Gardening in Central Florida (USDA Hardiness Zones 9a and 9b) requires aligning the onion’s life cycle with the mild winter, avoiding the intense heat of late spring and summer. Onions are a cool-season crop that thrives under specific conditions. Careful planning and variety selection are necessary for a successful harvest. Understanding the precise timing and biological needs of the onion plant is the first step toward producing large, flavorful bulbs.
The Best Planting Window for Central Florida
The ideal time to plant onions in Central Florida is during the cooler months, specifically between October and December. This timing allows plants to establish robust top growth before the day length triggers bulbing. Planting sets or transplants is typically done in November, though starting seeds indoors can begin as early as September.
The goal is to ensure bulbs mature before the intense heat of late spring and early summer, which stresses the plants and affects final size and quality. Planting within this window allows the young onions to grow without the risk of premature bolting (flowering) and takes advantage of the short-day conditions necessary for proper bulb formation.
Selecting the Essential Short-Day Onion Varieties
Successful onion cultivation in Central Florida requires selecting a “short-day” variety. Onions are sensitive to photoperiodism, initiating bulb formation only when daylight hours reach a specific duration. Short-day onions begin bulbing when the day length reaches approximately 10 to 12 hours of light.
Central Florida’s latitude does not provide enough daylight hours to trigger bulbing in intermediate-day or long-day varieties. Choosing an incorrect variety results in the plant growing only green tops without forming a mature bulb. Recommended short-day cultivars for this region include:
- Granex (often sold as Vidalia)
- Red Creole
- Texas Early White
- Texas Grano
Proper Soil Preparation and Planting Depth
Onions require fertile, well-draining soil to produce large, healthy bulbs. Florida’s native sandy soil drains well but often lacks necessary organic matter and nutrients, making amendment mandatory. Incorporating organic materials like compost, well-rotted manure, or leaf mold improves soil structure and water retention. Onions prefer a slightly acidic to neutral soil pH, ideally ranging between 6.0 and 7.0.
When planting transplants or sets, place them about an inch deep into the prepared soil, ensuring the top of the bulb or the root-to-shoot transition is just barely covered. Planting deeper restricts bulb development, resulting in smaller onions. Space the transplants four to six inches apart to allow the bulb to swell, with rows separated by about a foot.
Maintenance and Knowing When to Harvest
Once planted, consistent maintenance encourages the rapid, healthy growth that leads to large bulbs. Onions have shallow root systems and cannot compete well with weeds, so the planting area must be kept weed-free. Consistent watering is also important, aiming for about one inch of water per week, as the sandy soil can dry out quickly.
Onions benefit from regular fertilization, particularly nitrogen, which fuels the top growth supporting the bulb. Apply a balanced fertilizer at planting and then side-dress with a nitrogen source every three to four weeks during the growing season.
The indicator that the crop is ready for harvest is a visual cue: the green tops will turn yellow and begin to fall over at the neck. This natural lodging signals that the plant is finished growing and is redirecting energy into the bulb. After gently pulling the onions from the soil, they should be cured in a dry, dark, and well-ventilated area for two to three weeks to dry the outer skins for storage.