Blossom End Rot!

I thought my tomato plants were doing so well, but it turns out they have a problem! Some of the tomatoes are getting something called "blossom end rot", which means the bottoms of the tomatoes are rotting. I was pretty disappointed when I discovered this. Not all the tomatoes have it yet. I'm still hoping to get some lovely fruits from these plants.

So what causes blossom end rot anyway? I did some research, and it looks like extreme heat can do it, and lack of fertilizer. I don't think I've been fertilizing properly, so I gave each plant some food. I hope that will solve the problem!