Onion germination

Any time I grow onions from seed, some percentage appear to generate a radicle that points up and dries out. The seed then dies. Why do they do this?

I dunno i always start a whole flat with a whole pack of seeds and do the 1 year method for hardening / moving them along fast. Its my understanding that onions are a numbers game

Hi, can you explain what the one year method is? Or whatever you do to succeed with onions from seed until harvest?

Start a bunch of them closely in a flat tray about 12 weeks before last avg frost, Give them good light and make sure to keep them not over but evenly watered during there grasslike phase start bringing them outside and hardening them off and they swell up make mini bulbs and have multiple leaves, then you dump them out or wash the soil out of them and you have a bunch of onion sets to plant . I believe i got this method from someone off here a while ago?

I live in a semi arid environment and root rot is not an issue and they do not need much supplemental irrigation so maybe yours need to be in raised beds or less water? We average 12-16" rain and have dry spots in the summer but they do pretty well on there own and thrive with supplemental feeding. They are pretty easy in my climate.

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Mine aren’t doing too badly. I just use these pots and aim for maybe 25 plants per pot.

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At least you showed some restraint in sowing. I’ll be giving about 75% of these away.
Alisa Craig Exhibition, Cabernet F1, Red of Florence, Yellow of Parma and Walla Walla.


Yeah im with Zendog! BG that looks like a way more reasonable way to plant them than the way i go about it

Thanks. My problem is they tend to bulb too early when I try starting them from seed, before I can take them outside. And they never mature into anything larger than a garlic.

Also, am I supposed to keep cutting back the green part of the seedling? I read that somewhere.

Hrmm too big never seemed to be a problem, mine usually take off right after re transplanting. They only get maybe the size of a pencil at most for me to half that in size. Do you give them a week or two of cold evenings before transplanting? How many varieties have you tried? I started with a lot and have ended up with 4 or so that work great for me. (walla wallas, Cippolinis, shallots and tokyo scallions)
I have never cut them but i do get rid of the seeds on there tops as they bother me, but maybe someone else would have a better idea about cutting tops. They need good light is my main understanding?

I haven’t had that issue, although I do make sure to keep the light timer at no more than 11h25m for intermediate. I don’t grow short days. I grow intermediate and long. I am at 39°N.

I have had them at about 2/3” at transplanting (not bulbing) with no issues, but typically they’re more like pencil-sized.

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Honestly, my main concern is rot.

Last year, about 75% of my onions were lost to what I believe is center rot. A couple leaves would turn to slime before harvest, and while the bulb looked ok externally, one or two rings inside would be soft and brown. Many were ok if you cut deep enough into the bulb, but those ones didn’t keep long.

I swear i use to grow onions better then i do lately…i pre soak mine and then put them in flats on heat…but yeah i get a lot of duds… put multiple seeds per cell and then thin…

It is funny how some things do better when you have no idea what you’re doing.


I start mine like RichardRT and just use them like the onion secklings you can buy. We are in a cold zone so mine have to be started early and when they get tall I just keep trimming the tops down to 3 or 4 inches. I grow under lights but they still seem to flop so I just take the scissors and trim. The onions, in the greenhouses up here in the spring, are all cut down to 3 inches in size so that is what I went with.

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It’s funny. I always get some noticeable percentage of what appears to be damping off, they start to sprout, then shrivel up.

I’ve been doing this for several years, and it seems to happen no matter how moist or dry I keep them, no matter how warm or cold. I’ve kept them on the verge of almost dry, I have put plastic over them to keep them as moist as possible, and I’ve tried different media. It doesn’t really seem to matter.

The only thing I will say was the increased moisture of covering in plastic did increase the damping off a little, but I’m still getting quite a bit even with the fan on them, and a relatively dry media this year.


Interesting. I never really see any damping off on onions (and very little on other seedlings), but my relative humidity is usually around 40%. Also, they are on mesh racks that might be helping the air flow as the warmth from the lights probably keeps the air rising through the shelves. Do you keep a fan on them?

The only one’s that I see fail to thrive are the ones where the seed head gets caught in the soil too long and the root end is pulled up out of the soil. If I catch it early enough, I use a pair of tweezers to grab the end of the roots and push the tweezers down into the soil dragging the root end back under… mostly works if I don’t pull the roots off by mistake.

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My humidity is 28% right now. Maybe it’s TOO dry?

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That does seem quite dry. I would be surprised if you were getting much damping off at that humidity unless you were keeping the soil really wet. Could it just be seedlings that don’t have good roots and they’re actually drying out? I guess the good thing is onion seed is cheap so it is easy to just overseed to get what you need.

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It’s tough. My grow room is in the corner of the basement, so I can’t really humidify it, because it’s not closed in at all. Without a fan, it gets way too hot under the lights, which of course makes the relative humidity lower and makes them dry out. With a fan, temps are cooler but the wind itself dries them out.