You may have noticed some of your citrus don't have the female ( stigma ) part in the flowers which means it's impossible for them to set fruit. This seems to be more common in certain types of citrus and is probably more common in younger plants. I'm not sure if this is simply poor genetics, immaturity of the plant, or possibly a mechanism to encourage cross pollination rather than self fertilisation or to prevent a plant that is too young from setting too many fruits.
