Onions Seed seed starting

Onions – Helping A Reader – Should She Plant According to Directions on the Package?

I received an email today from long time friend and reader, Toni, from Oregon.

She writes:

I’m looking on my onion seed packets. These are seeds grown for companies locally. They all say to plant the seeds directly into the garden from April to mid-July. This is really confusing me. Do you think I should try doing that?

Because of your direction in blog posts on growing onions I first attempted to grow them. Now I LOVE growing onions.

The reason the information confused me is because I have a very significant number of onions bolt and I wonder if transplanting them is causing them to bolt?

I can understand why these instructions would be confusing.

It’s almost a guarantee — especially knowing that seeds are grown specifically for that area — 95% (or more) of gardeners will take the instructions to heart and sow directly into the garden anytime from April to mid-July. Large, wonderful onions that will cure and store for winter will be what they’ll expect as results. More than likely they’ll be disappointed.

Onions Take Growing Time Before Bulbing is Triggered

In order to get mature onions that can be cured and stored, they have to be in the garden long enough to grow large roots and tops before daylight hours and warm temperatures trigger bulbing.

Toni’s location is far enough north (Latitude 45.356507º N) that long day onions are the only ones that will do well there.

Long day onions take 14 to 16 hours of daylight (coupled with warmer temperatures) to trigger the bulbing process.

14 hours of daylight will start in her garden on the 25th of April, 2018 and gradually increase to 15 hours (her maximum amount of daylight hours) on May 18th.

Since we don’t know the variety’s exact number of hours needed to trigger bulbing , let’s assume that it’s a minimum of 14 hours which starts April 25th. If temperatures are warm enough (at least 60 to 70 degrees) bulbing will be triggered on that date.

That means the onions already need to be up and growing at least 13 weeks prior to that for the largest possible onion.

If Toni starts her onions now, her seedlings can be transplanted to the garden 6 to 8 weeks prior to the last frost date. Since that’s April 1 for her location, she’d be transplanting the seedlings February 1 to 15 for best results.

Less Leaves (Tops) When Bulbing is Triggered Means Small Onions

Following the instructions on the package and sowing directly into the garden in April will probably get good germination. But the seedlings would have less than 25 days to grow before bulbing is triggered at 14 hours of daylight on April 25th.

Even if it’s 15 hours (May 18th) that triggers that variety, seedlings would only have about 40 odd days to grow. That’s no where near enough. Bulbs would probably be dime size.

Does Transplanting Onion Seedlings Cause Bolting?

No. Transplanting seedlings does NOT cause bolting.

The normal life cycle of an onion is to grow, come to maturity, go dormant and after a period of cold resume growth and send up a seed stalk (bolting).

In short, bolting is caused by severe temperature swings that cause the onion to go dormant when it’s not suppose to.  That makes it prone to bolting.

Final Thoughts

The book I’m writing on onions will go into much more detail. It’s been slow going for lots of reasons, but I think it’ll be an even better book because of it. (And, yes, I know — it seems to be taking forever!)

I want to help you as much as I can. So, if you have problems with onions, let me know what they are.


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  • Theresa is the onion guru! I never had any success with onions from seed until I started the seeds in the little milk jug greenhouses as she does. I start mine the week of Christmas/New Years (Middle Tennessee, Zone 7) and keep them out on the porch unless we are having subfreezing weather until it’s warm enough to plant them in the garden.

  • PS: The Mako onion seed that one of your readers (Jack) shared with me germinated again this year!

  • Theresa,
    I’ve told you before…I’ve been an avid vegetable gardener for 45 years and could never grow onions to any size UNTIL I MET YOU. With your instruction, I now can grow very large onions that cure and store for winter, with the right variety up to 6 months! It was only possible with your help, that’s all I know. Can’t wait for your book!

  • I’m looking forward to that book Theresa

    I can relate to Toni’s confusion…those seed packet instructions may be correct for ” somewhere”, but for most are instructions for small bulbs (or failure). First instinct is to trust the writing on the packet but sounds like Toni’s experience saved her.

    For the average home gardener wanting to experiment and grow onions from seed for the first time, I’m sure those generic seed packet instructions have discouraged many to the point that they will only grow from sets or transplants, which is too bad!

    I learned it here years ago, that by choosing the correct type of onion based on location and understanding the life cycle and growing characteristics of onions, anyone, anywhere, can pretty much ensure success simply by learning the importance of timing which is based on latitude.

  • Onions ‘bolt’ for me (zone 6b) when I leave them in the ground over winter. I bought a bunch of plants and put them all around on the theory that they helped keep out moles and voles. Some died back in the late, dry summer and I missed them when I ‘went diggin’.
    Guess I wouldn’t make a smart squirrel either, HA.
    PS: I did have big one bolt and spend all summer making lots of good seeds for this year.
    Theresa, I really appreciate all the wisdom you share with us. Thanks

  • Thank you so much for this clarifying post.
    It is a rough work week for me so I will come back to this post at the end of the week and study it.

    I love that you share your wisdom with us.

  • Many states have a Master Gardener organization. And on their websites they typically list Recommended Varieties of veggies, fruits and flowers for their state or locale. I’ve found this to be very helpful. Here is a link for the state of IL for example: http://web.extension.illinois.edu/vegguide/step03.cfm Because I have shorter growing season here in Illinois, I prefer to start my onion seeds indoors in the beginning of January. And I transplant them in March or April after danger of frost has passed. I will definitely order your book. I welcome all the help I can get!!!

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