Experts and BHG readers answer.
Watering Tomato plants
It's best to water early in the day, but when your plants are so stressed that they're wilting, water right away and don't wait until morning. A soaker hose is best, but you can also make a soaker system from a set of plastic buckets. Drill about a 1/8-inch hole in the bottom of each bucket. (I prefer to have the hole very low on a side of the bucket so it doesn't clog as easily.) Set one bucket next to each plant, and then fill the buckets with water. Water will trickle slowly from the holes and soak in deeply. If you have no weeper or soaker options, water with a wand and keep the nozzle close to the ground so that the foliage won't be wet overnight. (When you water earlier in the day, a sprinkler is far better than a watering wand.) It'd also be a good idea to mulch your tomato plants to maintain soil moisture.