I have a healthy-looking balcony tomato (a Polfast), which has produced at least 25 flowers so far. Two have gone on to become tomatoes - still green, but getting larger every day. The other flowers just shrivel and drop off. I googled around and learned that this is caused by wild temperature swings, which we've definitely had in Manhattan this summer - not much I can do about that. But is there anything I can do to help my tomato set fruit? It's very disheartening to see all those sad little stumps. I don't feed the plant anything but eggshells and water - maybe that's the problem.