27. March 2019

Growing early onion in the polytunnel

What could be better than getting a nice harvest of early onion from the polytunnel? I decided to go for a fast-growing variety and it seems to work!

En interiörbild från tunnelväxthuset, massa jord. Early onion, from inside the polytunnel.

This is what my polytunnel looked like before I planted the early onion in the bed to the left. It has been quite dry in here these past few months and I have been watering for a few days now to keep the soil moist.


I tried growing early onion in my large polytunnel a few years ago. It did not go well. Plenty of onion greens but no bulbs. I do like the greens too of course, but the whole point was getting early onion bulbs. I concluded that it must have been too hot which must have stressed the plant to go for leaves and flowers instead of a nice bulb.

I recently heard that two other growers here in Sweden, Sanna and Jonas Ringqvist from Bossgården, plant onions in their polytunnel in March. They have a small agricultural business and do a lot of experimenting in order to get both early and late vegetables that they can sell. Amongst many other things, they plant onion that they can start harvesting in May, already in March. When I did it last, I think I started too late. I should have gotten to it a bit sooner so that they didn't have to die of heat shock. I need to try it again!


Read more: Growing alliums from seed


En hand håller en liten lök, stor som en liten valnöt. Early onion, a hand holding an onion.

The onion set is very small, but it grows quickly and will develop normal-sized bulbs in a short amount of time.


Fast-growing yellow onion

I decided to go for the variety Forum F1 which the garden center I bought it from describes like this:

“Forum is the perfect choice for the eager gardener. It's one of the earliest fast-growing varieties out there. You can plant it early without having it bolt. The root system is quite shallow and you need a lot of nutrients and water. Forum produces nice, mild-tasting globe-shaped bulbs.

This description seems perfectly aligned with what I'm going for, early onion. Last year's harvest was sub-par to put it nicely, and I'm so eager to get really good homegrown onions.

If you are new to alliums, the part about bolting basically means that you can plant your onion set early in the year. Alliums (for example yellow onion, red onion, silver onion) will bolt very easily if they are exposed to very cold temperatures. This will stress the plant out. When the onion bolts, a hard core and stalk start to develop inside the bulb. This makes the onion taste bad.


More about alliums: Growing garlic in pots


En bädd sedd ovanifrån med en rad sättlök i mörk jord. Early onion, a bed from above.

I'm planting the onions 4 inches (10 centimeters) apart in a row, around 20 feet (6 meters) long.


The tunnel I'm planning on growing my onion in faces north and it's a bit colder in there than in my large polytunnel. It gets some light in the morning and afternoon. This might not be the optimal situation for onion, but I will give it a try.

The onion set is small and I plant it just below soil level, in a row with nice and airy soil. I cover the onions with row cover right after planting the sets. It's been pretty cold here at night, even below freezing at times. The weather report tells me it's going to be warmer the coming 10 days though, so I'm hoping for the best!


Read more: Tips for growing chives


Tunnelväxthuset med en vit fiberduk över jorden till vänster. Early onion, the polytunnel with row cover.

Use row cover when you want to grow early onion, this will help your alliums through the cold nights. I remove the row cover during the day so that the sun can warm the soil.


All I can do now is wait for my early onion! We will see what happens. It has been about two weeks since I planted the onion set, and the green leaves are finally starting to sprout. I can't wait!
/Sara Bäckmo

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