Fall onions and photoperiod - Ask Extension
I have a "growth chamber" where I start seeds under grow lights. I am going to plant Walla Walla Sweets this fall. But am I messing them up ...
Knowledgebase
Fall onions and photoperiod #872291
Asked June 09, 2024, 1:27 PM EDT
I have a "growth chamber" where I start seeds under grow lights. I am going to plant Walla Walla Sweets this fall. But am I messing them up if I start them in the growth chamber with 24hour light? Or do I need to turn those lights off part of the time to replicate short days so they don't grow bulbs in the fall?
Thanks,
Steve, Corvallis
Benton County Oregon
Expert Response
Hi Steve,
Walla Walla onions are long day onions. They need 14-15 hours of daylight to bulb. You are right to start your seeds indoors to get the biggest onions possible. You want the biggest transplants possible to plant in August or September for larger, milder overwintered onions.
However, leaving the lights on 24 hours a day may trigger the onions to bulb. Most plants need a dark period to grow properly. You should consider limiting your lights to 15 hours. Watch the plants after they have germinated and see how fast they are growing. You might want to reduce the light period further if they grow too quickly.
I am attaching a publication from Utah University on growing onions. There are three videos within this publication with tips on growing onions in general.
If you have further questions, please contact us again.
Walla Walla onions are long day onions. They need 14-15 hours of daylight to bulb. You are right to start your seeds indoors to get the biggest onions possible. You want the biggest transplants possible to plant in August or September for larger, milder overwintered onions.
However, leaving the lights on 24 hours a day may trigger the onions to bulb. Most plants need a dark period to grow properly. You should consider limiting your lights to 15 hours. Watch the plants after they have germinated and see how fast they are growing. You might want to reduce the light period further if they grow too quickly.
I am attaching a publication from Utah University on growing onions. There are three videos within this publication with tips on growing onions in general.
If you have further questions, please contact us again.
Thank you, Sheryl. This helps a lot. I'll put a timer on my "growth chamber" where I germinate seeds and start plants.
Steve
Excellent idea. That way you will know just how long they are under the lights and can adjust the time if necessary. Have a great growing season Steve.
