I have tomatoes and peppers growing in a half whiskey barrel and when it is sunny they seem to wilt badly during the day. When I stick my water meter about 4" down in the soil it shows pretty wet. Do I need to water them every day to keep them from wilting so much? It is a little disconcerting to see them so limp.

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Gary in Soutn Carolina

With tomatoes, you can bury the stems in compost and they will put out more roots on that part of the stem. Then mulch the compost.
When you water, you need to do it less often and more deeply to encourage the roots to go deep for the moisture. Your soil may not be well enough drained too, which would account for a shallow root system.
Try mulching with a coir mulch or similar to prevent the soil from drying out near the surface on your peppers. It's possible they are wilting because the soil itself heats up too much, so try shading the actual barrel, maybe with other potted plants or similar, to keep the soil cool. They like the heat but their roots don't.
Also, maybe look at watering them late morning if possible, so they are getting moisture just before the heat of the day hits them.

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The secret is the soil.