Your tomato plants have been pollinated, and you begin to see little tomatoes forming. As the fruit grows larger, the stem supporting them grows thicker to support their weight. However, if your tomatoes are of a larger variety, despite the significantly thicker stem, they might need some extra support.
I have noticed, with my plants, that the smaller tomatoes seem a-ok, but the bigger ones are starting to hang down dangerously. One branch, in particular, was starting to crease and bend a bit in a way that spelt disaster. So, apparently, tomatoes might need support.
I ran through a bunch of ideas, and what seemed the best was to create a sort of hammock (or a sling, perhaps), to support the entire bunch of tomatoes. This hammock should be tied to a support above, such as the trellis or rope supporting the plant itself. If you haven’t provided a support for the plant, you should probably start thinking about it.
Of course, like with everything, this will create some problems. Less sunlight, less air circulation… But it’s worth it, I think, especially since not all plants will require support. Besides, late fruit is better than no fruit at all.
The image on top is of a makeshift hammock I made with a long piece of fabric. It is a soft, breathable fabric folded twice along its width, and tied onto a tap above the plant. The image immediately above is a shot of the hammock from below. Image copyrights belong to me.