Harvesting, curing and storing onions from your garden
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Onions are a staple in our diet, and pretty easy to grow and store. As we near the end of our growing season I would like to discuss when to harvest and how to cure and store onion bulbs.
Onions tell us when they are ready to harvest—the neck weakens and the leaves tip over. This indicates the onion has stopped growing. The necks can be forced over, but this will not necessarily stop the growth, making them difficult to cure properly. Different cultivars will mature at different times. When harvesting large patches of onions, the rule of thumb is that when about half of the tops have tipped naturally the rest are close enough to maturity that they will cure properly.
Harvest when the plants and weather are dry. Don’t irrigate for about a week before harvest.
When the tops have tipped it’s best to use a garden fork to loosen the soil under the bulbs, then gently lift them—avoid pulling off the tops or bruising the bulbs. It’s that simple.
The purpose of curing onions is to reduce the chance of spoilage and prepare the onion for long-term storage. Dry, outer scales will make a seal around the bulb.
Commercial growers harvest and top the onions, then take them to a controlled atmosphere building to quickly dry and reduce the temperature. Home gardeners may need to be a little more creative.
Once the bulbs are lifted it’s best to get them out of the sun and into a shed or garage, with good air circulation, so the outer scales can dry and the necks seal. Curing temperatures are best between 70 – 85⁰F. Relative humidity should be around 70%, usually not a problem in eastern Idaho.
It may take 2 – 4 weeks to cure the onions. They are cured when the neck membranes don’t slip. Rub the neck between you thumb and forefinger. You’ll be able to tell if it slips or is dry. This reduces the chance of disease organisms entering the bulb through the neck.
When there is no slip, cut off the dry leaves an inch or two above the natural bend of the neck. You will lose about 8% of the weight of the onion in the curing process.
Do not remove the onionskin membrane until you are ready to use the onion. The length of storage depends a great deal on the cultivar. More pungent onions tend to store longer, up to nine months. The Spanish yellow, and Walla Walla sweet onions will usually only store for about 4- 6 weeks. Onions should be stored in a breathable container—mesh bag, nylon stockings, wicker basket. They will store best when temperatures are consistently between 32 – 35⁰F, and humidity is around 70%. Onions stored over 40⁰F will break dormancy sooner.
It is important to bring them down to this temperature slowly, over a couple of weeks. Inspect the bulbs before putting into storage and promptly use any that have been damaged or have loose necks, which allows disease organisms to enter the bulb. Of course, you can always chop and dehydrate or freeze the onions as well.