Onion from Seed-- My First Time

yutopia(6B)January 13, 2014

Hi All,

Newbie to starting onion seed here. I'm also new to soil blocks, which I am excited to be using for the first time this year.

I have read that Eliot Coleman recommends grouping onions in fours for planting. I'd like to start my seed in groups of four so that when planting time comes (I believe mid March for my Pittsburgh, PA, garden, but correct me if I'm wrong) I can just plop my soil plug containing four thin onion starts directly into a planting hole, where they will grow all summer into large bulbs. I will start my seed toward the end of this month so that the starts will have 6 weeks under lights in my basement.

I have seed for Southport Red and Ailsa Craig.

My goal is to simplify the process as much as possible. I'd really like to avoid transplanting tiny onion seedlings. I am concerned about the tap root however-- I can put sand in the bottom of my seed starting tray so that a tap won't be air pruned by the end of the soil block. I am planning to use the medium size soil block, although it would be awesome if the smallest size would work.

I'm looking for more experienced onion growers to tell me what's wrong with my plan and to give feedback on how onion seeds do in soil blocks.

Thanks for looking and hopefully responding, and happy growing!


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gjcore(zone 5 Aurora Co)

Starting 4 in a small container and growing under lights will be okay but you don't need to worry about taproots. Onion seedlings can handle being transplanted easily.

The way I start onions (which will be in a few weeks) is to fill an entire flat with the best quality potting soil I can get which is usually Fox Farm Ocean Forest. Then I'll sow about 100 fresh seeds in each flat. I'll let them grow under the lights until sometime in March when they start getting used to outdoors. Maybe I'll put them in a coldframe for a month or so. When it's time to transplant I'll take the entire flat, a kitchen spatula and a 5 gallon bucket 2/3 full of tepid water into the area they are going to be planted to.

Taking the spatula I'll place onions and soil into the water and gently swish them around. Next I'll pick the onions out and start laying them out in the general area and plant them a couple inches deep. Then gently rinse the seedlings with a watering can.

    Bookmark   January 15, 2014 at 5:59PM
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seysonn(8a WA/HZ 1)

Onions do NOT grow tap roots.
Onions are the most transplant and mishandling tolerant plants that I know. You can leave the seedlings in some place for days and come back and plant them they will be fine.

Sure, you can try to plant them SEED BY SEED at exact spacing and all. But that is not how it is done.

If you still don't wan to be bothered with transplanting you can sow many times more seeds in the same plot or pot and later on thin them, leaving just enough at the proper spacing.


PS: I can thin them as they grow and used them as scallions.

    Bookmark   January 16, 2014 at 10:55AM
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" I can just plop my soil plug containing four thin onion starts directly into a planting hole"

I would give the onions more room to bulb up. I try to keep them separated by 6" or so. Ailsa Craig are not small, I don't know about the other kind. They are fairly robust as said previously. They transplant well. I try to put them just deep enough so the stay vertical, don't fall over.

I start about 75 seeds in a deep "lunch meat" tub about 3.5" x 7" at the biggest. But then you gotta soak them to separate the roots come April (in zone 5).

    Bookmark   January 17, 2014 at 7:31AM
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theforgottenone1013(MI zone 5b/6a)

Having several plants close together is called multi-sowing. You can use it for onions, beets, leeks, round carrots, etc. What you do is plant several seeds next to each other and you space the clusters (bunches?) farther apart than you normally would for a single plant. The result is more plants BUT the plants themselves will be smaller. So instead of getting one large bulb (for onions) you get 3-4 small to medium sized ones.

Just wanted to point that out. The others have already given you good advice.


This post was edited by theforgottenone1013 on Fri, Jan 17, 14 at 16:19

    Bookmark   January 17, 2014 at 4:18PM
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I think multisowing is great for some things, but not big bulb onions like the varieties named here. I would perhaps plant cippolinis in threes, but otherwise think the time spent separating seedlings and planting them at proper spacing is time well spent.

    Bookmark   January 18, 2014 at 8:49AM
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I would definitely separate out those seedlings and plant them individually. As mentioned above, onion seedlings are very tough, and will pop right back up after transplanting. I grew A.C. last year, and planted them about six inches apart. They grew great, and rewarded the space. Scallions are happier in those 4-6 bunches, but even they grow better individually.

With all respect to Eliot Coleman, I'd stick with dedicated onion growers for advice, and not a guy who specializes in pushing season length. The people who grow the best, most productive onion gardens space 'em.

    Bookmark   January 27, 2014 at 2:57PM
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How do you guys thin them? Would snipping them prevent them from coming back? Or would you need to pull them out?

    Bookmark   January 30, 2014 at 6:51PM
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seysonn(8a WA/HZ 1)

How do you guys thin them? .^^^^

I start them in flats , then at some point pull them all up and transplant them at proper spacing.

