I have 4 tomato plants, 2 in 5-gal buckets filled with potting mix and 2 in the ground with potting mix mixed with soil. The ones in the buckets are the oldest and have been producing good tomatoes. The other 2 haven't produced yet. All 4 plants looked great yesterday, but this afternoon the leaves on one of the ones in the buckets look all wilted and dry like it's dying and one of the ones in the ground is turning all yellow. HELP!!
Certified GKH Gardening Expert
It is likely heat stress that is causing the wilting and yellowing of your plants. Tomato plants need lots of water anyway, but with high heat (as has been the case in much of the country), they need even more, especially those planted in containers. I would up the watering to at least twice a day for the ones in buckets. This article will also help with watering requirements for tomatoes: https://www.gardeningknowhow.com/edible/vegetables/tomato/watering-tomato-plants.htm
For additional causes of wilt or yellowing, these articles may help: https://www.gardeningknowhow.com/edible/vegetables/tomato/wilting-tomato-plants.htm