Last year my tomatoes did pretty well at first but about mid season they seemed to expend all energy growing vines with little or no fruit. The vines were 0.75 inches in diameter and about 12 feet long. Can I prune them at some point to retard vine growth and produce fruit? If so, at what height should I cut the vines? Many thanks.
It sounds like the plants were getting too much Nitrogen. That's the first thing I think of when I hear my plants are doing great but they aren't blooming or setting fruit. Tomatoes don't need a lot of Nitrogen but they do need phosphorous, to induce flowering and fruit set.
You can always use a spray on liqued fertilizer and spray the foliage as well as the soil, there are also granular fertilizers that you put in a hose end sprayer and it mixes with water as it sprays. Phosphorus is the middle # of the 3. Nitrogen, phosphorous, potassium, I'd pick a fertilizer that has a high middle # and just follow the directions. Just don't spray during the heat of the day, it will burn the leaves. Can't be 100% sure thats the problem without soil samples but it sure seems like it.