Onion seedlings in a coldframe?

wayne_county_man(WV_6b)January 15, 2011

Does anyone know if you transplant onion seedlings (4-6 week old) to a coldframe in late Feb. (4-5 weeks before recommend outdoor transplanting time)? I have started my onion seed today and thinking trying this. Any experience with onion seed transplants?

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Howdy Wayne: I grow my onions from seed which is planted into a 288 plug tray. In case you don't know, a 288 is a single sheet of plastic the same dimensions as a standard flat you'd see in a greenhouse for growing flowering annuals and veggie transplants. The difference is the plug tray has 288 cells in it and they are only about an inch deep. This method has worked very well now for 5 years or so and allows for growing many plants in a small space but you have to watch the water very closely, especially when the trays start going outside on warm Spring days since there isn't much growing media to hold water and they can dry out in a hurry. the plugs push easily with a drill bit tail end and the planting hole is easily made with your finger.

The biggest downside is the inability to hold full sized plants for too long if the weather turns to crap for a long time when it is time to plant; if it does, I cut back the tops about half way and cross my fingers for dry weather, hasn't caused me any problems yet.

Gotta go!

    Bookmark   January 15, 2011 at 3:22PM
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laceyvail(6A, WV)

Hello Wayne County Man. Monroe County, WV here. I start my onions in a flat the first of March, cut them back as needed to keep them at 3 inches, and transplant to the open garden in mid April when the seedlings have some size. Crowding onions in the flats doesn't present a problem. I get huge onions that I harvest in early August. Keep it simple and don't make a lot of extra work for yourself.

    Bookmark   January 16, 2011 at 6:09AM
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Do you grow them under lights?

    Bookmark   January 16, 2011 at 9:04AM
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Initially, yes, then it's off to either a window, the cold frame or the great outdoors, weather pending. If memory serves me correctly, Onions must have light in order to germinate.

    Bookmark   January 16, 2011 at 5:35PM
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I start several onions, shallots and leeks under lights in a really cold basement, with bottom heat until germinated. I make thick rows in plastic mushroom/produce trays. I start them by Feb or as soon as i can.
They are quite happy to move out of the way from starting the next round of coles, or warmer weather seed, by being in cold, southeastern windows. They fare as well as any bought bunches of starts, or better.In my strawbale cold frame, i liked to keep small onions to have fresh in the kitchen thru winter - but they didn't flourish with the light(like me, right now!!).

    Bookmark   January 16, 2011 at 6:33PM
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laceyvail(6A, WV)

I carry all my seedlings outside to the south side of the house as soon as they germinate--if the weather is above 40, and back inside at night. Not as much work as it sounds since I don't have a huge garden and it's a rolling operation. Onions the first of March, peppers a week or so later, cabbage and broccoli the week after that, tomatoes the end of March. It produces really terrific plants.

    Bookmark   January 17, 2011 at 6:05AM
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The question was about planting in a cold frame. The advice sought would probably be along the lines of..."it's ok as long as overnight lows stay above x degrees." Or, "growth will be better indoors until outdoor temperatures average x degrees in your location." Not... "I plant mine in March ;) lol," as if that means anything since temperatures in March vary by location.

    Bookmark   February 1, 2011 at 10:00PM
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As wgl58 said, planting in a cold frame varies depending upon region.

Cold frames are much like small green houses. Don't let it get too hot in there otherwise you'll cook the plants.

Not sure why you'd want to plant them in a cold frame, but each gardener has their own way.

Regarding onions needing light to germinate - I do not believe this is the case. I've germinated many onion seeds - all sowed about 1/4 inch deep in trays - and they come up well. Now celery - on the other hand - absolutely must have light to germinate! I learned that last year when less than 10% of my celery sprouted that I actually covered with soil. After I began putting the celery right on top of the soil and allowing water to be pulled up from the bottom, I've had well over 70 - 80% germination rates.

If you want to grow onions indoors, I used those trays with 72 cells in a tray that is about one foot wide by 2 feet long (maybe not that long). Each "plug" was about one inch square and maybe 1.5 - 2 inches deep. This year I just filled the trays with soil, planted the onions 3/4 to one inch apart, and in the past 13 days, 126 out of 200 have come up from year-old seed.

Now - about cutting the tops of the onions. I've seen people do it - I've seen people not do it. Last year I was one of those that did cut the onions to about 2-3 inches long. This year I'm going to see what happens when not cutting the onions and allowing them to grow.

Here is a link that might be useful: BsnTech Gardening Blog

    Bookmark   February 3, 2011 at 9:48PM
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BSNtech: the only reason I ever cut the tops is to make them easier to handle when transplanting them, the tops can get kinda tangled together in the flat if they get too long. One possible benefit could be that the trimmed tops don't flop down and touch the soil after transplanting, from a disease standpoint that is a good thing.

    Bookmark   February 5, 2011 at 3:26PM
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Good point.

Onions I planted back around December 19th are getting fairly tall and as you said - they are getting a bit tangled together. I'm also having to keep the lights a little higher because of this as well.

I think I'll succumb and cut the tops a bit because of these two issues.

A nice fellow here on the forums is sending me about 100 Varsity Onion seeds - seed that FedCo was already sold out of when I put my order in. Therefore, I should get those in a couple of days and will start them immediately. As long as I can find room in the garden, I'm quite interested to see how they compare to Copra Onion in size and storage longevity.

I have alloted room for about 110 onions - and right now, I have about 146 currently living (although I bet I'll lose 20+ of those since some of them don't appear to be growing). Add that to the 100 or so Varsity onions - I'll need another 4 x 8 growing area to put all of these.

Already dug up my front yard enough that I do not want to make another bed.

    Bookmark   February 6, 2011 at 11:28AM
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franktank232(z5 WI)


I've got about 150 Cortland F1 seedlings going right now under lights. I plan on cutting mine back some. The problem i had last year was that i started them in 50 cell trays... By the time I planted them out the roots were just a huge mess. I think this year i'll try to get them in the ground ASAP. I may have waited too long last year. I plan on starting more onion seed soon. I just shove onions where ever I can find room. They need very little space/soil.

    Bookmark   February 6, 2011 at 12:14PM
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I planted my onion seeds inside and kept warm until they germinated. Onions are fairly hardy plants so they can tolerate quite low temperatures. I put mine out in the cold greenhouse as soon as they are about 2 cm. tall. When they are big enough to be handled they will be put into individual pots or cell trays. I usually add a little mychorrhizal fungi when transplanting.

Here is a link that might be useful: Onion seed planted

    Bookmark   February 6, 2011 at 2:37PM
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Thanks for all the info everyone - I have never grown onions from seed. Here in the part of WV I live in our average last frost is late April/ early May. I am thinking I wil go over board with seeding to allow myself options. One - I have already got seedlings coming up ( three weeks and three inches tall) so I think I will transfer them to a coldframe (6 haybails square with 6 inches of fresh manure) in their pots and see how they manage for the next few weeks. Two - I think I will sow more seed in early March and once germinated I will try them under a plastic hoop tunnel to prevent getting burned. Will see what happens I guess. That's why I love this sport and I couldn't tell you who is winning the superbowl!!!

    Bookmark   February 6, 2011 at 9:34PM
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