I planted red and new potatoes in early May. They were planted 6-8 inches deep. The potatoes were sprouted potatoes from our local hardware store. Our soil is heavy clay but the potatoes were planted in purchased hummus which had been worked into the soil to a depth of about 15 inches. Our climate zone is zone 9B.
As you can see, the potato plants only grew to about 1 ft high. Some of the plants dried up so we started harvesting today (Aug 13). To our surprise, there were no potatoes at all. We watered the potatoes using a drip system (2 GPH) that was set to 15 minutes once per week. However, the summer here has been very hot and whenever the plants looked wilted, we added an additional watering cycle.