We live on the 4th floor of a unit bock and our cumquat tree flowered but produced very little fruit. Do they need fertilising by bees?. We have seen no bees at our height.
Pollinate your plant. Kumquat trees that are grown indoors may need to be hand-pollinated to trigger fruit production. It's easy to do. Just take a small, dry paintbrush and wiggle it around the center of each flower, moving from flower to flower. This carries the pollen from male to female flowers, just like bees do it.