My wife found a great trick in a book that is perfect for not only
making sure the water goes right where it needs to, but also
regulating exactly how much water the plant gets. We take empty 2
liter bottles and cut the bottom 1 inch off of the bottom with a box
cutter. We then bury them 1/2 way underground right up against the
tomato plant. Voila. You water the tomato plant by filling the bottle
with a hose. Easy peasy. You dont have to worry about run-off or over-
watering. The water enters the ground right where the roots need it,
plus the bottle itself is a perfect water-volume measuring tool.

But it should be said, mulching is a must.