Starting Onions from Seed

Here in Zone 6 it is time to get onion seeds started indoors so they'll be ready for transplanting into the beds mid- to late-March.  I started mine yesterday in 72-cell trays - 5 seeds per 1" cell - which will be grown for spring or green onions. They are sitting on heat mats with a plastic dome over the trays. Anxiously waiting to see green sprouts appear!  

Onions seeds are extremely easy to start, and much less expensive than sets. But, onion seeds don't store well and must be fresh each year for reliable germination. For those that have never grown onions from seed, High Mowing Organic Seeds offers this easy to follow guide:


Here are some helpful allium seed starting tips:
1. Moisten your potting soil ahead of seeding

2. Fill your tray or pots with soil to within 1/2" of the rim, tamping down lightly as you go

3. Sow your onion or leek seeds on the surface of the soil, being careful not to crowd them

4. Cover the seeds by lightly sprinkling 1/8-1/4” of potting soil over them, then gently water in

5. Once the seeds have germinated, move the tray from the heat mat and place under lights

6. Water gently when the surface of the soil becomes dry to the touch

7. As the plants grow, gradually raise the lights so they are 1-3” from the top of the plants

8. When the plants reach 5” tall, use scissors to trim them back to 2” as this will encourage them to grow thicker and stronger

9. At this point, you can begin hardening off your onion starts for transplanting

Any advice about bulb onions?

donnainzone5 wrote:Any advice about bulb onions?

I haven't planted onion sets for a number of years, since the ones we grow are primarily for spring or bunching onions - many of them are diced for freezing to use in winter recipes. Onion sets are best planted to develop into bulbs for winter storage. One of the major problem with onion sets available in the big box stores is that there is no indication of what variety they are. Are the long day, short day, or intermediate day? They are labeled as "red onions", "yellow onions", or "white onions", with no indication of variety.

When I did plant onion sets, I planted them about 4 weeks before the last frost date so that they had plenty of time to develop for harvest before winter.

So far, I haven't had any luck with onion sets, probably because of the issues you mentioned.  That's why I thought I'd try my hand at starting from seed--again.

OG, thank you for this post.

sanderson wrote:OG, thank you for this post.

 


The onion seeds are planted, and sitting on heat mats under lights. They'll be ready by Spring.   

I started onion seeds for the first time this year. I started them 10 days ago and they are already under the lights and about 2" tall. I wonder how often I can cut them back before they go outside; I am in zone 4b. I probably should have waited longer before I started them, but I was too impatient. I also started leaks and celery last week.

dlabrie wrote:I started onion seeds for the first time this year. I started them 10 days ago and they are already under the lights and about 2" tall. I wonder how often I can cut them back before they go outside; I am in zone 4b. I probably should have waited longer before I started them, but I was too impatient. I also started leaks and celery last week.

I let them get to about 5" high, and then trim them back to about 2". I do this multiple times until they are ready to harden off and plant in the gardens. BTW, the clippings are great in salads.

I'm in Zone 6, and I plant them in the gardens in mid- to late-March. They are very frost tolerant and do well during the cold spring weather.

The onion seeds were planted 6 days ago, and they are growing fast