I've been growing 1015 sweet onions (short day) for many years. In the past, I hadn't done any fertilization, and gotten decent sized (~3/4 lb) bulbs. This year, I salted the soil every three weeks with N fertilizer (ammonium sulfate). Kaboom! Every one of my onions is nearly a pound. Now, my soil is already rich in P and K, so I don't bother to amend with those. But N is highly leachable, and sort of comes and goes.

It is true that growing from seeds (or transplants produced by seeding) produces larger onions than growing from sets, which are tiny dried bulbs from the previous season. Allegedly onions grown from sets are also more likely to be malformed. Sets are also somewhat disadvantageous because there is rarely a good choice of varieties.

Thanks for the info! I wanted to hear from someone who's really grown onions. I've read about the ammonium sulfate, but all the reviews were about how green it made lawns look. So I wasn't sure if I should use it on something edible. I'm going to look for that and give it a try. I hope I get the results you're getting!

I grew from seeds, mid- and long day onions and transplanted those. I'm hoping for more than quarter sized onions, which is what I got last year. :-)

Yes, the nitrogen from ammonium sulfate benefits the green leaves on the onion. Not commonly understood, but each green leaf on an onion is attached to one ring on the fruit down below. So making the greens on top healthy and robust is about making the onion down below larger. But if you don't know what nutrients are in your soil (a soil test is always smart) you might want to spring for a more balanced fertilizer instead. Onion size will depend on spacing as well. For the largest onions, you need to space them 5-6 inches apart.

What variety are you growing? There are "button" varieties that produce small fruit. Also, be sure to let the onions mature completely before harvest. No one ever says this, but every onion grower should know that the bulbs don't start to expand until the last month or two before harvest. So you're looking at tall and vibrant greens on top for many months before any onions form down below. Onions are ready to harvest when the tops start to fall over.

Urea (46-0-0) is also an option if all that is needed is nitrogen. I usually apply a balanced 13-13-13 when I put out the transplants (Dixondale onions) and then apply Urea every few weeks before an expected good rain or dissolve the urea in watering cans and water the onions

Do you know what varieties you are growing and if they are short day, intermediate day, or long day varieties?

I've already harvested most of my intermediate day types (Candy, Red Candy, and Superstar) as the tops started falling over a couple weeks ago. There are still some of the Candy left to harvest. I am also trying a long day red onion called Red Wing this year and they just started to bulb.

You can get big bulbs from sets just as well as seed but onions grown from sets tend to not store as well as grown from seed, so you heard wrong.

I grow long day onions (zone 4) and can't speak for short day and intermediate onions, but big bulbs require early planting. I planted seedlings April 24th and was 3 weeks late, and also had nothing but rainy cloudy days since the beginning of May so I won't get big bulbs this year.

Big bulbs require many big leaves to get big onions before they start bulb initiation. For each leaf a plant grows there will be an onion ring associated with it so the goal is 12 leaves. Grow 12 big leaves and you will get big huge monster bulbs. My walla walla's have 9 to 10 leaves with half big and the rest smaller by age and have initiated bulbing, they won't be big. My patterson, burnswick and Stuttgarter haven't started to bulb yet and average 8 leaves so odds of big onions are also slim because I've run out of time.

Plant seedlings early, watering well is critical, and enough of the right fertilizers will get you big onions. Dixondale recommends rationing nitrogen over 8 applications (12% each of the total) until the 12th leave and bulb initiation. But instead of all Urea or Ammonium sulfate the best option is 70% Urea and 30% of A. sulfate. Sulfur enables a number of processes you won't get, including utilizing the efficiency of nitrates and you won't get big bulbs. The minimum sulfur recommendation is 25% of the nitrogen you apply, but there is a limit and max's out at a about a 1/3 of the total nitrogen you use over the season. Has to do with high concentrations of many sulfur compounds, and causes bitter excessively pungent onion I believe, and why all professional accredited sources on onion fertilization warn not to exceed the limit.

BTW my wife had an onion figure, it was so fine it made my eyes tear up.

Kevin - I believe most if not all sets sold are long day types. They may grow large bulbs up north where you garden but around here they are lucky to get to tennis ball size. I've had decent sized bulbs from Dixondale Walla Walla transplants but not nearly as big as my brother gets in Wisconsin.

ETA: Interesting on using both Urea and A. Sulfate. Never heard of that one before but I'll have to remember to try that next year. I get some 3.5-4" bulbs with just triple 13 to start and Urea.

