Granex onions grown in my front-yard garden in Niceville. Photo by Dennis Gilson.
Granex onions harvested from my
front-yard garden in Niceville

How to grow ONIONS in north Florida

Onions grow well in north Florida vegetable gardens provided they are planted at the right time of the year and the correct variety is selected.

The right time of year to plant onion bulbs or transplants in north Florida is October to about mid November. If you are going to grow onions by seed, they should be started in early September in order to be ready for transplanting when the weather cools down in the fall. If you are going to start your onions from seed, buy fresh seeds each year because they do not store well.

If you are using store-bought transplants get them from a reliable dealer. Onion sets that have not been stored properly have a tendency to bolt early, which leads to lower yields.

While the suggested planting dates for onions in north Florida extends into December, onions planted that late in the year here are less likely to produce large, full-size onions. Wait even longer, say late January, and you may get large green onions instead of bulbs.

Onions are usually harvested in early May in north Florida.

In north Florida we typically grow selected varieties of “short-day” onions. Short-day onions require days that are only 11 to 12 hours long before plants switch from producing new foliage to growing bulbs. Suggested varieties of short-day onions for north Florida are Excel, Texas Grano, Granex, White Granex and Tropicana Red. Granex is the variety that is used for producing the popular Vidalia onions and St. Augustine Sweets. Texas Grano is an extra large, straw colored onion. Excel is a yellow onion and Tropicana Red is a red/purple onion.

Before planting, I usually mix some organic material into the soil, such as compost from the yard or composted cow manure from the garden center. A good rule of thumb is to dig a two-inch layer of compost into the soil to a depth of about six to eight inches. I also mix a balanced fertilizer into the soil, such as an 8-8-8 or 10-10-10, before setting out the transplants. I side dress the plants with fertilizer during the winter and in the spring when the bulbs are developing.

In north Florida gardens, onion plants are best spaced four to five inches apart in rows that are 12 to 24 inches apart.

Onions can be harvested as soon as the bulbs are large enough for your needs. They are fully mature when the tops of the plants turn from green to yellow and the foliage flops over to the ground. In north Florida this generally happens by mid May.

Once picked, cure the plants by allowing them to dry in an airy, dry place for about a week. Then clip the roots and tops, leaving about an inch of the dry neck. Sweet onions, such as Granex, are not long-keeping storage onions. The longer keepers, such as Texas Grano, will keep for several months.