Sweet Potatoes

I am trying something new. I have never done this before. I bought a box of sweet potatoes and Costco and some of them sprouted. So I got online and researched growing sweet potatoes. Seems they grow great in Arizona. So, I increased my efforts and wound up with over 15 "slips". I planted them and VIOLA! Now, they have been in the soil for about 12 weeks. I have stopped fertilizing (the nitrogen in fertilizer helps plants grow green lush leaves, and at this point, I want tubers under the ground to grow, so you stop the fertilizer to encourage potato growth), and am now just waiting and wondering what is growing down underneath...???