How to Select the Best Onions and Leeks
The Long and Short Of It
The most important step in successfully growing onions is choosing a variety with the correct day length for your garden. Before you consider any other pros and cons of specific varieties, you’ll need to know which type of onion grows best in your area. This is based on sunlight and temperature. Leeks are not sunlight dependent, and can be grown in most zones.
Long-day onions need at least 14 hours of summer sunlight to bulb up, prefer cooler temperatures, and thus are suited for northern regions. These are usually planted in the spring and form a bulb over the summer. If planted in the south, they won’t get enough sunlight to form a good size bulb.
Short-day onions need 12 hours of sunlight to bulb up, and are best suited to the temperatures of southern regions. They are usually planted in the fall to over-winter. Bulb growth is triggered in the spring as the days lengthen, for a late spring or early summer harvest. If planted in the north, they will begin to bulb up early but stop short of reaching full size.
Intermediate-day onions, also called day-neutral onions, can be grown in almost any zone, but will not do well in south Florida or south Texas. They form bulbs at 12 to 14 hours of daylight. They can be planted like long-day or short-day onions, depending on how mild your winters are. For a map and more information on onion day lengths, read this post and watch our video.