Onion in Zone 10B — Florida

Onions are one of the most rewarding crops you can grow in Zone 10B Florida, offering incredible flavor that puts store-bought bulbs to shame. Here in our subtropical climate, you'll get sweet, mild onions that store beautifully through our hot summers, and there's nothing quite like pulling your own fresh green onions throughout the growing season. The satisfaction of braiding your own onion harvest while your neighbors are paying premium prices for imported bulbs makes this crop absolutely worth the garden space.

Growing onions in Florida does require working with our unique reversed seasons and managing our intense summer humidity, but the timing is actually quite forgiving. With our 360-day growing season, you have flexibility to plant in fall and harvest before the brutal summer heat sets in, or even grow them as a winter crop when most of the country is buried in snow.

Starting onion seeds indoors makes sense if you want the largest possible bulbs or specific varieties that aren't available as sets. Sow your seeds in early to late October, about 10 weeks before you plan to transplant them outside in late December. This timing lets you take advantage of our mild winter weather for the crucial bulb development phase.

Set up your seed trays in a warm spot with good air circulation - important here in Florida where humidity can cause damping-off issues. Use bottom watering to keep seedlings healthy and prevent fungal problems that our climate encourages. Your seedlings will need 12-14 hours of light daily, which can be challenging during our shorter winter days.

Keep in mind that onion seedlings grow slowly at first, looking like thin grass shoots for weeks. This is normal, and the slow indoor start actually works well with our reversed Florida growing calendar since you're not fighting our spring heat surge that comes earlier than most regions.

Transplant your onion seedlings outdoors during late December through mid-January when nighttime temperatures consistently stay above the mid-40s. This timing puts them in the ground during our coolest months, giving them time to establish strong root systems before our spring heat arrives in March.

Harden off your seedlings gradually over a week, starting with just 2-3 hours of morning sun and gradually increasing their outdoor exposure. Space transplants 4-6 inches apart in rows, planting them at the same depth they were growing indoors - don't bury the bulb formation area.

Watch for those occasional cold snaps we get in January and February. While onions can handle frost, protecting young transplants with row cover during unexpected freezes will keep them growing steadily. The key is getting them established before our intense spring sun and humidity kick in.

Direct sowing onion seeds works well in Florida, especially if you're growing them primarily for green onions or don't mind smaller bulbs. Sow seeds from early December through early September, though the December through February window gives you the best results for bulb formation.

Plant seeds about half an inch deep in well-draining soil - crucial in our sandy conditions where water can either drain too quickly or pool during our wet season. Space seeds 4-6 inches apart, or plant closer and thin later if you want some green onions for the kitchen while the others develop bulbs.

The easier route for most Florida gardeners is planting onion sets (small bulbs) instead of seeds. Sets establish faster, are more reliable in our humid conditions, and give you a head start on the growing season. Plant sets pointed-end up, just deep enough that the tip shows above soil level.

Onions need consistent moisture during their long growing season, but our Florida climate requires a careful balancing act. During fall and winter when they're establishing, water deeply when the top 2 inches of soil feel dry - usually every 3-4 days depending on our winter rainfall patterns. Our sandy soils drain quickly, so you'll need to water more frequently than gardeners in heavier soil regions.

As spring arrives and temperatures climb into the 80s, increase watering to maintain steady soil moisture without creating soggy conditions. Onions particularly need consistent water during March through May when bulbs are actively forming. During this period, aim for about an inch of water per week, including rainfall.

Water at the base of plants rather than overhead to reduce fungal disease problems in our high humidity. Our wet summers bring 50-65 inches of annual rainfall, but it often comes in heavy downpours followed by dry spells. Monitor soil moisture with the finger test - stick your finger 2 inches into the soil and water when it feels dry at that depth.

Stop watering entirely when onion tops begin falling over and yellowing in late spring or early summer. This signals the start of the curing process, and continued watering will delay proper bulb formation and storage quality. A thin layer of organic mulch helps moderate soil moisture and temperature during our intense summer heat.

