Wednesday, June 1, 2016

Growing Onions in Warm Climates

I cook with onions almost daily, so I would like to have an abundance of them in my garden.  However, I have not been very successful growing onions.  I live in South Carolina (zone 7) and here it is recommended to plant onions in the fall and harvest in the spring.  When reading about onions, not all onions are the same.  There are long day, short day and neutral day (intermediate) onions.  Long day onions are best for northern climates (zone 6 and colder).  This is because the summer days are significantly longer than winter days in the north.  In the South, the day length between summer and winter doesn’t differ as much, so short day onions are best.  Day neutral onions should form bulbs in any zone. 

To understand all of this is helps to recap the biology of onions.  Onions are bulbs, which are modified fleshy leaves.  The layers of leaves that form the bulb grow based on nutrients and water.  They grow from the inside, pushing older layers outward.  The layers are consumed for calories during flowering and during drought, so the size of an onion and the number of layers can vary.  The outer layers keep dying as new layers grow internally and the bulb expands. 

Long day onions receive their cue to start bulbing when day length reaches 14 to 16 hours.  It doesn’t matter when onions are planted.  What matters is the amount of dark and light that an onion is exposed to determine when and if it will bulb, flower and set seed.  Short day onions need 10 to 13 hours.  If short day onions are grown at northern latitudes, then when the days reach 10 or more hours the onion will start forming a bulb.  The problem with this is that it will be early spring and the onion will be tiny.  The reason for planting onions in the fall in warmer climates is to get some vegetative growth before the day length trigger.  This will result in larger bulbs in the spring.  Based on all this information, short day onions are the best for my zone 7 garden.

Armed with all this information about onions, I set out to pick a short day onion that stores well.  My decision was the Red Creole onion.  Sow True Seeds describes it is as “a very large red onion perfect for the South.”  This had to be my onion, so I ordered seeds and planted them last fall.  Then I waited and waited.

Instead of onions I got flowers:

Some of the flowers are even producing little onion bulblets.

Pretty, but not what I was aiming for.

Getting the right day length isn’t a guarantee that I get to harvest onions.  Onions are biennials, meaning it should take two years to flower.  However, that is not always the case.  Onions can flower prematurely, called bolting.  This can happen when there is a cold snap and the onions go dormant.  As the temperatures increase, the onion starts growing again, but now it thinks it has been through two winters and will start taking resources from its bulb and produce a flower stalk and flower, which means the onion bulb does not grow anymore and can shrink.  Basically the onion plant thinks that its life is almost over and prepares to reproduce before dying.  I refer to our springs here as bipolar.  One day it is summer, the next day is winter.  I can understand how the onions could get confused.  The lesson I learned this year is that not only do I need short day onions, but I also need bolt resistant onions. 

It turns out that among the Red Creole seeds I planted last fall were a few White Castle onions as well and here they are bulbing nicely:

I think I may have found my onion variety! 

Of course, like any good gardener, I don't give up and here are spring planted Red Creole onions:

 Maybe if they didn't like fall planting they will do better in the spring.  I'm guessing I won't get very big onions, but that's alright.  Some small onions are better than no onions!


  1. I'm so glad that the White Castle onions seem to be working out well for you - onions can be a tricky crop, especially for those in southern latitudes it seems. But you have definitely hit on one of the best ways to find good varieties/methods for your garden - try them out for yourself! I think too many people give up too easily or don't even try certain methods, etc., simply because they "heard" that it wouldn't work.

  2. Good luck on your onion growing. I grow some in pots but they don't get real big. But like you say, small onions are better than no onions. I hope you are successful! Nancy

  3. Great post Julie. It seems you are getting your onions well and truly sorted out. Onions and leeks do have really cool flowers! Like you I use a ton of onions - red and white. There is an old proverb (I think in Spain) which says something like "You cannot even cook unless you have onions and garlic". I take their point. They are certainly both always in abundance in my kitchen. Love your blog.