Onions do not develop

tulsabrian(7)December 22, 2008

My aunt asked if I would run this by you guys. She has put out onion sets repeatedly but although the tops grow, the "bulb" never gets any bigger than what it was when planted. She plants on the south side of her house and composts regularly (she lives in Minnesota) and has an automatic watering system so moisture shouldn't be an issue. I've never had a problem getting onions to develop so I'm hoping someone out there has some ideas.

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Okiedawn OK Zone 7


I've never had trouble getting onions to bulb up either, unless I deliberately planted a long-daylength type to see how it would grow here--and I knew it was an experiment and didn't expect much if any bulbing. But, I get asked this question a lot, so I have a few ideas, but you'll have to run through the list below with her and try to figure out which one it might be:

1) Does she use the little dried sets that look like bulbs.....the kind you buy in cellophane bags punched with air holes? If so, that's probably the problem. It seems to me that the dry sets more often produce green onions (similar to the scallions you buy in the grocery store) and not bulbing onions. I don't know why, but it seems to happen a lot.

2) If she buys bundled onion transplants like we do here, is she buying them locally so she is sure to get a long-daylength onion? In her climate, she can grow the long-daylength onions, and maybe the intermediate or neutral daylength onions, but not the short day-length onions.

3) Is she planting at the recommended time for onion-planting in her state? Planting at the proper time for your geographic location is the key to getting your onions to bulb up. Remember that onions bulb in relation to day length, so onions that are planted too late are too immature to bulb up when the daylength hits the right point. If she plants too early and the young transplants are exposed to temperatures below 45 degrees for a prolonged period of time, they are more likely to bolt and go to seed instead of bulbing up, or they just sit there and don't grow well and don't form large bulbs.

4) Is she setting out transplants that are the right size? The best transplants will be smaller in diameter than a No. 2 pencil (about 1/4"). If she plants transplants that are larger than that, they are more likely to bolt or to fail to bulb up. This is because onion transplants are held in cold storage which can make them go dormant. Going dormant while less than 1/4" is not a problem and does not affect future growth or bulbing, but going dormant while larger than 1/4" can be a problem and can inhibit bulbing and/or cause bolting.

5) With liberal amounts of compost, fertility should not be an issue. Does she get big healthy green tops? If so, they are getting enough nitrogen and nitrogen is key to having healthy onions. Did you know that for each leaf you have, you'll usually have one "layer" or "ring" of onion? So, for the biggest onions, you want to water well and raise the plants in nitrogen-rich soil so you'll have lots of green topgrowth at the initiation of bulbing; and, if you do, you'll have big onions. I prefer to use manure as a natural source of nitrogen in my onion bed.

6) I know nothing about the soils in Minnesota, so you might ask her if she has ever tested the pH of her soil. Onions grow best in soil with a pH above 6.0. If her soil pH is below 6.0, she can raise the pH by adding agricultural lime to her soil.

7. Does she irrigate at the right time? A lot of people only water their onions a lot early on in the growing process--while the plants are forming leaves and then stop watering as much later on. In reality, research has shown that onions benefit the most from being well-watered during the period of time from the initiation of the bulbing process until the time that you begin to see the standard signs of maturing--a slowing down in the growth of the bulb and a softening of the neck. When you see the neck softening, that's the time to begin withholding water so the onions can dry out a little which will help them to cure more quickly after they are harvested.

8) It also is possible she is planting her transplants too deeply, and that can lead to a lack of bulb formation. Onions must be planted very, very shallowly. If they are planted too deeply, they may not bulb up.

Finally, "the" onion experts are the folks at Dixondale Farms. They have great FAQs and an onion growing guide on their website, which I have linked below. If there's anything that anyone needs to know about growing onions, you can find it at this website.


Here is a link that might be useful: Dixondale Farms Onion Info

    Bookmark   December 22, 2008 at 7:53PM
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