Jack, The only yellow onion sets sold here are from Stuttgarter seeds and are long day onions. And you are right, Since the sets need stored for 8 months I don't believe there is a intermediate or short day able to store that long.

Stittgarter was bred and stabilized as an open pollinated variety in northern Europe to grow bigger onions with a shorter growing season and is very popular throughout northern Europe. I've grown Stuttgarter sets and they're good onions but the sets are prone to bolting and pulled my share, and don't seem to store well compared to many hybrids.

So this is the first year I'm gowning them and hope they store just as well as the sets because I want to get away from hybrids and save seed. I'm also growing Burnswick, a red onion also open pollinated from northern Europe and said to also store well. There is nothing special about these onions over any other storage onions.

Oh no! I guess I already blew it by planting too late on June 1. My water wasn’t set up yet so it was later than I wanted. But everything I learn will be helpful, if not this year, in the future. My tomatoes and squash grow fine, but there seems to be a learning curve with onions, at least for me.

That’s really interesting about each green leaf being attached to a ring forming in the onion!

Kevin, I admit that I’ll have to reread some of this to let it sink in.

LoneJack, I would be happy if I got tennis ball sized onions! You’ve already harvested onions? Do you plant in the fall in KC?

My onions are in a 4 x 8 raised bed so not growing on the scale of a lot of you. I used raised bed mix and compost. I add leaves every fall, and this spring I added Land and Sea compost. My water leans alkaline if that matters.

I planted the transplants with some Osmocote, and I did leave good spacing between them.

From Johnny’s Seeds I planted:

Expression – intermediate- day yellow Spanish variety

Red Carpet – organic long-day storage onion

I’m at latitude 41 in northern Utah, so I think intermediate and long-day would be correct?

Maybe I should be growing some of what’s talked about here instead?

Another thing I read: Is it necessary to quit watering for a few weeks before pulling the onions in order to assure they’ll store longer? Not that I’ll have a big amount to store, but I’d like them to keep a while.

Thanks for all the help! I enjoy growing things and always want to get better at it.

With regard to watering, I certainly wouldn't quit a few weeks before maturity. The bulbs need water to expand, and they are expanding rapidly then. The issue is that you don't want to harvest onions that are wet. So it makes some sense to let the soil dry out before you pull. Certainly once the tops have started falling over.

The intermediate variety 'Candy' is easy to get larger onions, decent storage, and easy to get.

Dixondale Candy Onion

Onions are a cool weather crop, can take light frosts, grow green before it gets hot, then mature around the Solstice, so you need to plan that way. As Kevin said, you need to get them growing large plants before full Summer heat. The easiest way is transplants, which can be the half dormant or seedlings.

I try to plant onions in mid March here in KC weather permitting. You should be able to plant intermediate or long day onions in northern Utah.

Long day onions require long days to bulb. If you plant now in June, the long days are NOW. You want the long days to happen when the onions are ready to mature. February/March sounds about right. Short day is very different. I plant in November.

Texas 1015 produces the best tasting large bulb I've found. If you have never had onion rings from Sonic Drive-in you are missing out on a real treat.

So sandy there is very good possibility you will get tennis ball sized onions this year even planting on June 1st. Onion bulb initiation is triggered by day length but also by total heat accumulation from the day they emerged, and your onions have not met the threshold and won't for about another 3 weeks. There are actually two events that must be met in the life cycle of onions before they will bulb, not just day length.

science tracks total heat accumulation using math formulas to create a chart one can use to predict the timing of events of many biological life forms using heat accumulation to trigger an event. The heat unit chart is called "Growing Degree Days" (GDD). To switch on the ability for onions to bulb they need around 600 growing degree days, but this number will change a lot depending on the cultivar grown so I use 600 as a default until I learn or find the actual number.

I pulled up a GDD calculator and used a zip code around salt lake city, (84044) using last years numbers to predict when your onions will bulb based on your planting date. Your onions this year only have 286 GDD's behind them and a long ways to go before hitting the 600 threshold, so your onions won't bulb until mid July. Be a pal and post when they do bulb, you will know when the bulb is twice the size as the neck above them.

Now about my onions. Because it's been so cool here my onions have only accumulated 370 GDD;s. Since the Walla walla's have already started to bulb this tells me the GDD for them is very low but never tried to track them because I didn't care. GDD numbers are a scarce thing to find and I only find them in controlled studies around the world for cultivars would never grow. The GDD can move up quickly if we ever get into the 80's but for now my other 3 cultivars haven't flipped on the switch so they still are producing new leaves. FWIW, GDD calculators are easy to find on line if interested all all one needs to know is the base temperature for the heat accumulating crops or flowers of there interests. GDD is also used to predict bug events like the Japanese Beetles who also uses heat accumulation to emerge. In Minnesota they'll be late this year because of the cool weather.

