QUESTION: – What happens if you leave onions in the ground? – Tamara W.
ANSWER: – If you forget to harvest your onions and leave them in the ground to overwinter, one of three things will likely happen to them. Some will rot, some will start to grow again in the spring only to bloom quickly, and some will start to separate into garlic-like sets, which can be planted and used to grow scallions in the spring. Overwintered onion sets, while great for growing scallions, should be avoided when you are trying to grow full onion bulbs, as these sets are quick to flower. When onions flower, the plant focuses all of its energy on producing the flower, instead of focusing its energy on strengthening its root system and creating bulbs.
If you want to grow full sized onion bulbs, you will want to start with seedlings, and when thinning, allow each plant plenty of room to develop bulbs without encroaching on its neighbor’s space. If you like growing scallions, leaving a few onions in the ground at the end of each growing season is probably a good call. If not, you will want to harvest your onions when the bulbs have stopped growing.
For spring planted onions, you can start harvesting them when the leaves start to become discolored and the onion tops start to fall over. Some onion growers say to wait until around half of your onion tops have fallen over, then harvest the whole crop of bulbs. Others suggest harvesting onions on a more case-by-case basis, feeling for a soft spot in the onion tops. Finding the soft spot in your onion tops is an easy way to know for sure that the bulbs have stopped developing.
Generally, leaving onions in the ground past their harvesting date is frowned upon, seeing as the onion sets the left in the ground onions produce are only suitable for growing scallions and may be quick to flower when regrown in the springtime. However, this does not mean that you have to harvest all of your onions when half of the tops have flopped. Leaving some onions in the ground for an extra couple of weeks could result in larger bulbs, as some onions are slower to develop than others. Depending on the weather in your area, you might be wise to keep your onions in the ground a little longer than suggested.
Some onion gardeners suggest waiting until 80 to 90 percent of your onion tops have fallen over, then wait an additional ten days to allow the bulbs to fully develop before harvesting. Another great tip for onion harvesting is to wait until the soil has had a chance to dry out between rains before attempting to harvest your bulbs. Waiting for the soil to dry out will make harvesting your onions much easier, and it also allows time for the tops to dry out before curing and storing, which will help you preserve your onions for longer.
For the best possible information about growing onions in your area, contact other onion farmers in your neck of the woods and ask them when they generally look to start harvesting their onions, and what their experiences have been leaving onions in the ground for late harvesting.
If you choose to leave some of your end of season onions in the ground so that you can grow scallions from the sets in the upcoming spring season, just leave some onions in the ground and dig them up as soon as the ground starts to thaw out in the early spring. The onion sets you are looking for will have multiplied and begun to split apart, similar to the way garlic cloves separate. You will want to dig these sets up, separate them by hand and plant them in the spring about five weeks before the last frost date in your area.