Q.What are these black marks developing on my tomatoes and how do I deal with them?
These black marks have started to develop on a few of my immature tomatoes – I cut them off to prevent it spreading. Pictures attached. Please help.
Certified GKH Gardening Expert
That would be blossom end rot! This is caused by lacking in Calcium (and Magnesium, since they are taken up together, but many people don't know this!) There is a very simple way to fix this problem. All you need is DOLOMITIC LIME. That's it. It supplies, both, Magnesium and Calcium at the same time. There are many ways to combat this, but this is the easiest (and least expensive) way to go about this.
These articles will help: https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-blossom-rot.htm
Can blossom end rot also appear from the side of the fruit? In all the example pictures I've seen online the blossom end rot develops in a uniform way around the withered blossom - on my fruit it's appearing on the sides. I just wanted to be 100 percent sure it isn't another condition. I will still treat it for blossom end rot in the meantime - I can't see it doing damage if it's not the case! I think you're probably though right by the way - judging by the artcile that you linked to me (we've experienced extreme heat followed by heavy rainfall plus I have many plants in a large tub meaning they've all received some nitrogen at varying times in their development etc).