Growing onions from seed

Hi I always grow onion  from 'sets', i.e small onions grown commercially the previous year. I would like to start from the seeds instead.  That's cheaper and more sustainable. Ability to save seeds is an extra bonus.

My question is how? If I plant seeds indoors in the spring will they be full size by August?  Or should I plant the seeds outside then harvest my own 'sets' for next year?  

Those of you who grow from seeds how do you do it? Please mention where you live, if its not on your profile,  as I think climate must play a role .

Thanks everyone!

I plant potato onion seeds in the spring and then harvest some of them in the late summer of the following year. I know some folks in my area plant both seed and tuber in both the spring and fall, just to maximize breadth of genetics -- allowing the plants to be accommodated.

I start my onion seeds inside in January then transplant them outside in April.

Christopher , I had never heard of potato onions before.  I love alliums, and will keep an eye out for them.

Aimee, so by doing that you get full size onions the same year?  What climatic zone are you?

I am in zone 5A.  I get big beautiful onions the same year as long as I start them in January.

Thanks Aimee!

I am in 7b but have only grown onions from seed for the first time this year. No expert here. 😌
I started the seeds inside in January in a flat deep tray (I think i may wait until February this year) I planted out in April.
Some of mine were too delicate I think for a hard frost but most made it through to produce decent looking red onions.
I want to plant out a little later to avoid a frost and I will definitely plant more…. Not so close together. 😂

I am in Zone 5b. I am going to try planting onion and leek seeds directly in the garden this weekend and see if they come up next spring and survive spring frost.  So many plants come up as volunteers so why not? If they dont then the loss of a few bucks in seeds wont kill me! If they come up I'll post pictures next spring.

I did seeds starts inside for the first time this year. The onions were started in January and planted out over a month+ through May and June. ( life got very busy and the garden suffered)

This was a trial year on our new property and I didn't have the time or energy to do much in terms of feeding, aside from one small test square. The onions in the desodded and rabbit manure topped bed were the only ones to do significant growth. All ended up as very large green onions. Tasty and mild but no bulbs. Almost everything else in that bed, aside from the purslane, drowned.
Many of the others survived, but even when I dug them out in the last few weeks, they were barely bigger than when they went in the ground.

I'm planning on trying starts again this year and hope to get the truckload of manure I want in and spread about so we'll see how it goes.

There was a great book in the local library about onions, from which I learned the following - "there are long day and short day varieties"
So if the wrong type is chosen, then the bulbs won't form.  Just chased up this site for more information:-
https://bonnieplants.com/blogs/garden-fundamentals/which-onion-is-right-for-you

I'm south of Capricorn, so garlic grows for me over winter - still warm by your standards, but fewer hours of daylight.   Green onions (spring  onions?) will grow anytime.   Haven't delved further into the bulb varieties yet., but the one time I planted seed, it was the 'wrong' type.  Flowering green onions really attract the bees which makes it a good idea to leave a couple unharvested . . .  noticed that the bees were dashing off to the tomatoes . . .

Jill is right about the day length,it does matter what type onion you plant depending on your locale.I have planted seed in January and early February   with the same results,pretty much all onions make nice big bulbs.I planted sweet spainish and ailsa craig,both made nice bulbs.Im in the"intermediate zone" but i always plant southern onions with good results.I sow seeds in big 10 gallon or larger pots just so i can plant an entire pack in one pot and not get too crowded.

Remember that the winter solstice might determine whether your plants make bulbs or make seeds.if planted too early before the solstice they might just go to seed,wait til the solstice to sow seed to make bulbs.

Just want to add that you might want to plant some scallion seeds too.
They come up earlier, they produce bunches and can be picked all summer.
And they can handle the cold so I still have some in the ground, growing well.
You can even put some in dirt, take them in the house, set them next to a cold window and cut tops from them in winter

I just put them in a cup of dirt. They grow like grass and I separate them to plant them.
I thought; plant one scallion and you get one scallion.
But one scallion plant will turn into a bunch of scallions.

