An onion that is not harvested must be empty.

The autumn equinox does not collect onions, and the first frost is empty. "No onions are collected in the autumn equinox, and the first frost is empty" means that no onions are collected in the autumn equinox, and the first frost is air-cooled, and onions may be empty. Because after the autumnal equinox, the days get shorter and the nights get longer, and the temperature will get lower and lower. For green onions, the colder the weather, the less cold water they absorb, especially the roots of onions. After entering the autumnal equinox, it does not directly enter the winter, and the temperature at noon is still relatively high, so the water in the onion is still evaporating. If you don't pick green onions at this time, they may lose their edible value because they are hollow when you are in the first frost.