Growing Onions In Cold Climates & The Subarctic

Onions are almost always on every gardener’s bucket list.

Onions are an extremely versatile vegetable in the kitchen that store well over winter, plus they have fantastic cold climate tolerance!  It’s a no brainer that it’s one of the most popular vegetables that gardeners want to grow!

It is also well known that onions cause many gardeners serious trouble!  Many experienced gardeners have sworn off growing them forever!

This subarctic focused growing guide will help guide you through the tricks, trials and tribulations of getting onions to maturity at subarctic latitudes!

Mind The Age Of Your Seeds

Onion seeds are one of those seeds that really don’t last all that long.  Even when properly cared for, the age of your seed stash matters!

Most sources out there recommend replacing pretty much all onion seeds every single year.  There is some wisdom to this.

We think that can seem a bit wasteful.  So we’ve studied onion seed viability in some depth ourselves.

You can try to “eek” a second, and sometimes even a third, year from your onion seeds.  Remember, seed viability doesn’t just “end” – you’ll simply see lesser and lesser numbers of seeds reliably germinate.

If you want to extend your seeds, you’ll want to overplant.  For year two, we generally recommend at least double what you actually need.  For year three, we’d recommend triple or even quadruple.  From here, you can select the best genetics to move forward with.

We have seen that after year three, seed viability can get really poor.  You can still get 4+ year old onion seed to germinate, but this is really the time we’d recommend replacing your seeds.

Use Onion Sets To Bypass Very Early Seeding Schedules

You will find that commercial greenhouses really don’t sell onion starts.  They simply aren’t economical to sell, since you can usually find an onion at your grocery for less than the cost it would take to make an onion start and turn a profit.  One start equals one onion.

The only way to do it at a commercial level is through very large scale.

Onion sets are available that can be direct sown in your soil, typically around last frost.  Onion sets are basically onions that have been grown from seed, but are “harvested” well before they become a full onion.  The green stems and roots are removed and the immature onion is allowed to cure, allowing for longer term storage.

These are onion sets, which can be purchased from many nurseries and seed houses.  They offer a gardener a way to “get ahead” where you basically are “finishing” the onion in your own garden.

Once planted again, the onion will spring to life.  Sort of like the experiment many of us have done “planting” a celery stump in a glass of water to re-grow the celery plant.  Since the onion is all ready a decent size, it’s far more practical to grow it in a single, summer season.

Onion sets are typically direct sown around last frost.  They are cold tolerant, so you can sometimes get away with sowing a week or two before if conditions permit.

The cons to onion sets are that they are much more expensive to buy compared to onion seeds.  While they are cheaper than grocery bought onions, the “is it worth it?” scale does tilt by quite a bit.

Also, we’ve grown them both ways, even side by side.  There’s a reason we grow our own onion starts.  Beyond being cheap, the “disruption” in the plant’s lifecycle does come at a cost to the final product.  Home grown onion starts are simply bigger, healthier and more vigorous than onions grown from sets.

Be Prepared To Defend At All Costs

Onions have an arch nemesis.  A source of pure evil that seeks only to prey on your hard work and take every single onion away from you.

There’s this dastardly creature called an onion fly.  It somehow survives -50F winters and can devastate an onion crop before you even know you have a problem.

A quick primer on the onion fly life cycle:

• Fly lays its larvae around a growing onion’s stem.
• The larvae then burrow into the soil.  The larvae eventually grow into full sized maggots.
• These maggots proceed to feast on your onions.  Your onion plant will eventually die and your onion will be un-storable and unusable.
• The maggot becomes a fly through pupation once it “grows up.”  It then flies off into the world to find and destroy more onions.

They are basically a butterfly from hell.  At least if you’re an onion.

We have navigated an onion fly infestation and beat them, but it wasn’t easy.  Many internet sources say you’re basically never going to grow onions again or you’ll have to move 5 miles away.  We proved that’s not true!

The very, very best thing an onion gardener can do is prevent an infestation.  Since these creatures are alive and well, despite our harsh winters, protection of your onion crop is essential.

We recommend covering all onions with a netting designed to keep flies and other bugs out.

We use PVC hoops on our raised beds, covered in a cloth-like bug netting, to help prevent the flies from gaining access to our onions to begin with.  This effectively disrupts their hunt for good larvae-laying grounds and they’ll fly on to find other, easier targets.

This is one of our protected onion beds.  We plant everything that is sensitive to onion flies (onions, shallots, garlic) under this type of netting.  This is very basic 1/2 inch PVC, secured with electrical conduit clamps.  We hold the cloth to the hoops with cheap clamps.

You can be dumb like we were and eventually lose an entire crop to the onion fly.  Or, you can be prepared, as we now always must be.  If we want to grow onions, anyway.

Bonus tip.  With the above kind of setup, you can also use frost cloth (also called remay cloth) to protect your onions (or other crops you might grow in raised beds) from unexpected frosts like so:

Plant Onions Densely, If You Can

Onions are one of those plants that can handle dense planting quite well.  Just like how they don’t get all intrusive when raised indoors, they live their entire life unobtrusively to other plants around it.

A farmer might plant rows upon rows upon rows of onions.  That’s not how we do it.

We use our raised beds to grow a thick batch of onions, all evenly spaced from one another.  The spacing allows for the bulbs to grow to full size with little interference from its neighbors in any direction.

This is one of our onion beds shortly before harvest.  We know the onions are “done” because the stems have laid down to the ground.

For the spacing, we borrow directly from the “square foot gardening” method.  This technique calls for onions to be sowed four per square foot.  This offers each onion about six inches of growing space in all directions.

In our experience, this works really well and allows a good bit of density in a small amount of space.  We usually dedicate about 20-25 square feet to our onion crop, which nets us a respectable 80-100 onions at harvest.

Again, because we insist on protecting our onions, we’re a bit less concerned about growing them using this density.

Grow Onions With Other Root Vegetables

Almost everything we discuss in this post is applicable to other root vegetables as well.  From fertilization to soil types, you’ll find a lot of similarity between them.

For this reason, it’s good to grow your onions with other root vegetables.  This allows you to treat larger areas in a similar way.

A couple of really good choices to combine with onions are beets and carrots.  Both of these are excellent companion vegetables.

Here you can see that we plant our onions with leeks, green onions and also carrots.  These are excellent companion plants and also are “compatible” with each other for many reasons.

We do think it’s a good idea to avoid interplanting with things like garlic.  Due to the problems with onion flies, which can also affect garlic, we prefer to keep these two separate to reduce risk.  If given the choice, we’d rather lose one or the other, but not both.

Some people strongly prefer to plant onions “wherever” in their garden and that can directly help avoid some problems with onion flies.  It’s not a “great” prevention technique in our opinion, though.  Concentrating your onions allows you to protect them all with other techniques.

You Too Can Grow Many Onions!

We hope that this article gives you a little insight into how we grow our own onions.  It’s been a learning process even for us, they are definitely not the easiest of things to grow!

Once you can provide protection of your onion crops, they’re really a blessing to have in the garden.  We love having our onions well into the following year, it’s been worthwhile for us.

If you’ve sworn them off forever, maybe you’ll reconsider it.  We won’t blame you if you don’t, too…onions are “cheap enough” to buy that some just won’t find it worth the hassle.

Lastly, everything we’ve mentioned in this article is also applicable shallots.  These are a culinary delight, but be aware these are a “favorite” of onion flies.  If you grow shallots too, it can increase your risk of an onion fly infestation.  Much of what we mention is also applicable to garlic and leeks, too, though we have separate guides for this as well.

Thanks for reading!