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frost tolerance of mature onions

Posted by jeaninmt 3a (My Page) on
Sun, Sep 2, 12 at 17:06

Hello All,
This year I have the chance to leave the water off the onion patch in hopes of some natural drying down. Normally the tops don't dry down at all as we have to harvest before the ground starts freezing with the first heavy frosts in early September.

But I began wondering what the frost tolerance is of mature onion bulbs and have not been able to find out in my books or online searches yet. Any ideas from you guys ?

I have been trying every year to plant the starts more shallowly so the bulbs have more room to grow. But now I am thinking they are less frost tolerant that way, with the bulbs part way above the ground...

The water has been off of them for 2 weeks now and they aren't showing any sign of drying down. We have had 2 nights of 30 degrees and I put row cover over them to protect the bulbs.

Normally we just pull them in late August and hang small bundles over the gates in the barn for a month to finish the drying process.

Thanks for any ideas, Jean in Mt

Follow-Up Postings:

RE: frost tolerance of mature onions

Hi Jean,
I don't think they can take a hard freeze, just mild frosts. A hard freeze will rupture the cell walls and leave you with mushy outer layers.
It sounds like you really need to look into earlier maturing onions or try if possible to get them in earlier. Onions intended for storage should finish up while it's dry and warm. That said, I know your MT weather is not the easiest to garden in.
Perhaps a thick straw mulch might give you a few degrees to work with in addition to the row cover. Hopefully they will start to fall soon.

RE: frost tolerance of mature onions

How long do you leave the water off ? In the past I grew the onion sets, and they never died down. In the past 6 years or so I've grown my own from seed. That gets started in January and planted out in early May with mulch and row cover as we still get nights in the mid 20's.

The past 2 years I have tried several varieties, searching for the best storage onion and hopefully finding one that can produce seed in our short climate. Last year I grew Copra as the standard, even though its hybrid. Then Bronze d'Amposta, yellow of Parma and Brown Spanish. Brown Spanish and yellow of Parma stored all winter and are now racing to see who makes seed. One kind is in a neighbors garden miles away.

Can you suggest any great storage onions that have a shorter maturity ? The shortest I've seen are 90 - 100 days.
Thanks for any ideas, Jean in Mt

RE: frost tolerance of mature onions

It seems to me that you're doing everything right. If you seed in Jan. and don't transplant till May you must have some jumbo transplants!
For me, Copra or Cortland have been the earliest.
I usually don't have to cut water off till the tops just start to fall. I don't know how much you can speed along the maturity by water stress. Onions put on quite a bit of size from when they start to fall to when they get dug so it's good if the soil is not bone dry.

RE: frost tolerance of mature onions

Just for a follow-up on this... Just for kicks I left 10 onions out in the garden after pulling the rest. After another week or so, a couple fell over, bending at the neck. Somehow I've been thinking they would be dry when they fell over, but not so!!! I pulled 5 of them when low temps threatened and left 5. It got down to about 25 a few nights and the onions were fine. They were hilled up with dirt over the bulbs and bottom of the stems. Interesting !!!

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