What's up with long day/short day onions?

Onion starting to flower

Saturday, February 13, 2016

There are 3 types of onions-short day, intermediate day, and long day onions.  Intermediate and long day varieties have been around for a long time.  Short day onions are relatively newcomers.  It is daylight hours in summer that determine which type is for you.

Onions are sensitive to daylight hours.  They start forming bulbs when daylight hours hit a minimum number of hours.  For long day onions, it is 15 hours.  For intermediate, it is 12-13 hours.  Short day onions are 9-10 hours.    In other words, until you have 15 hours of daylight, your long day onion will not form a bulb!

I would have thought long day onions would be for further south, but this is wrong.  The north get the really long summer days (think of Alaska in June with no darkness).  Long day onions should be planted in states north of the Oklahoma/Kansas border (approximately 36 degrees latitude).

Long day onions are planted in states in the northern part of the US.  Intermediate in the middle and short in the South.  

Short day onions are planted in the fall and form bulbs in the spring.  Intermediate and long day onions are typically planted in the spring as sets, not seeds.  Seeds require sprouting indoors and transplanting.  

In the Midwest, you start onions from seeds in early February.  Transplanting in March.  Transplanting should be done 4-6 weeks before the last spring freeze.  You can grow many more varieties if you start from seed, but plugs and sets of common varieties are readily available at nurseries and big box stores.

 You should enrich the soil with plenty of organic matter before planting.   As common sense would tell us, they also like loose soil.  Organic matter helps this along.  For more on growing onions, Onions-everything you need to know to grow 'em

Onions are ready to harvest when the tops turn yellow and fall over.  They should be pulled and allowed to harden in the shade for a couple of days before storing.