- Onion is a cool-season vegetable that can be grown successfully throughout most of temperate North America. Onions may be grown from sets, transplants or seeds.
- Onions start bulb formation when the day length is of the proper duration and different varieties of onions require different day lengths to initiate bulbing.
- In general, most common varieties fall into one of two classes, long-day (for northern latitudes) and short-day (for southern latitudes).
- Late plantings of the suggested varieties also result in small bulbs or lack of bulbing altogether in any location.
- High temperatures and low humidity are advantageous during bulbing and curing.
- Onions have shallow roots and compete poorly with weeds and grasses.
- Timely shallow hoeing and cultivation are important, especially when the onions are small.
- To produce green onions, plant the larger sets 1 _ inches deep and close enough to touch one another (green onions are harvested before crowding becomes a problem).
- To produce dry onions, plant the smaller sets 1 inch deep, with 2 to 4 inches between sets.
- Allow 12 to 18 inches between rows.
- If sets are 2 inches apart, harvest every other plant as green onions so that bulb development of the remaining sets is not impeded by neighboring plants.