Starting Your Onions and Leeks from Seed

High Mowing Organic Seeds e-letter today is on the best techniques to start onions from seed. I use these same techniques except for item 3 - instead of covering the seeds with soil, I cover them with medium vermiculite and then spray the vermiculite with water to fully moisten it. Vermiculite will not cake and harden like soil does, and allows the seeds to sprout easier.

Here is their article in full:

1. Moisten your potting soil. Add a little bit of water and mix with your hand, adding more water gradually until it feels just barely moist (but not wet or soggy).Fill your tray or pots with the moist soil to within 1/2" of the rim, tamping down lightly as you go.
   
   
2. Sow your onions or leeks seeds on the surface of the soil, being careful not to crowd them – there should ideally be 2-4 seeds per cell or square inch, and no more than 10 if you’re trying to stretch your space. The more densely you plant them, the thinner and more vulnerable they will be at planting time. The goal is for them to be almost as big around as a pencil by planting day.
   
   
   
3. Cover the seeds by lightly sprinkling 1/8-1/4” of potting soil over them, then gently water in.
   
   
   
4. Cover your tray with a propagation dome if you have one, to hold in moisture and place the tray on top of a seedling heat mat.
   
   
   
5. Move the tray from the heat mat and place under lights once the seeds have germinated. Water gently when the surface of the soil becomes dry to the touch.
   
   
   
6. Gradually raise the lights as the plants grow, so they are 1-3” from the top of the plants. When the plants reach 5” tall, use scissors to trim them back to 2” as this will encourage them to grow thicker and stronger. Pro tip: the onion trimmings are delicious in sandwiches & soups.
   
   
   
7. Begin hardening off your onion starts for transplanting.
   
   
   

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OG, since you and I live at the same latitude, and since my onions were a total fail with direct sowing in late April in 2020, when do you start your onions indoors?

Brian

Brian, I start them on heat mats indoors early- to mid-February, and transplant them into the garden beds mid- to late-March.

Note 1: If you are direct sowing the seeds in the garden, the soil temperature needs to be 70ºF in order for them to germinate.

Note 2: If you have cold hardy onion seeds, such as the Nebuka Bunching Onions, you can direct sow the seeds in September and leave them in the garden over the winter to get a head start on spring onions.

I live in snowy, cold, Chicago, so I normally wait until early March to start my seeds indoors. Ive found it much easier to start seeds with regular a soil mix and I simply place the tray over an indoor heating vent the entire day. And with the sun coming in it’s just about perfect. I also have the plastic lid on, but I don’t seal it all the way. You do need some air to come in, otherwise you will have the obvious problems with the elevated heat and moisture. N growth appear in about 10 days

I let them grow all the way until planting time in the regular pots. Then take them outside towards the end of April and separate them and I do let them sit in an uncovered area in the shade or semi shade until they actually harden over, about 5-6 days.  

The greens on top will brown over but the onion bulbs will start producing roots. By the time Mother’s Day rolls around I have them in the ground and they grow beautifully until harvest

I live north of Seattle Wa, and start them mid february.  I use potting soil in a flat and sprinkle the seeds in and cover lightly with a thin layer of soil.  I have a heating pad for starting seeds and cover with a clear plastic top.  I let them get about 5" long and about 1/8th inch in diameter then plant them outside.  I've found that planting onions from seed is the best way to grow onions and I have great luck with Ailsa Craig onions.  mix some year old chicken manure with the straw in the bed and they grow big.  they store well also.

Bump!  Just brought mine up from lights in basement.  I have celery in with them, might move the celery as it takes sooooo long to germinate, the onions will start hardening off but I want to get a trim in first! 

Thanks for the post, OG!

Scorpio Rising wrote:Bump!  Just brought mine up from lights in basement.  I have celery in with them, might move the celery as it takes sooooo long to germinate, the onions will start hardening off but I want to get a trim in first! 

Thanks for the post, OG!

I'm bringing mine out today as well. They've done super well under the lights, but they're getting too tall. Do you trim the tops?

Brian

Brian, I trim my onion seedlings several times as they are growing under lights. I trim them back to about 2" tall, and use the trimmings in salads or stir fry recipes.  My first batch of bunching onion seedlings will going out into the garden this afternoon, and then I start another batch of seeds indoors for the second batch to go into the garden when we start harvesting the first ones.  We have been eating the Red Welsh Bunching Onions (perennials) from the garden, but we have pulled about as many as we can for this spring.

The seedling are ready for transplanting, but need be trimmed back before they are taken out to transplant.