Thinking about growing onions but not sure which variety to choose?
There are three types of onions grown for bulbs. They are short-day, intermediate-day, and long-day onions.
The type gives us an idea on the amount of daylight needed for the onion to start producing its bulb.
Short-day varieties start producing their bulbs when they receive between 10 and 12 hours of daylight. Intermediate-day varieties need between 12 and 14 hours of daylight. And long-day varieties need between 14 and 16 hours of daylight to start growing their bulbs.
So how does one figure out the amount of daylight they receive?
We’ll make it simple!
We know our days are either getting longer or shorter, depending on what part of the year we are in. In the northern hemisphere the days start getting longer around the 21st of December. Each day thereafter receives more daylight until around June 21, which is the longest day of the year. Because the northern hemisphere is tilting towards the sun during the winter months, the furthest northern states actually receive more daylight than southern states.
Because the states to the south receive the fewest hours of daylight during the growing season, they should plant short-day varieties. If they try growing a long-day instead, it would never produce a bulb because it won’t receive the necessary hours of daylight to “switch on” its bulb production.
Because they receive the most daylight during the growing season, northern states should plant long-day varieties. If they try growing a short-day variety, it would receive too much daylight before its leaf growth had finished, resulting in a very small bulb.
The states in between should grow the intermediate-day varieties. Depending on which mid-states, some short- or long-day varieties might grow well, too.
For complete onion growing instructions, read; How to Grow the Most Flavorful Onions