If you're hoping to grow the biggest potatoes possible this summer, try adding more calcium to the soil. Researchers at the University of Wisconsin in Madison grew 'Russet Burbank' potatoes in test plots with supplemental calcium fertilizer. They fed plants 3.5 pounds per 1,000 square feet of either calcium nitrate or calcium chloride split equally over four treatments and applied at 4-, 6-, 8-, and 10-week intervals after planting.
The results were fewer but larger tubers in the test plots when compared to the control plots, which received no calcium supplementation. The overall yield in both calcium-amended plots was the same.
To make sure your soil has enough calcium, test the soil early in the season. If your soil is deficient, incorporate a calcium fertilizer, such as gypsum, before planting.
For more information on this potato fertilization research, contact the University of Wisconsin.