Is it ever too late to plant potatoes? Warm days and the availability of vegetable seeds often entice gardeners to think about planting as soon as the weather seems safe to plant different crops.

Planting seed potatoes in early spring is one of the traditional rituals that gardeners look forward to. The questions that gardeners face are about timing, when to start planting, and when it is too late to plant.

Growing up in a family that gardened for years, St. Patrick’s Day was the time to plant potatoes south of Beatrice, Neb. That date was a day of celebration for the holiday, and a tip of the cap to the Irish heritage connected to planting potatoes. As a youngster, I didn’t realize the science behind planting then, and just followed instructions from my parents.

Soil temperature is the key as to when to plant seed potatoes. The minimum soil temperature to plant is 40 degrees F. Colder temperatures inhibit growth, and the seed potatoes die in the ground. Back home, the soil temperature reached that threshold by March 17, reinforcing the famed planting date.

Checking soil temps

There are a couple of ways that gardeners can check the soil temperature before planting. The first option is to use a garden soil thermometer. This inexpensive tool can help pinpoint the soil temperature to decide when to plant various garden crops.

For best results, shove the soil thermometer in the soil 4 inches deep in the same location, at the same time, for seven consecutive days. Wait 15 minutes before recording a temperature reading. Repeat this process over that seven-day period. If the soil temperature is consistent without variation on those daily readings, a consistent temperature can be relied on.

If the soil temperature is not ideal for planting, repeat the soil temperature readings until the 40-degree minimum is recorded for several days.

The other option is to use the updated soil temperature data from the University of Nebraska Cropwatch Soil Temperature Update webpage, found at cropwatch.unl.edu/soiltemperature. A number of weather stations across the state are recording soil temperature data to help producers and gardeners know when to plant crops based off soil temperature.

The key to using this information is to find the weather station closest to your location. Then look for the seven-day, 4-inch soil temperature reading for that weather station. This is the same depth used on a soil thermometer set of readings in a home garden. When the seven-day, 4-inch soil temperature reading reaches the minimum 40 degrees close to where your garden is located, the probability of that minimum soil temperature being safe is fairly high.

This tool is handy in the sense that gardeners do not have to take their own readings, and the temperature data is consistently being recorded for the public to view. While these readings are not the temperature readings from within your own garden spot, it does give gardeners a consistent tool to watch the temperatures in your area of the state.

Is it too late?

To figure how late you can plant potatoes in the season, count the number of days to maturity by cultivar from the first frost date backward. Then you add two weeks to that for the harvest period.

Planting later in the spring can help gardeners miss heavier-than-typical Colorado potato beetle infestations. Some people will plant later with that in mind to miss the beetle population.

You do have to count backward and add the two weeks so there is time for the potatoes to develop, and the plants die back so they can be harvested before the fall freeze to be on the safe side. For more information, email [email protected].

David Lott is a Nebraska Extension horticulture educator based in North Platte, Neb.