The borage plants in poly2 are starting to set seed so this is about how to tell when the seed is ready to collect and a way of doing it.
After pollination, the petals drop off and the sepals open out revealing the (normally four) seeds within. They start off white and firmly attached but as they ripen they turn black and drop off, individually not all at once. This is the time to collect the ripe seeds.
An easy way is to put a tray (or the lid of a box) underneath the ripening parts of the plant so the seeds have something to drop on to for collection. We also put something underneath and tap the plant to encourage the seeds to drop off. They are usually pretty dry and can be collected in a container. It is important to know what sort of seeds they are, especially as we grow both blue and white borage. In the box in this image we have added a blue borage flower to show which variety it is, but a seed label or bit of paper work just as well. Meanwhile, the bees are busy pollinating the newer flowers.