Well, I donít grow any veggies, just annual and perennial flowers. My plants are usually in rather small containers (until transplanted outside) so itís pretty easy to tell when they need water by just how heavy or light the container feels. Sometimes however (with plants in slightly larger pots), I will use a moisture meter. The one I have is a Luster Leaf 1820 Rapitest; it was inexpensive and it really works great. If you have trouble judging when to water your tomato plants, a moisture meter might be something to consider.