Growing onions successfully in Florida presents a unique challenge, requiring a planting schedule that is the reverse of what most northern gardeners follow. Achieving a substantial bulb harvest depends entirely on selecting the correct variety and aligning planting with Florida’s short-day winter cycle. Onions are photoperiodic; the length of daylight hours triggers the switch from leaf growth to bulb formation. Understanding this biological necessity is the first step toward a successful harvest.
Optimal Planting Windows Across Florida Regions
Planting onions in Florida is dictated by the need to establish a large root and leaf system during the coolest part of the year. Unlike northern areas where onions are a spring crop, Florida gardeners plant in the fall and early winter to take advantage of milder temperatures. This schedule ensures the plants have sufficient vegetative growth before increasing daylight hours trigger bulbing in late winter and early spring.
The state’s distinct climate zones create a staggered planting window, with the northern region starting the earliest. North Florida gardeners can plant from late September through November, utilizing cooler temperatures that arrive sooner and last longer. This earlier start allows onions to size up before the heat returns.
In Central Florida, the ideal planting window shifts to October through early December, accommodating the delayed arrival of cool weather. South Florida, which experiences the mildest winters, plants latest, typically from late October through December. The goal across all regions is to avoid intense summer heat, which stresses the plants, and planting too late, which results in small bulbs.
Planting during the correct window allows the onion to maximize growth during the short-day period, ensuring the leaf development necessary for final bulb size. A general rule is that the larger the green top growth before bulbing begins, the larger the final harvested bulb will be. Harvest usually occurs four to five months after planting, typically in late spring before the intense summer heat begins.
Choosing the Right Onion Type for Success
Selecting the appropriate onion variety is the single most important decision for a Florida harvest. Onions are classified into three types based on the amount of daylight they require to initiate bulbing: long-day, intermediate-day, and short-day. Florida growers must exclusively choose short-day varieties because they only need 10 to 12 hours of daylight to transition from leaf growth to bulb formation.
Planting a long-day variety, which requires 14 to 16 hours of daylight, results in a plant that never receives the signal to bulb in southern latitudes. These varieties only produce green tops, failing to form a usable bulb. Short-day onions are adapted to the southern latitudes, initiating bulbing as the days begin to lengthen after the winter solstice.
Short-day varieties are typically sweeter and milder in flavor due to higher water and lower sulfur content. Reliable options include Granex, the cultivar behind the famous Vidalia onion, and the Red Creole or Red Burgundy types. Other proven options are Texas 1015 Supersweet and Texas Early White, all bred to thrive in the short-day conditions of the Southern United States.
Starting Onions: Seeds, Sets, or Transplants?
Onion cultivation can begin from seeds, sets, or bare-root transplants, but transplants are the most reliable method for the Florida home gardener. Transplants, often called “starts,” are small, pencil-sized, bare-root plants grown by a commercial nursery and shipped ready for immediate planting. They offer a significant advantage by skipping the lengthy and difficult seed germination phase.
Using transplants ensures the plant has a head start to achieve maximum leaf growth within the tight planting window. While starting from seed allows for the widest variety selection, it requires starting seeds indoors as early as September and two extra months of care before transplanting.
Onion sets, which are small, dormant bulbs from the previous season, are generally discouraged in Florida. The risk of the set bolting, or prematurely sending up a flower stalk, is higher in the warm southern climate. Bolting diverts energy from bulb growth and ruins the harvest.
Essential Care and Harvesting Guidelines
Once transplants are in the ground, consistent care is necessary to promote the large, healthy tops that lead to big bulbs. Onions have shallow root systems, making consistent moisture a requirement throughout the growing season. Gardeners should aim for moist, but not saturated, soil, which often means regular watering, especially during dry winter periods.
Fertilization should focus on vegetative growth during the initial stages. A balanced fertilizer applied at planting is a good start, followed by a nitrogen-heavy fertilizer every few weeks to encourage large, green tops.
Once the onion begins to form a bulb, usually in early spring, high-nitrogen feeding should stop. Too much nitrogen at this later stage promotes continued leaf growth at the expense of bulb enlargement.
Harvest is signaled visually when the green tops begin to yellow and fall over naturally, typically when about one-quarter of the tops have collapsed. The plants are then pulled from the soil and left to cure for two to three weeks in a protected, dry, and well-ventilated area, such as a garage or porch. This curing process allows the neck to dry completely, sealing the bulb and creating the papery outer skin necessary for extended storage.