Answer: I've never been a fan of moisture meters because they can give false readings. To keep your tomato plant well watered, build a basin or water well directly beneath it and fill the basin, allow it to drain, then fill it a second time. This allows the water to trickle down and wet the entire rootmass. Deep watering is preferable over more frequent, light watering. You want moisture to go deep to all the roots of the plant. This watering method helps keep water off the leaves; tomatoes are susceptible to plant disease that grows in wet, humid conditions. How often you need to water depends upon your soil type and the weather, but twice a week deep soakings should do it. Try watering as described above, then waiting 2-3 days and digging down near the roots. If the soil is still moist, you won't need to water for a few more days; if it is dry, it's time to water. Consistent soil moisture, as opposed to feast and famine, will keep your tomato plants producing healthy fruits all summer long.
Leaf curl may very well be normal for your plants and is not always an indication of a need for water. Water as above and your plants should be healthy and happy.
Hope you have a bountiful harvest!
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