Southern Ontario, Canada. It has been crazy hot and humid - 33C plus humidity.
Do we need more water? Less? This is happening to about 1/3 of the tomatoes and they are not resting on the ground.
Edit: thanks everyone. She's going to start with a bit of lime and some more attention to how much she's watering.
She may even create a lemmy account now that she's seen how many helpful fellow gardeners around here, so win-win!
Thanks again
Blossom end rot.
Most commonly this is due to insufficient levels of calcium, which can be caused by too little available calcium in the soil, pH of the soil being out of range, or too much of other competing ions on the soil, amongst other issues.
Most often, this can be fixed with the addition of a little lime (i.e. calcium powder lime, not the fruit) added to the soil. Will take about 2 - 3 weeks to resolve if that's the issue.