It is best to hill within 4 weeks of planting. Be sure to have good soil moisture at planting. If soil moisture is inadequate, lightly irrigate before planting to ensure rapid, early plant growth. Extremely wet soils, however, will increase the possibilities of seed piece rot. An uneven water supply can influence the development of knobs or growth cracks on tubers.
Potatoes have a relatively shallow, sparse root system.
Plants take up most water from the top foot of soil. Irrigate when the soil in this region begins to dry. Check the soil at the plant root zone. If the soil looks and feels moist and forms a wet ball when squeezed by hand, soil moisture is adequate. If the soil forms a fragile ball when squeezed, apply a half inch of irrigation water.