But to answer your question: If they happen to be to clumped or close, Just dig them up, separate them and replant them at the right spacing. OR, if you have lots of them already and have no place to transplant, just keep what you want and pull the ones that are crowding out and enjoy them as scallions.
I usually plant them twice as close and use about half of them as scallions/green onions.

    Bookmark   January 31, 2014 at 8:34AM
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I am growing from seed for the first time also. My little ones are 2-3 inches tall, and are under lights in my basement. They look to be doing well, but it's pretty warm under there.

Would they be much better off if I moved them to a cooler place? I have a cellar that ranges from 45-50 degrees for the next couple of months.

This post was edited by Creek-side on Mon, Feb 10, 14 at 22:14

    Bookmark   February 10, 2014 at 10:10PM
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Creek, what type of lights are you using? They don't sound like cool fluorescent lights if "it's pretty warm". 45 degrees (F) is warm enough for onions; it won't bother them. Just don't burn them up with incandescent bulbs! If you have them close to incandescent lights, you might want to put a slow fan on them to keep them a little cooler! Just enough air flow to make them wiggle.

My onions are at about 70 F (in the family room under fluorescent lights) which works well. Next week we may have a few days above freezing. If so, they are going out doors with a little protection during daylight hours. (They are not hardened off.)

    Bookmark   February 10, 2014 at 11:59PM
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Not to worry, mine are under fluorescent lights also. I like the fan idea; I do that with all my other seedlings, but it didn't occur to me to for onions.

    Bookmark   February 11, 2014 at 6:43AM
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seysonn(8a WA/HZ 1)

I started a batch, in a flat, last August. Then I replanted them in pots. Finally transplanted them in ground. They have been out there all winter long, temperatures dipping to mid teens. They have not yet been growing much but as soon as it warms up a bit , I am sure they will take off.

So my point is that, you don't have to grow onions inside , under light for a long time. JMO

    Bookmark   February 11, 2014 at 5:08PM
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Donnie_Mac(Ks 6A)


I use the 2 inch soil blocks. Soil blocks work great. As others have mentioned for large onions only one seed per block. I grew Candy in blocks and they were the largest of all the onions I grew last year.

Start your seeds in the blocks and then when ready plant out spacing plants (not blocks) about 4 to 6 inches apart. Plant just deep enough that 1/4 inch of soil covers the block. It's that simple.

There is one down side to blocks. A 1020 tray will only hold 36 two inch blocks. I want 200 storage onions this year so for me that would be 6 trays. That is half of my light area.

From your post you are new to blocks so I will tell one thing that helped me. Get web trays and put them into the 1020 trays when you make your blocks. To bottom water I take another 1020 tray and put water in it and then lift the web tray containing the blocks and put that tray into the water. Let it sit till the blocks absorb the water then transfer the web tray back to the original tray. That makes it very easy to water the blocks.

Good luck,
Donnie Mac

    Bookmark   February 11, 2014 at 10:14PM
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Are there any important aspects to pruning the seedlings? Mine are now about 4 inches tall, and the very tips are drying out, maybe a quarter inch or so, nothing big. Someone told me to prune them back to a couple of inches.

    Bookmark   February 20, 2014 at 6:51AM
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As long as my seedlings are indoors under lights, I trim them to 4-6 inches. Right now the leaves you are trimming are temporary leaves anyway. The first leaf always falls over and shrivels, and sometimes the second one, too. Starting with the third and fourth leaves, new growth should have more substance and won't need trimming.

    Bookmark   February 20, 2014 at 9:03AM
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I am a long time gardener but new to starting leeks from seed. I plan on starting seeds in six inch pots filled with good seed starting mix. My question is, should I start the pots on a heating pad or start them at a lower (65 degree) temperature? Is March first about the right time to start seeds indoors in zone 6B?

    Bookmark   February 28, 2014 at 9:45AM
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These are my onion seedlings about 1 month old now just before their first trim back to 4 inches. Talon, Norstar and red zeppelin

    Bookmark   March 22, 2014 at 9:00AM
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jonathanpassey(Utah z5)

Its my first time too. I appreciate the previous responses. I am learning a lot.

I am growing a variety called 'Yellow of Parma' that I bought from seed savers. It is supposed to be a large yellow onion that is good for storage.

i planted mine on the 15th of February and many of them are about the size of a bic pen now. this picture is from last Saturday.

I am planting them outside this Saturday. I think I put down maybe 110-120 seeds and I will have 85 sturdy transplants and if i planted the skinny ones too i'd have close to 100.

you can see i have been trimming them fairly often. they just seemed a bit more manageable that way and i had heard that it might even help the plants.

    Bookmark   April 1, 2014 at 10:03PM
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