Question: I have a bumper crop of Walla Walla and red onions this year. A lot of them are 4 inches in diameter. When should they be harvested? How should they be stored to make them last longer without spoiling?
Answer: Onions can be harvested as needed for fresh use. Onions keep best when fully mature with several tough skins over the bulbs. When they reach maturity, the green stalks naturally bend over. Some gardeners bend the stalks over to hasten maturity. This is often done by “stepping on” the stalks. Give the bulbs a week or two after the stalks are bent for an additional layer or two of skin to develop.
Onions store best under cool, dry conditions. Unfortunately, Walla Walla is not a good storage onion. It would be best to use them first. I usually just put the bulbs in the refrigerator vegetable drawer. The garage is a good place for longer storage. Put bulbs in a loose weave sack such as an onion sack. You can often pick onion sacks up from a grocery store, just like you do fruit boxes. Pantyhose also work well. Ideal temperature is between 35 and 50 degrees F. Don’t let them freeze.
Question: I also have a good crop of red potatoes this year. When should they be harvested? How should they be stored?
Answer: Potatoes are ideally harvested about a week or two after an early frost kills the tops. Just like onions, they need a little time to develop a thicker, tougher skin. It takes a lot of time for commercial growers to harvest their total acreage, so they often kill the tops by spraying with sulfuric acid or other chemicals. They need to get started in early September so they get all the tubers out of the ground before the ground freezes. Gardeners typically wait for the frost, since it only takes a day or two to get them out of the ground.
Potatoes like temperatures between 35 and 50 degrees, but a little higher humidity than onions. They can be stored in clear plastic produce bags with holes to increase humidity. Temperatures below 40 degrees cause some of the starch in the tubers to turn into sugar. This makes them turn brown when fried or taste sweet if cooked immediately after removing from cold storage. However, if they are moved to slightly warmer temperature (45-50) for a week or so, they lose their sweetness. I have stored potatoes successfully in my garage for up to 5 months. However, I sort through them about once a month to remove any spoiling potatoes. A leaflet on home storage of potatoes is available from the University of Idaho. I found it by googling “potato storage”.
After about 3 months, commercial growers will often gas potatoes with sprout inhibitor. I do not recommend trying that in a home situation. If potatoes begin to sprout, you can remove sprouts by hand to make them store longer.
Other vegetables which will store for long periods include carrots, parsnips, turnips, beets, cabbage and winter squash. All except winter squash store at 35 to 50 degrees. Squash likes a little warmer temperature (45-55 degrees). All will be damaged if temperature goes below freezing.