Whatever spacing is used, it should be uniform to ensure uniform size of tubers. Old' potato seed is undesirable because it produces more stems and a larger number of small potatoes than 'young' seed. Seed ages from stresses during the production season, immaturity at harvest, or improper storage and handling. If seed is known to be 'old', spacing should be increased to compensate for the larger tuber numbers produced. Cultivation Potatoes should be hilled or ridged at least once after planting to increase the depth of the seed piece to 4 to 6 inches.
Deep planting is important because tubers only form between the seed piece and the soil surface.
To protect developing tubers from heat and light damage, hills should be flat and broad rather than narrow and peaked. In a clay soil, proper hilling is particularly important because tubers tend to rise to the surface. If herbicides are applied during hilling, care must be taken not to cover the plants with treated soil. The potato has a shallow root system and so should receive a minimum of cultivation to avoid root pruning. Soil temperatures were cooler, soil moisture was higher, and populations of Colorado potato beetle were lower in mulched plots.