Growing Onions – Top 3 Guidelines for Success

There are various reasons why some gardeners don’t succeed at growing onions. In the new book I’m writing on how to grow onions, I’ll tell ALL my secrets for being successful at growing onions and give the various reasons why many gardeners are unsuccessful.

But before this years growing season gets into full swing, I want to share at least the top 3 things that most often cause a gardener’s onion crop to be less than what they had hoped for.

As You Read, Keep This Mind

It won’t matter if you follow every guideline there is for onions or any other vegetable, IF you have not replenished your soil with organic material and fed the soil web (soil life). If that’s the case, you probably won’t be 100% happy with your onions. It’ll also be unlikely that you’ll have nutrient dense onions.

Soil is where success in growing ANY vegetable starts. Soil (not fertilizers) is always first and foremost for success in gardening that produces the most healthful foods.

What if Your Garden is New?

If your garden is new, plant anyway. The lessons learned while improving you soil will be invaluable.

(I’ve listed two posts at the end of this post that you may want to review that go into that very thing.)

Here are the 3 guidelines that gardeners most often overlook when trying to grow onions.

#1 Proper Time to Plant

Onions for warmer areas are usually planted in the fall.

For colder areas, onions are planted in the spring. A good rule of thumb for planting onion transplants to the garden is 6 to 8 weeks before the average last frost date.

Sometimes I plant even earlier. If you’ve read all my posts on onions you know that I like to put my transplants in the garden in late February or the first of March. That gives them time to grow enough leaves to make nice sized onions before daylight hours trigger bulbing. (The less the number of leaves, the smaller the onion will be.)

If you’re growing your onions from seed, start your seed about 6 to 8 weeks before you plan to transplant the seedlings into the garden.

You’ll still have a bit of cold weather when the onions go in, but they’re pretty hardy. I’ve had years when the temperatures fell below 20 degrees after planting. That’s not ideal, but they seemed to do ok anyway. Fortunately, those temperatures didn’t last long.

#2 Planting Depth

Whether you’re planting sets or transplants, plant your onions about one inch deep. If you plant much deeper, the onions won’t bulb and you’ll get a straight stalk.

(Onion sets are small onion bulbs produced from seeds the previous year.)

(Transplants are the seedlings started from seed for this growing season.)

Tip: Many times onions that have been too deeply planted won’t come up at all. BUT, they sometimes rise to the top naturally during the growing season and come up in the fall as spring onions.

#3 Plant the Correct Onion for Your Area

Getting the right type of onions for your area is important if you want good-sized onions.

Envision an imaginary line between San Francisco and Washington, DC.

Long Day Onions

Most gardeners north of that line would grow long- day onions since summer days are longer in the north. The long-day onions will continue to grow leaves until 14 to 15 hours of daylight triggers bulbing.

(It is said that if you grow short-day onions in the north, they’ll bulb too early to produce good-sized bulbs.)

Short Day Onions

Those south of that line would grow short-day onions, where only 12 hours of daylight is required to trigger bulbing.

(If you grow long-day onions in the south, they won’t bulb because they won’t get enough daylight hours to trigger bulbing.)

Intermediate Varieties

There are also intermediate varieties that are suitable for growing in the mid-section of the country. These onions start bulbing when the number of daylight hours reach 13 or 15.

How to know

Some seed suppliers don’t mention whether their onion offerings are long day or short day varieties. If you don’t see some indication of whether they’re short day or long day (sometimes indicated as S or L), do a Google search. Find out for sure rather than order the wrong onion variety and be disappointed.

If you happen to be one who buys from the local seed supply store, they’ll have onions that are the right day length for the area they’re in.

Here in Virginia I do well with almost any day length.

Final Thoughts

If you’re new to onions and/or don’t yet follow these guidelines, apply them this growing season. I think you might be amazed at the difference it’ll make in your onion crop.

And if you’re really into learning more about having the best onions ever, keep an eye out for my new book (or possibly an ebook?), where among other things I’ll go through more guidelines for success, how to have onions from the garden 12 months a year, reasons onions bolt, what you can do to prevent it, and much much more. I’ll keep you updated.

Related Posts:

Should You Wait Until Your Soil is Improved to Plant?

Organic Gardening – Think you Can’t Start This Year?

Onion Sets What You Need to Know to Get Better Results

Onions – Seed, Sets, and Transplants

All content including photos is copyright by TendingMyGarden.com.  All Rights Reserved.


  • I certainly appreciate your articles about onions and look forward to your book. Gardening started for me at birth – my parents grew and preserved most of our food supply. I`m old. Smile. Back to onions – you have given me so much new knowledge. Thank you so much.

  • I am so excited to see your new book. I am so very glad you prompted me to grow onions last year! Because of you I was successful and they truly were delicious. I think it was your last post (or a backlog?) where you explained what to do with any seedlings that you don’t have room to plant. Just dry them and use them as sets for next season. How clever!

  • Judeen, I loved how you put that: “gardening started for me at birth—”
    Wouldn’t it be wonderful if we could all say that!
    Glad you have benefited from my writings. And thank you for letting me know!

    Farming Bear and Sandra – As slow as I’m progressing on it, it may take some time to get it ready, but I’m headed in that direction. Thanks for the encouragement and for being excited about it!

    Toni, thank you too for being excited about the book. Thrilled to hear you were successful with onions last year! There is nothing like a sweet onion straight from the garden!

    By the way, Toni, I think regarding “what to do with any seedlings that you don’t have room to plant. Just dry them and use them as sets” —-to clarify one plants the seedlings close together. They’ll form small bulbs (sets). Then dry them and use as sets next season.


  • Oh I see, you actually plant the seedlings from your winter sown seeds into the garden. Planting them close together keeps them small enough that at end of season they will be small or tiny bulbs that you dry and plant again next season. Do I have that correct?

  • You have totally changed the way I look at my property! Instead of thinking about what to do with trimmed bushes and piles of leaves, I see mulch!

  • I grow long day onions, shallots, and green onions every year. I’ve never had problems and get the greatest big onions and huge shallots. Last year I was away a lot and wanted to keep weeds down. I usually use one inch of straw, but the straw we get around here has lots of seeds which germinate and overpower the garden if I’m not around to tend it. So I decided to try ground up leaves instead. BIG mistake. It kept the weeds out but devastated the onions. They had plenty of leaves but very few bulbs. No shallots at all.

  • JL, this is an interesting observation. Thanks for posting.
    I’ve planted onions for years with leaves and never had a problem.
    May be another variable?
    The only thing that comes to mind is that if the onions were buried into the shredded leaves too deeply, it could have caused them not to bulb.

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