What is causing the bottom of my tomatoes to turn black?

https://bonnieplants.com/library/conquer-blossom-end-rot/

Thats it too much water

garden soil that is infected with a tomato blite can cause the bottoms of tomatoes to turn black. So can wet soil if the tomato is actually touching the dirt. If you have blite this year, you won't beable to grow tomatoes there next year because the disease stays in the ground, even over a cold winter. It did in our garden.

when I was growing my tomatoes the had black spots on them too...I called mom who had a green thumb for everything...she told me my soil didn't have enough calcium in it and too take my eggs shells and crumble them up and put them in my soil and it worked....from then on I would save all my egg shells and add them to the soil in the spring before I would plant me tomatoes and never had black spots again....

Blossom end rot is from not enough calcium in the soil.You can do what Lady52Dragon suggested,you can buy bone meal at a garden center and sprinkle around the plants or you can crush and desolve aa couple of Tums to water in and I've heard people say you can crush a regular aspirin and water that in.Hope one of these helps.

It is not blight -- that makes the leaves curl up and die and is in the soil. If the fruit is turning black, you have blossom end rot as mentioned above. It is technically related to not enough calcium but NOT the calcium level in the soil. It is because the plant is unable to take in the calcium fast enough to feed the fruit. This could be because the plant has grown too quickly but usually is caused by inconsistent water while the fruit was set (i.e. you let the plant dry out too much between waterings so it did not take in the calcium). The good news is this only affects that fruit . . . new tomatoes will not be affected as long as you water properly.