I think, as Dixondale explains - https://www.onionpatch.dixondalefarms.com/heat-units-in-onions/, growing degree days (GDD) are a schedule for onion leaf production. But as noted, you need to have many healthy leaves to have a large onion. But bulb production is triggered by daylength. So the trick is to have the longer day lengths after the required GDD is elapsed, so there are many healthy leaves. So that's correct that the optimal planting schedule has those two events happening at the same time. Late planting will result in smaller onions, because the foliage hasn't had a chance to develop completely when the bulbs start to form. That being the case, the recipe for larger onions depends strongly on optimal planting time.

I should note that, as I said, I plant out 1015s in November, and harvest at the beginning of May. We've had a couple of EXTREMELY cold winters, and that schedule doesn't change, though the size may be impacted. That is, when daylength triggers bulb formation, there may not have been enough GDDs to maximize foliage.

Emily's article on Dixondale's site is incorrect. My area had 2294 GDD's using 45 as the base last year from April 1st to September 30th. According to Emily my onions would of taken 6 months to grow 11 leaves using 200 units per leave for long day onions. This year my onions have only accumulated 270 Gdd's since planting so they should have one leave according to Emily, she needs to explain where the extra 7 to 10 leaves came from and site her references, she is wrong.
I've read a dozen science experimental studies and reviews of multiple studies that research the topic, give a hypothesis, Validate one study using others and make a conclusion. This is work from accredited professionals in the scientific community using the Scientific methods to express their work and always without exception list all sources of all data they use.
I've never seen any mention of onion leaves dependent on heat units in all the papers I've read. Onions grow leaves as a process all plants exhibit in a vegetative state, and not an event to enter a new growing phase. Emily's article is misinformation and makes me angry, take up heat units? As if they';re nutrients? Nonsense. 2200 GDD to bulb is more misinformation and she doesn';t know what she's talking about.
If you want to learn the true facts about onions read this white paper. ONION BULB DEVELOPMENT. Skip down to section 3.1.3 "Temperature and photoperiod". The author is backed up with impressive credentials and his information includes supporting references to everything he states.

Now I know that one consistent mistake I’ve made is to plant onions too late. One year I had a frost on May 30, which stunted all the warm weather vegetables. That made a big impression on me, so June 1 became my planting date even though I’ve thought about getting onions in sooner. I didn’t realize how necessary that is until now.

I’m getting Lilly Miller ammonium sulphate, 21-0-0, which I’ll put around the onions asap. Maybe next year I should look for a Urea formula of 46-0-0?

We’re in the 90s, 60s at night dropping a little bit in a week. So they are getting heat.

In the flower gardens, I wouldn’t stimulate perennials to put on growth in the heat, so I haven’t given my past onions much more than the starter fertilizer. My misunderstanding of what onions need.

daninthedirt, whatever onions I manage to get, I won’t cut the water too soon. Thanks for that info!

I’ve heard good things about Candy, so I’ll put that on my list. Texas 1015 looks like a short day onion, so while I won’t try to grow it, I can sure put onion rings from Sonic on my list. 😊

Thanks to all of you for showing me the error of my ways when it comes to growing onions. I wish I would have asked a long time ago, lol.

the size of the plant before day legth activation is key

bigger plant bigger bulb. james underword crocket

the victory garden.

That's interesting, kevin9408, but you need to take it up with Emily King at Dixondale. Dixondale doesn't just study onions, they DO onions. They live by onions. Emily has a post-grad education in ag sciences, BTW.

Emily didn't answer her phone yesterday when I called, no one answered. So I sent a message to Dixondale about the inaccuracy of her article. I also posted a comment under the article which is now waiting for the moderator to review the comment. Chances they will allow the comment is near ZERO.

Good idea. Dixondale is pretty responsible about answering questions from users, so I hope you'll be able to make contact.

Down here in okla (zone 7a/7b) I've been experimenting with fall onions planted from sets.

In the early spring I usually plant both onion sets and the plant bundles.

The plant bundles (Dixondale) make my largest onions ( if conditions allow) and the sets are for green table onions (scallions). The sets will mature into small bulbs later into the early summer which I also harvest and store for the winter.

In the fall some places (like my local feed store) will sell the onion sets for fall planting.

