Answer: Watering depends on the weather and on the type of soil and on the plants you are trying to grow. In dry weather, windy weather or hot weather the soil will dry faster. Sandy soil will drain quickly compared to clay soil. Clay soil will dry out slowly, but once it is dry it requires a lot of water to re-wet it. The water must be applied very slowly so it soaks down into the soil. And a garden on a hill will be naturally drier due to runoff, with the top of the hill being driest and the base of the hill damper.
Your goal in watering is to supplement rain as needed to suit your plants. Tomatoes need soil that is evenly moist. This means damp like a wrung out sponge, not sopping wet/saturated and not dried out.
The best way to know if you need to water is to check the soil by digging down and inch or so with your finger. If it is still damp you do not need to water yet. When you do water, apply it slowly and thoroughly so it soaks down to the deeper roots. Avoid wetting the foliage when you water, apply it directly to the soil. After watering, wait a few hours (overnight if you have clay soil) and then dig down to see how far the water actually penentrated; sometimes it is surprising. It is better to encourage deep roots by watering deeply less often than to water lightly every day. Using an organic mulch several inches thick will help keep the soil moister and will also help feed the soil slowly over time as it breaks down.
Also, you can improve your soil by adding organic matter. This helps sandy soil hold moisture longer and also helps open clay soil so it does not compact so hard.
As far as your tomatoes dieing, this could be due to a disease or pest problem or possibly related to over or underwatering. You might want to consult with your local county extension for a more specific diagnosis. Usually it is a good idea to quickly remove affected foliage and tomato plant debris from the garden and dispose of it in the trash. This will help limit reinfection if it is a pest or disease problem.
I hope this helps!
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