to be on just the one layer, the plants do not require mounding the soil around them. These potatoes, sometimes called "early potatoes," are usually determinate and are ready in about 70-90 days.

Indeterminate or late season potatoes on the other hand grow in multiple layers, so it is important to mound soil around the plants.

This will give you a better yield. Indeterminate potatoes produce late crops in about 110-135 days.

To grow determinate potatoes, sow them in loose soil to a depth of about 4 inches. Use mulch to prevent weed growth and to prevent the tubers from being exposed to the sun, which can cause the tubers to turn green and somewhat toxic. Some varieties of determinate potatoes are Norland, Fingerling, Yukon Gold, and Superior.

To grow indeterminate potatoes, start by covering them with 6 inches of loose soil. When the plants have reached about 6 inches high, add several inches of soil, straw or dead leaves until there is just about 2 inches of the plant sticking up. Continue adding layers as the plant grows.

Because of the multiple layers of tubers with indeterminate potatoes, these varieties are well suited to potato boxes, towers or other vertical means of growing. These are good for small spaces because they allow you to grow up and still get a good yield of potatoes. Some varieties of indeterminate potatoes are Snowden, Russet Burbank, Bancock Russet and the ever popular Kennebec.

This explains why I have never had much luck with a potato tower or other containers. I almost always grow early potatoes for two reasons; first is that I am not as patient as I should be when waiting for produce. And second is because potatoes do a little better maturing in cooler weather and you can't always trust Mid-Missouri weather to stay cool for long in the early summer.

If you are planting indeterminate potatoes, a day or two before planting, use a sharp, clean knife to slice the larger seed potatoes into "seed pieces." Each piece should be approximately 1- to 2-inch pieces and must contain at least two "eyes" or buds. Smaller potatoes may be planted whole.

In the next day or so, your "seed" will form a thick callous over the cuts, which will help to prevent it from rotting once planted.

For potatoes to grow best, they need plenty of sunshine and loose soil. Work some compost or other garden conditioner into the garden bed. Adding compost will give the tubers a good start. Dig a shallow trench about 4 inches wide and 6-8 inches deep. The spacing at which you place the seed pieces will determine the harvested potato size.

Plant your potato seeds 12 inches apart in this trench. Place the potato pieces into the trench (cut side down) and then cover them with 3-4 inches of soil. (Do not fill the trench in completely!)

Depending on the soil temperature, the sprouts will begin to emerge in about two weeks. At this time, add another 3-4 inches of soil.

When the stems are about 8 inches high, you once again add enough soil to bring the level half way up the stem of the plant. Another "hilling" will be needed 2-3 weeks later, at which time you again add soil halfway up the stem of the plant. Add enough soil to ensure there is enough soil above the forming potatoes that they don't push out of the hill and get exposed to light.

I hope this information will be helpful as you pick this year's variety of potatoes to plant.

Happy gardening.

Peter Sutter is a lifelong gardening enthusiast and a participant in the MU Extension's Callaway County Master Gardener program. Gardening questions can be sent to [email protected].