Your first onions will be ready for harvest anywhere from mid-March through early January, depending on when you planted and which varieties you chose. The key indicator is when the green tops naturally begin falling over and turning yellow - this usually happens about 100 days after transplanting or 120 days from direct seeding.

Don't wait for all the tops to fall over completely. When about 50-75% of your onion tops have fallen and started yellowing, it's time to harvest the entire crop. Pull them on a dry day if possible, gently loosening the soil around bulbs with a fork if our clay-sand mix has hardened around them.

After harvesting, brush off excess soil but don't wash the bulbs. Cure them in a warm, dry, well-ventilated area for 2-3 weeks - your garage or covered porch works well during our dry spring weather. Proper curing is crucial for long-term storage, especially important here where you want onions to last through the summer when you can't grow them.

Since we rarely get hard frost until late December, you have flexibility with harvest timing. However, don't leave onions in the ground too long after tops fall over, as our summer humidity and occasional heavy rains can cause bulbs to rot or start growing again.

Onion Thrips These tiny, slender insects cause silvery streaks and stippling on onion leaves, eventually leading to yellowing and reduced bulb size. You'll see the damage as fine, pale lines running lengthwise on the foliage, and heavily infested plants may have a bleached appearance. Our hot, dry spring weather creates perfect conditions for thrips populations to explode, especially during March through May when onions are trying to bulk up.

Thrips thrive in our spring heat and can quickly overwhelm plants if not managed early. Use reflective mulch around plants to confuse thrips, and spray plants with water in early morning to knock them off. For severe infestations, beneficial insects like minute pirate bugs help, or apply insecticidal soap every few days until populations drop.

Pink Root This fungal disease turns onion roots pink, then purple, and finally black as they rot away, stunting plant growth and reducing bulb size significantly. You'll notice plants looking weak and yellowish despite adequate water and fertilizer, and pulling up a plant reveals the telltale pink-colored roots instead of healthy white ones. Our warm, moist soil conditions during fall planting season create ideal conditions for this soilborne fungus.

Pink root persists in soil for years and is especially problematic in our sandy soils that stay warm longer into winter. Plant resistant varieties when available, rotate onions to different garden areas each year, and improve soil drainage with organic matter. Once infected, there's no cure - focus on prevention and remove affected plants to prevent spread.

Bolting Onion plants that bolt send up tall flower stalks prematurely, shifting energy from bulb development to seed production and leaving you with small, tough bulbs. The leaves become bitter and the bulb stops growing, essentially ending your harvest early. This typically happens when plants experience temperature swings or stress during our unpredictable spring weather patterns.

Bolting is often triggered by planting too early and exposing young plants to cool temperatures followed by warm spells, or by inconsistent watering during our dry spring months. Choose varieties suited for your planting window, maintain consistent soil moisture, and avoid planting onion sets that are larger than a dime (bigger sets are more prone to bolting).

Florida Specific Challenges: Our extreme humidity creates perfect conditions for fungal diseases, while our sandy soils require more frequent watering and fertilizing than other regions. The combination of hot springs and wet summers means timing is everything - plant too late and summer heat prevents proper bulb formation, but plant too early and temperature fluctuations cause bolting problems.

Onions make excellent companion plants in Florida gardens, particularly with carrots and beets since their shallow root systems don't compete with onion bulbs developing underground. The strong scent of onions helps repel carrot flies and other pests that target root vegetables, while the different rooting depths make efficient use of your garden space. Lettuce also pairs well with onions during our cool season, as both thrive in the same temperature range and the lettuce provides living mulch that helps retain soil moisture in our sandy conditions.

Plant onions near your tomato transplants when you set them out in March - the onions will be nearly mature by the time tomatoes need the space, and onions help deter aphids and other soft-bodied insects that plague tomatoes in our humid climate. Avoid planting onions near beans or peas, as these nitrogen-fixing legumes can cause onions to produce more foliage at the expense of bulb development, and the different watering needs can create management challenges during our variable spring rainfall patterns.