Do you fertilize your onions? How much how often?

I've been realizing that our onions lately have been running out of nutrients (whatever they need happens to be in 24-8-16 Miracle Gro, fortunately). It looks like my options (as far as I know) are to fertilize them, and turn up the soil before planting next time to bring more nutrients from below up.

They seem to need fertilizer more when it's hot.

I'm surprised this hasn't been answered, and I hope an expert chimes in to do so. I watched a .edu zoom on the topic a while back, just a blank now.

At my volunteer garden, the soil test showed only nitrogen was needed. As far as I know, only that "lawn fertilizer" 26-something-0 was applied, one time. We've been pulling onions for two weeks, same size as last year, and it has been very hot. In fact, today a second planting of onions plants are going in to fill the empty spots. I'll find out if they are going to broadcast more fertilizer.

- Lisa

I'm surprised this hasn't been answered, and I hope an expert chimes in to do so. I watched a .edu zoom on the topic a while back, just a blank now.

At my volunteer garden, the soil test showed only nitrogen was needed. As far as I know, only that "lawn fertilizer" 26-something-0 was applied, one time. We've been pulling onions for two weeks, same size as last year, and it has been very hot. In fact, today a second planting of onions plants are going in to fill the empty spots. I'll find out if they are going to broadcast more fertilizer.

- Lisa

Well, I am no expert by any means but when I started trying to grow onions I did a lot of online reading about it. Then I put together my own grow sheet, copying/pasting things I found. Like everything else, different sources vary a bit in what ferts to use and how often. For sure all sources said onions are heavy nitrogen feeders. Some bullet points that I try to stick to:

From Texas A&M: http://aggie-horticulture.tamu.edu/arch ... ONGRO.html

"Fertilization of onion plants is vital to success. Texas A&M research findings indicate that onion growth and yield can be greatly enhanced by banding phosphorus 2-3 inches below seed at planting time. This phosphorus acts as a starter solution which invigorates the growth of young seedlings. Banding phosphorus, such as super phosphate (0-20-0), 2-3 inches below the seed involves making a trench 3 inches deep, distributing one-half cup of super phosphate per 10 row feet, covering the phosphate with soil, sowing seed and covering lightly with one-half inch or less of soil. Once established, onion plants should receive additional amounts of fertilizer (21-0-0 - Ammonium sulfate or Ammonium nitrate) as a side-dress application every month."

From Fine Gardening: https://www.finegardening.com/article/t ... own-onions

"Onions need phosphorus and potassium for root development during the first two to three weeks after planting. Just prior to planting, apply a balanced fertilizer, such as 10–20–10, close to where the onions will be planted. Three weeks after planting, the root system will be established, and a biweekly feeding of a nitrogen-heavy fertilizer, like 21–0–0, will keep the foliage growing and a deep green color. at this point, a new leaf will emerge every two to three weeks. Once the transfer of carbohydrates, or bulbing, begins (you’ll see the soil begin to crack around where the bulb is forming), the growing cycle is complete. no further application of fertilizer is required."

From Our Stony Acres: http://ourstoneyacres.com/seven-easy-st ... ing-onions

"Onions like nitrogen! If you have good healthy soil they should do fine. But to get a bumper crop of big bulbs you will need to fertilize. I like to water my onions a couple of times a year with a mixture of fish emulsion. 2 tablespoons in a gallon of water is good. Or you can side dress your plants with an organic nitrogen fertilizer."

Personally I do the A&M method using super phos in a trench method but go 4" deep at the rate of 1/2c/10' row under where my seedlings will be planted a week or two before planting. Then I come back with the ammonium sulfate once a month since that's what I use for the corn and have on hand. Both crops like a little sulfur.

I was waiting for experts.
But yes onions like nitrogen.
I use 13-13‐13 on just about everything.
Onions are like grass when it comes feeding time.
The faster you can get them to grow the bigger the bulb will be due to leaf count.
Then the weather permitting and no crazy temperature swings when the daylight hours reach the maximum for your day length onions they will bulb.
If they think they have gone through two winters with hot spells during the winter they will go to seed the first year.
Right now my area isn't worth a hoot for growing onions with big bulbs due to wild temperature swings.

Same here with the temp swings, causing onions to bolt most years. Here we plant onions in October so they finish before the longest day of the year. I still try every year and can get some before they bolt. They'll never get real big but that's OK.

High nitrogen seems to be the trick. I think the ammonium sulfate I use is 30-0-0 and I get it at the local feed & seed. Instead of the super phos under the plants I sometimes just till in 5-10 15 pre-plant for a smaller phos boost, then come back with the 30-0-0 for the first real fertilizing.

Fall '20 I planted Texas 1015Y. They didn't do well at all come last spring. Last fall I tried the Texas Early Grano. They did well this spring and were pretty sweet.

I’ve been successful growing big onions the last few years.
The keys are:

1. Full sun
2. Weed free
3. Transplant size
4. Adequate spacing
5. Sufficient watering
6. Fertilization

I plant Dixondale onion plants and I also start my own seeds in January. Full sun (No trees) is a a major key. The onions at my community garden (former farm) are bigger than the ones I grow at home. The difference is the farm get sunlight starting around 5-6 am but at my house, it’s not until 9am due to some trees.

I get my Dixondale plants at the end of March. I put them in rootrainers 5” deep with compost. I don’t transplant them into my garden until the end of April. Until then, they’re in my greenhouse during the day and brought inside the house when the sun goes down. This helps them get a fast start.

I ensure my onion beds are weed free. My onions are the biggest in the community garden because I’m very good at weeding the beds and giving them the head start in the greenhouse while others are planted direct in the ground and have to fight early spring cold weather.

I fertilize every 2 weeks with 10-10-10 fertilizer. This means two applications because my onions start to bulb in early June.

There was one year when I fertilized only once. I still had huge onions

Onions are nearly as needy as corn for adequate nutrients and moisture especially during early bulbing.

@ponyexpress what is your row spacing and space between plants?

Bower wrote: ↑Sat Jul 23, 2022 7:49 am @ponyexpress what is your row spacing and space between plants?

6” apart in a row. I think each row is 12” apart. I’ll have to measure to confirm. In my community garden plot, I have four rows. There might be 24 or 36” separating the two sets of rows. I’ll try to measure later

Thanks @ponyexpress I'll take the 12 inch as a guide.

I just saw my friend's garden last night where he's growing the same onions from Dixondale in full sun but with one difference. His garden beds are almost pure black gold mulch. Every year, he piles shredded leaves on top of his beds.

His onions are bigger than mine, especially his Ailsa Craigs. He doesn't know what do with all of his Ailsas as they're just two of them to eat the onions and they don't store as well. I told him that next year, he should only plant 20 Ailsas and we'll split a bunch with a few people.

Send the extras to me.
I'll eat them.
I average an onion a day.

My daughter’s boyfriend’s family like the onions with small bulbs for grilling.