The good news it’s not that scientific or complex either. By just keeping an close eye on your plants when growing onions, and knowing which key signs to look for, you can reap your homegrown bounty with confidence. As a guide, you can usually harvest around 100 to 120 days after the date when you planted onions. This can vary due to specific varieties, ground and weather conditions but is a useful marker for watching for the tell-tale signs such as yellowing leaves and when the erect foliage suddenly falls over.
When to harvest onions
Kelly Funk, president of Park Seeds (opens in new tab) says, ‘If you want crisp, tender green onions, harvest the bulbs just after the swelling begins. For mature bulbs, wait until the tops fall over after the growing season. Then dig up the bulbs, cure for three weeks, and store onions in a cool, dry place.’
When are fall-planted sets ready to harvest?
According to the RHS (opens in new tab), ‘Autumn-planted sets are ready to harvest by early to mid-summer.’ Avid veg growers Jim and Mary from Old World Garden Farms (opens in new tab) also comment: ‘As spring rolls around, your onions will come back to life. They can be harvested at any point as smaller onions or allowed to grow to full size for a mid to late summer harvest.’
How to tell when spring-planted onion sets are ready
‘Onions should be harvested in August and September,’ say the Southern States Cooperative (opens in new tab). ‘When your onion bulbs are ready for harvesting the leaves at the top will bend over. If they don’t, bend them over yourself and leave them in the ground for another two weeks. When harvesting lift the bulbs gently with a garden fork and spread them out to dry in the sun for two to four weeks. Turn them frequently, so they dry evenly.’
Do different colored onions mature at different times?
In a word yes. Scallions or green onions are usually ready to pick in as little as three weeks or once their fleshy green top growth reaches around 8 inches in height. Red and white onions grown for their bulbs will obviously take longer to mature. If grown from seed both red and white onions will take 100 to 120 days. If you planted sets expect mature bulbs to be at their best in 60 to 80 days.
Should I pick my onions before they flower?
As soon as you spot a flower spike emerging from a growing onion snip it off. This will prevent the plant from setting seed and hopefully stop from the bulb from splitting. Either way it is best to lift and use these plants relatively quickly, as they don’t tend to store well.
Can you leave mature onions in the ground over winter?
If you delay harvesting mature onions and leave them in the ground during the coldest months, they will begin to multiply. In the same way as a garlic forms individual cloves, an onion will send out tiny bulbettes. These can be separated and replanted as sets in spring.