I didn't even plant onions this year, just scallions.
But next spring I will probably start onion seeds in a cup of dirt too.
Onions and scallions take a while to get big enough to plant so are one of the early things, they grow slow and can be started in January.

I havent grown scallions from seed just from bulbs.Do they reach full size in the first year when grown from seed?

I grow shallots every year, variety called Ed's Red, very easy, like clock work. zone 5-5A

Just stepping foot into January, this is a good time to consider starting onion seeds for people in similar climates to my own. I have some starts ordered for the spring, but I want to try and grow my own. If I have success, I know next year not to get starts as I can start seeds for quite a bit cheaper.

Any tricks to successful growth?

Yes! It soon begins again,finally past the solstice now and spring will soon be upon us,I have seed ready to sow but will have to wait til the weekend.I had some seed i saved over from last January and planted them in early October.They are doing well in a unheated hoop house,i was experimenting to see how long the seeds were viable,and almost all germinated.I was happy with the results and now i am going to see how they survive with no heat,perhaps they will go to seed if they make it til spring.

Timothy they like rich soil and need nitrogen to get a good start,just dont pot them up.Sow them in a big enough container so the seed are close to each other and wont get root bound before spring planting.They seem to do just fine at half inch spacing but need to have a deep pot for root growth and good drainage.

Shookeli Riggs wrote:I havent grown scallions from seed just from bulbs.Do they reach full size in the first year when grown from seed?

Yes, you will get to start picking a few scallions, I think by July. And they will all be good by the end of the year.
they need weeded a couple times. Once when they are young because they are so small,
then weeded and mulched once more when the weeds start to come up again.

So you have been planting one scallion bulb and having it turn into a bunch?
I've been doing the same with seeds that I started in february,.. but wished I'd have started them in January.
Last year I even had some scallions flower so they might be able to produce viable seeds. I'll find out soon.

I have started onions from seed that were planted in Jan they got going but I don't have much luck/skill at growing nice big onions.

Hi guys, I live in zone 10b and I'd like to share my experience. I've been experimenting with onion growing for several years now and last year's crop turned out really good. I have been starting my short-day onions by sewing the seeds in 4" pots around September 1st. I have been planting garlic into the ground around this time as well. By mid October the seeds have sprouted and I plant them out into the garden that has been given some compost and rock phosphate. This year I spaced them 8" apart, last year I did 6"with nice results. I'll spread some compost over them this winter and again in early spring if I have enough. I've been harvesting them in June and onward.

I'm having a hard time with some of them getting black mold while being stored, both tied on an onion string and stored in a reusable potato bag. This year I'm really going to focus on the drying and curing process.

Does anyone have a good method of harvesting and drying onions for storage without them developing rot?

Craig i do get a bunch by growing from a bulb,just like garlic,i might have a try with seed to see how well they do.

Hi Randy,welcome to the forum! I get some with black spots of mold or mildew maybe  on them when drying too but only on the outer skins,i peel back a few layers and most are ok,i always have some rot as well,might be a root maggot causing it im not sure.

I hung mine in my unheated hoophouse this year and they kept well.i still have a few ,and some have started growing so i replanted them for fresh green onions and maybe seed if i let them go that long.

I've never grown bulbs before but really wanted to give garlic a go this year.
Somehow, I failed to both count the bulbs I purchased and failed to consider the spacing I'd need when clearing.
I ended up preparing (mowing & broad forking) an enormous space and not having enough garlic to fill it.


Garlic only planted up to those sticks/that plank - and then were covered with organic straw for a Ruth-Stout-esque planting

As you can see, this left a good deal of space to fill. So I went to my seed collection and found onions!


Those ended up being planted out with rough spacing to fill everything not mulched in the above photo, and mulched below:


Again I still had some space left over... going back to my collection I found broccoli seeds from a microgreens business I bought in the pandemic and ended up not moving forward, several quarts of seeds several years old.
I scattered a dozen handfuls over the remainder of the plot and tucked it in for winter:


I read that this ought to work, but who knows. I'll report back on how this grows out (if at all)!