Mary's Veggie Garden

February 17, 2014

Onions in Storage: Copra vs Cabernet

Filed under: Onions,Vegetables — marysveggiegarden @ 3:41 pm

I garden with the goal of supplying most of our vegetables year round. For many vegetables, year round eating means storing the harvest for extended periods, half a year or more. Like gardening, storage is both a science and an art.  A little research will reveal the ideal conditions for growing or storage. The art comes from achieving something approximating those conditions at home.

2/17/14 top Prisma shallots, left Cabernet, right Copra

2/17/14 top Prisma shallots, left Cabernet onions, right Copra onions from my 2013 harvest

Last summer I grew two onion varieties. Cabernet matures in 100 days and produces “medium-large, globe shaped onions with deep red color….4-6 months storage.” (Johnnys). Copra is a medium-sized, yellow storage onion maturing in 107 days (Pinetree). I also grew a few red shallots called Prisma.

On July 29 I harvested 28 pounds of Cabernet onions, 107 onions weighing a bit more than a quarter pound each. On August 8 I harvested 23 pounds of Copra onions, 130 onions weighing .18 pounds each. All onions were grown from seed planted indoors 3/4/13 and transplanted into my garden 4/22. The days to maturity and the size of the onions were both as I expected based on the catalog descriptions.

After harvest but before storing onions must be dried. I laid mine on wire shelves placed in protected areas of the patio. After the tops were thoroughly dry, I snipped off the dried foliage and brushed off dirt and loose skin.

The next step is probably the most important. I sniffed each onion before bagging them in large mesh bags. I set aside any onion with even a hint of an onion-y smell. This pile went into a bag labeled ‘Use First’. It contained a handful of Cabernets and maybe 20-25% of the Copras. I did this to avoid last year’s disaster, when about a quarter of my Copra onions rotted in storage. (I’ve grown Copra for several years and usually they store extremely well.)

Ideal onion storage conditions are 32 °F and 65-70% humidity.

I hung the bagged onions from the basement floor joists where conditions were far from ideal – about 75°F and 50% humidity (controlled by a dehumidifier.) This is OK for a while as onions have a natural period of dormancy. The dormancy period is unique for each variety.

After 5.5 months of storage Cabernet onions show signs of sprouting.

After 5.5 months of storage Cabernet onions show signs of sprouting.

My basement is not heated so the temperature drops gradually with the outside temperature. By early December the basement temperature was in the low 60s when I noticed some of the Cabernet onions were starting to look green in the center, like they would be growing shoots soon. To lower their storage temperature, I put the bags into covered 5-gallon plastic buckets in my root cellar. With the increased humidity the Cabernets, but not the Copras or Prisma shallots, immediately put out roots. I guess the humidity was too high for Cabernet.

In the high humidity of a bucket, Cabernet onions grew roots.

In the high humidity of a lidded bucket, Cabernet onions grew roots.

Currently all the ‘root cellar’ crops are in the coldest part of the basement, where the temperature is  around 42°F. I brought them inside from the root cellar in early January when the temperatures started staying below freezing 24 hours a day. (I do not have a true root cellar.)

I just examined all the stored onions. Most of the Cabernets have roots but so far only 4 have grown a shoot. The Copras look good, no roots, no shoots, and only two looked soft. I discarded 2 of the shallots and the rest are fine.

The Copras and Cabernets are storing as well as described by the catalogs.  Even in poor storage conditions Cabernet did not break dormancy for 4 months and I think that time could be extended to 6 months by moving them to a colder area by mid-November.  Copra will start sprouting in mid-February if left hanging from the basement ceiling, but in a colder area their storage life is longer. I didn’t know what to expect from the shallots, but they have surprised me by keeping so well.

There are 60 Copra, 25 Cabernet, and 27 shallots remaining. We’ve used 2/3 the crop in 5.5 months so it will take about 3 months to use the remainder. I cannot store ‘fresh’, raw onions beyond March, as they will start to grow when the temperature gets warmer.  So it looks like I should chop and freeze the Copra’s before it gets warm. That should take us to ‘green onion’ time in the garden.

And this year I should transplant 10 fewer plants of each variety. I don’t enjoy cutting onions for the freezer and they really stink up the freezer.


  1. After freezing onions one year I vowed never to do it again. Everything in the freezer smelled of onions which is fine for the meats, but not so good for the zucchini bread.

    Comment by daphnegould — February 17, 2014 @ 3:49 pm | Reply

  2. You continue to amaze me with your record keeping, as I said many time, I keep trying and one of these days I will surprise you.

    Comment by Norma Chang — February 17, 2014 @ 6:27 pm | Reply

    • Onions are easy because all the counting and weighing is done at one time, when they get bagged up for storage.

      Comment by marysveggiegarden — February 17, 2014 @ 6:36 pm | Reply

  3. Fascinating! So far I’ve only stored garlic and shallots.

    Comment by Lisa and Robb — February 18, 2014 @ 3:20 am | Reply

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