I don't know what variety they are , just the yellow , white and red sets.

I've been planting those in the fall around Oct and overwintering them under a low tunnel and then harvesting the following year around late June/July. They do make a sizable bulb but it takes 8 or 9 months to do so. Not all of them will size up , some will bolt when it starts really warming up in the spring . The ones that hold off on bolting makes the bigger bulbs.

And they taste a little different from the spring ones , like a little sweeter from overwintering.

Anybody have any experience with growing fall onions.

Okie HU

Yes, onions are very cold tolerant. I planted and overwintered fall onions both covered and uncovered . The uncovered onions do survive the winter but they tend to bolt more and not size up as big the following spring. The ones I had under cover did better as far as sizing up so they do benefit from covering , even just a layer of mulch during Arctic fronts.

Of course I'm a little further north of Texas.

Okie HU

I fertilize at planting time. I plant early. I set out Dixondale pants I water some. I get kinda huge bubs.

You're doing good there Wayne.

In my locale okla (7a/7b) , I amend the ground with cow manure ( there's plenty of it around here , for free) through the winter after fall cleanup.

Then around Febuary I till in the manure and plant out the Dixondale onion bundles.

I do a wide varitity of onions , . My main ones are Yellow Granex, Candy and Texas Super Sweet.

I also put out other varities , Sweet Red , Red Candy ,White and Yellow Bermurda , Texas Granex. Super Star. also more long day ones like Patterson . Highlander and Red River.

I also plant onion sets ( red ,yellow , white for green table onions) and harvest the small bulbs from those later into the summer.

Like I've said above I've also planted fall onions from sets and overwintered them and harvested them later the following summer.

Okie HU

I also get plants from Dixondale, and they are very helpful when I have questions.

I'm in Northern Michigan so I planted in mid-May.

This year I planted Candy, Alisa Craig, Cippolini, Red Wing and Sterling. I've planted Red Wing and Sterling for several years now and they store really well. Last year's Red Wing lasted until April, nearly 7 months and the Sterling stored about 4 months.

I planted onion sets for 40+ years and got onions, but never very big ones. I get much larger onions with plants. I don't use any fertilizer on any of my garden other than composted cow manure.

This was part of last year's crop of Alisa Craig, that's my oldest daughter, Amanda.

Sterling:

Jack, this was some of the Redwing, I was really happy with it. It was more pungent than the sweets, of course, but firm and flavorful and it got big and stored well.

I do have cattle and so have access to lots of natural "fertilizer". We just push it into a pile and let it sit for a couple of years, then use it on the garden.

Annie

I'm reading everyone's tips and experiences with interest!

Annie, those are some good sized onions! If you have cattle and room for piles, that's the way to do it!

Sandyslopes, I"ve only gotten nice big onions the past 5 or 6 years. I planted onions "sets" before, for about 50 years, and they only got about half the size of the onions I get by planting from seed or getting plants from Dixondale or the local Co-op. We've always spread manure on fields and gardens, so that's not the reason. I save a lot of my own seeds and start most of my plants, so I'm thinking I need to just start my own onion plants in the spring when I start tomatoes/peppers/eggplant/etc. Yes indeed, I feel a "garden experiment" coming on, LOL.

Annie

Those are some really nice onions Annie! It looks like my Red Wings aren't going to bulb any bigger than a tennis ball but they haven't flopped over yet so maybe they will get bigger. Johnny's says they are best adapted to around 43 degrees north latitude and I'm at 38.5 so it was just an experiment to see if I could grow some longer storing reds.

I used to start my own onions and leeks from seed and I would traditionally sow them thickly in 2 lb. yogurt containers on New Years Day and plant out in mid March. I'd think you would start 4-6 weeks later up there. Since I found a local source of Dixondale plants I've stopped growing onions from seed.

Local sources for Dixondale plants are really the cat's meow. You don't pay for shipping. I get a bundle of 50 some plants for a few bucks. Their website doesn't obviously call out vendors, so you might get in touch to ask them who is closest to you who has their stuff. Somewhat curiously, my local source has their onions a few weeks before the regular shipping date from Dixondale.

My local source for Dixondale starts drives their box truck down to south Texas and picks them up from the DD farm. They do the same for their seed potatoes but they get them from a grower in Minnesota.

Jack, I hope your onions keep on growing, those Red Wings stored for 7 months for me, and I was happy.

