Question: 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. 

[![No potatoes image 1](https://i.stack.imgur.com/A8pEG.jpg)](https://i.stack.imgur.com/A8pEG.jpg)

[![No potatoes image 2](https://i.stack.imgur.com/qXDvJ.jpg)](https://i.stack.imgur.com/qXDvJ.jpg)

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.

Answer: 
Judging by the state of the plants when you dug them up, and what the soil surface looks like there are no nutrients whatever in it.

The potatoes *tried* to grow, using the material stored in the tuber, but that's as much as they managed to do. The leaves never developed properly, nor did the roots. They would have grown just as "well" if you had just put them on a concrete driveway and ignored them.

"Purchased humus" doesn't necessarily contain any nutrients. If you really want to grow potatoes in this soil, I would dig the area now to break it up, then spread about a 6 inch depth of horse manure on the surface and leave it for 3 months to let the micro-organisms to break it down and release the nutrients, then dig it in. That might give you better results next year!
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> However, the summer here has been very hot
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This might very well be the reason. Potatoes tend to stop the production of tubers once the soil reaches a certain temperature. Gardeners that plant their potatoes in dark plastic bags and unwittingly put the bags into a sunny spot often have the same problem.

Next year, plant your potatoes as early as possible to get a long growing phase before the summer heat sets in.