Growing onions

Although onions can be grown from seeds, sets, or transplants, I prefer to grow them from seeds. After a cold winter, the arrival of seed catalogs and the starting of onions seeds remind me that spring is around the corner. I like to watch the seeds germinate and sprout long leaves which need to be cut 2-3 times before transplanting. I also like detangling the roots of the seedlings when it is time to transplant them in the spring. To me, onions = spring.

As an experiment, I planted Walla Walla onion seedlings last November. I read that planting sweet onions in the fall results in a sweeter onion. What I did not know was that the onions would be larger and mature much earlier than those planted in the spring. So, this November I will be planting even more onions to overwinter!

While I am already enjoying the Walla Walla onions (over 1 lb each!) I planted last fall, I have noticed that the onions I planted this spring are starting to bulb up nicely. I anticipate the rest of the onions being ready to harvest around the end of July.

Onion showing symptoms
of Pantoea ananatis

This week, I came across one sweet onion (Candy) that had suddenly looked kind of weird. The onion was bulbing up like the others, but it had floppy white/bleached looking center leaves (the outer leaves were green and healthy looking). Having seen what happens to tomato plants if disease is not controlled early, I ripped this onion out of the ground and started my investigation into what was the cause of the wilt. 

It turns out that the onion was likely infected with a bacterial disease caused by Pantoea ananatis. This bacterium causes what is called "center rot" and commonly occurs in sweet onions during periods of hot weather. The classical sign of infection is the collapsed bleached center leaves hanging down beside the onion's neck. Bingo! This is exactly what was wrong with my onion.

Go figure: high temperatures are necessary for the development of this disease. We have been in a 90-degree heat wave for about 2 weeks. This is another benefit of growing onions over the winter - they mature earlier, thereby helping to prevent loss from center rot.

I also suspect that the overhead misters I installed on the onion bed may have contributed to the bacterial disease. Water from the misters could be held in the leaf axils making the onion more susceptible to bacteria entering the plant. Needless to say, I have turned off the misters and will rely solely on drip emitters for the rest of the season.