The white potato is distinctively a cool-season crop. On the average the best yields are secured by planting early in order to get the crop as far along as possible in advance of the high summer temperatures.
The heaviest yields, on the average, were secured from the plantings made shortly after the seasonal rise in temperature crosses the 40° line.
For central Iowa, this period is usually reached during the first half of April.
In a date-of-planting-in-relation-to-yield experiment with late potatoes, covering six years, the results were as follows:
The average of the April plantings was 124.4 bushels per acre and for the June plantings, 76.2 bushels.
The planting dates covered by the last week of April and the first two weeks in May averaged about the same.
The plantings made after the middle of May gave a successive decline in yield.
Between the first and last planting there was a spread of 65.8 bushels per acre.
The minimum vegetative temperature for corn is fully ten degrees above that for potatoes. The general practice of planting late potatoes after corn planting is contrary to the temperature requirements of the two crops, and is regarded as one of the important reasons for the decline in potato yields in Iowa.
In general, the early market is the most profitable. Early planting and early marketing go hand in hand.
The danger from frost injury at harvest time may be largely eliminated by early planting.
Erwin, A. T. and Rudnick, R. A.
"Potato growing in Iowa as affected by temperature,"
Bulletin: Vol. 17
, Article 1.
Available at: https://lib.dr.iastate.edu/bulletin/vol17/iss206/1