Posted: 26/07/2017 at 16:16
The only thing I can suggest is that you are harvesting them too early. I usually wait until the roots have let go and the foliage has not just flipped over but dried off completely. I ensure once they are out of the ground that they are not rained on. I usually ripen them in the greenhouse and store them in plastic trays, but that is just a preference of mine.
The length of time an onion will store is also dependent on the variety. Remember farmers who grow for supermarkets have access to all sorts of growth retardants which they use to make sure the crop lasts well into next year.