Lonely Tomato

I planted two tomato plants at the side of my house in the landscaping in May. Both plants appear to be growing quite nicely with lots of blooms. I monitor them quite frequently to make sure the family dog has not nibbled the branches because she loves to trim my landscaping. Seems all is well. I became quite excited when a tiny green bud appeared and it has grown to the size of a tennis ball and is nice and green. But....it's the only one! I keep waiting for it to turn red but there is no hint of it turning. There are lots of other blooms but nothing is becoming of them. Unforturnately, the soil is extremely poor on the property, mostly clay. It may be that the plants' roots have hit the clay soil and can't seem to grow any more. Who knows. I love green tomatoes but I thought I'd let the first one turn red. I can't wait for the lucious taste of something that is not HOT HOUSE!