Frequent heavy rains continue to challenge some Idaho potato growers as they plant the state’s iconic crop.

“Around here, it is behind around a week,” Brett Jensen, who farms in the Idaho Falls-Hamer, said April 8. “Right now, the soil temperatures are still really cold, and we are supposed to have rain and snow this week. So we are definitely behind around here.”

Jeff Gibson, who farms near Paul in the state’s south-central region, started planting April 8 but was stalled by weather the next day.

“We can’t go today because of the downpour here right now,” he said early April 9. “It’s just a very wet spring. It’s muddy, and you can’t get into the fields.”

Planting in the south-central region is on schedule in comparison to the average year, Gibson said. “It’s about the usual timing. It’s just what the weather will let us do from here on out.”

Potato planting equipment, crews and the seeds themselves cannot operate at peak efficiency when soils are too wet and compacted. Persistent cold, wet conditions can delay completion of planting and ultimately reduce yield because the crop is exposed to fewer total days of ideal growing temperatures.

“This has been fine for us. We are right on schedule,” said Doug Gross, who farms near Wilder, on the state’s western edge. He expected to finish planting around April 10, early compared to average.

Soil temperatures have been good, as have moisture levels, he said. Seed quality is excellent.

“A lot of our ground this year happened to be sandier soils, so it worked out,” Gross said. “We had 50-degree soil temperatures, so we went ahead.”

Seed should be planted when soil temperatures are at least 48 degrees, said John Taberna, soil scientist and owner at Western Laboratories in Parma. Colder soils increase the risk of seed rot, and of poor stands post-emergence. Potato seed is strong, producing a hearty stem equipped to break through soil crust effectively.

Heavier soils, with more silts and clays, are found in many growing areas in the state’s south-central and eastern regions, he said. These growers must wait longer after rain before they can work the ground compared to those who farm sandier soils. Potatoes in both soil types are harvested around the same time, ahead of the first freeze.

Gibson, whose farm usually plants over a 14- to 20-day period depending on weather, said seed planted in cold soil grows more slowly and takes longer to emerge. When emergence or planting in general are late, plants are exposed to fewer ideal growing-degree days and are more prone to produce lower yield, especially if the farmer does not want to take on the risk of delaying harvest.

“What reduces the yield is if we get held back planting and then get a Sept. 1 frost,” he said.

Jensen said he likely will start planting around April 20 and finish about May 10. Most years, he aims to start on about April 12 and finish in the first few days of May — ideally, the first day of the month to maximize growing-degree days through the season.

His eastern Idaho farm is just above 4,000 feet in elevation.

“Where we are, we can’t push the harvest date back because of the potential for cold weather,” Jensen said.

Taberna said potato planting likely won’t approach late status unless it begins in the last 5 to 10 days of April.

“In Idaho, we are still in good shape,” he said.

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