The past several years I have ordered from Dixondale and they ship to me without charging shipping. I bought Sterling, Alisa Craig, cippolini and Red Wing this year, along with another sweet that I can't remember. They always grow well but their latest ship date is early May. Here we could still have snow in early May, or the frost could still be a couple of feet down so I can't get the garden tilled until it melts a little. I can't keep them unplanted for too long so sometimes they need to go into a container with soil until they can go into the ground. The last couple of years have been mild winters and there were no problems with planting mid-May, but I can't count on it.

So, when you grew from seed you just put the seeds in the container and then separated out the little plants when you put them in the garden? That didn't cause damage to the small plants, with roots getting entangled or such other problems? I was looking at those 366 cell plastic planters, I already have lights, mats and shelves because I start around 250 other plants, some for me and some for a couple of friends, mostly tomatoes, head lettuces, peppers, eggplants and a few flowers. Greenhouse/nursery plants have gotten so expensive that I'm expanding next year and planting more flowers, this $5 for a single plant in a pot and flats now being a dozen plants for $18 is not working for me!

Annie

Dixondale says that shipping is included in the price. You're paying for shipping, but not separately. That's why it costs $16/bunch if I get them mailed from Dixondale, and a $3/bunch if I pick up locally. Shipped from Dixondale, most of the cost IS shipping.

Annie - I just pull the whole clump of onion seedlings out of the yogurt tub and then gently wash the potting mix off of the roots which makes them easy to separate to plant out. I plant around 50 seeds in each tub and grow them for about 10 weeks. After about 6 weeks the seedlings are getting about 5-6" tall and I start trimming them back to 4" every week or so. A 5-6" deep pot would work just as well as a yogurt tub. My wife used to feed our small flock of chickens yogurt as a treat so we had a bunch of tubs laying around.

Thanks, Jack! I have lots of miscellaneous "planters" hanging around, that would be a good use for some of them! Now you know I"m going to have to try it, LOL.

Daninthedirt, I order from Dixondale and there is a price break the more bundles I buy. So, this year I bought five separate bundles and I planted them all. I do sell "overflow" vegetables to the B&B across the street, so none go to waste. A couple of neighbors add their orders in with mine and the result was that this year they cost $6.50 a bundle shipped, which was not bad but that timing with the shipping is sometimes a

problem. None of the local greenhouses and nurseries had any onion plants at all, only sets. The local farm co-op had plants but they looked terrible, like they had been sitting in the boxes on the shelves for longer than they should have.

More reasons to grow my own!

Annie

Update: After fertilizing just once with the 21-0-0, I did get decent sized onions! Not quite tennis ball size, but bigger than a golf ball, so I'll take it! I probably should have fertilized again, but I didn't get it done. Next year I'll shoot for planting earlier.

Again, thanks for all the helpful advice to help me grow better onions. Not there yet, but I'll keep on trying.

Be aware that soil nitrogen leaches effectively. So a single application of ammonium sulfate or urea won't do the trick. Need to amend regularly. As I said, I throw some on every three weeks.

A good start considering how late you planted them. Reminds me of my trials 20+ years ago buying sets, planting in mid jun then wondering why they are not big.

These onions below are not mine, they came from my neighbors garden. Mine were pathetic in size with bad taste so I trashed them but I usually get onions like this too.

The reason my onions failed was because of the difference in soil and the huge amount of rain we had between May and July. I have deep black dirt that drains slowly so I usually raise the beds 6" but didn't this year and of course we got dumped on with rain. my onions sat in standing water for days between rains and the roots drowned out stunting the growth. Onions will grow new roots and a beneficial trait which allows onion plants from dixondale to be partially grown and shipped, but my roots continuously died off from to much rain for over two months.

My neighbor grows in fast draining fine sand so he didn't have a drainage problem but does have a nitrogen leaches issue so he needs to fertilize every TWO weeks and I know he has no 21-0-0. I never asked him what he does use but I do know has Urea and 10-10-10 so could be either one, and I'm starting to question the need for so much sulfate because his are really great tasting onions.

Sulfates give onions their taste. Why would you want to under-sulfate them? Of course, you could always ammonium nitrate them or urea them, if you didn't like your onions very oniony.

dan, I'll make a note to myself about fertilizing every three weeks. Things got away from me this season. And interesting that sulfates give onions their flavor.

kevin, I can't relate to ever having that much rain being out west where I am. That's too bad about your onions this year, but it looks like your neighbor shared with you. I put down leaves in fall and compost in spring, so I hope the bed has a good balance of nutrients even before adding 21-0-0 sulfates, but even one dose seemed to help this time.