Harvest your onions as soon as the ramrod-straight leaves start toppling over and turning brown.
Harvest your Onions
This is a sign that the plants are drawing all their goodness down into the bulb at the end of their season – your cue to dig up the lot for storing through winter.
Take your time over lifting and drying the crop, as the slower you do it, the better they’ll keep and the less likely they’ll be to develop rots in storage. The first thing you'll need is about a week without rain:
keep an eye on the forecast and try to time your harvest as dry weather is on the way. If the weather is unkind, you can always move them under cover into a greenhouse or sunny conservatory to dry instead.
Keep an eye on the forecast
Start by loosening the roots, just half digging up the bulbs with a border fork but leaving them in the ground: this breaks the contact with the soil and begins the drying process. Next day, dig them up and lay out on the soil or on racks in the greenhouse. Turn every few days to dry the skins evenly. After a couple of weeks, once stems are papery, trim away the roots and plant into strings.