Onion in Zone 8B — Southeast

Growing onions in the Southeast gives you the incredible satisfaction of pulling sweet, pungent bulbs from your own clay soil after months of patient tending. Our long 255-day growing season and reliable summer rain create excellent conditions for developing full-sized storage onions that beat anything you'll find at the grocery store. Whether you're making summer salsa with fresh tomatoes or storing braided onions for winter cooking, homegrown varieties offer superior flavor and the pride of complete self-sufficiency.

The hot, humid summers and afternoon thunderstorms can present some challenges with fungal diseases, but proper timing and variety selection make onions quite manageable in Zone 8B. Starting early in our moderate spring gives bulbs time to size up before the intense summer heat arrives, and the consistent moisture from our wet summers actually helps with bulb development when managed correctly.

Starting onion seeds indoors works well if you want the largest possible bulbs and don't mind the extra effort. You'll need to start seeds early to late December, about 10-12 weeks before your transplant date in late February through mid-March. This timing takes advantage of our moderate spring weather for strong establishment.

Set up seed trays in a warm spot (65-70°F) with good light once seedlings emerge. Bottom watering works best to prevent damping-off, which can be problematic in our humid conditions. The seedlings will look like thin grass and grow slowly through winter.

Keep in mind that onion sets (small bulbs) are much easier for beginners and still produce excellent results. Seeds give you more variety choices, but sets eliminate the indoor growing phase entirely and work just as well in our Southeast climate.

Transplant your indoor-started seedlings from late February through mid-March, when soil temperatures stay consistently above 40°F. This timing lets you take advantage of our moderate spring before the summer heat and humidity arrive. The plants can handle light frosts, so don't worry about those occasional temperature swings we get in early March.

Harden off seedlings gradually over a week, increasing their outdoor time daily. They'll need this adjustment period to handle our afternoon thunderstorms and variable spring weather. Plant them 4-6 inches apart in rows, setting them at the same depth they were growing indoors.

Choose a sunny spot with well-draining soil, which is especially important in our clay soil conditions. If you're working with heavy clay, consider raised beds or adding compost to improve drainage and prevent bulb rot during our wet summers.

Direct sowing onion seeds works well from early February through late July in the Southeast, though spring planting produces the largest bulbs. Soil temperature should be at least 40°F for germination, which happens reliably by early February in Zone 8B. Summer sowings work for green onions or smaller storage bulbs.

Prepare your planting area by working compost into clay soil to improve drainage and structure. Plant seeds ¼ inch deep and 4-6 inches apart, or broadcast thinly and thin later. Seeds germinate slowly, taking 2-3 weeks in cool spring soil.

Onion sets offer an easier alternative to seeds, especially for beginners. Plant sets in early spring, pointed end up, with just the tip showing above soil level. Sets establish quickly and give you a head start on bulb development before our summer heat arrives.

Onions need consistent moisture during bulb formation but can't tolerate waterlogged soil, which makes managing our wet summers crucial. Water deeply once or twice per week during dry spells, providing about 1 inch total including rainfall. Our average 45-55 inches of annual precipitation usually covers most needs, but you'll need to supplement during dry periods.

Use the finger test to check soil moisture 2 inches down before watering. In our clay soil, overwatering is often more problematic than underwatering since drainage can be poor. Water at soil level rather than overhead to reduce disease pressure in our humid conditions. Soaker hoses work particularly well for onion beds.

During summer, our afternoon thunderstorms often provide adequate moisture, but watch for signs of stress during hot, dry stretches. Yellowing outer leaves and slowed growth indicate water stress. Conversely, soft, rotting bulbs suggest too much moisture and poor drainage.

Stop watering entirely when tops begin to fall over and yellow in summer - this signals harvest time and the beginning of the natural curing process. A thin layer of straw mulch helps retain moisture and keep soil temperatures moderate during our hot summers, but avoid thick mulching that might promote fungal issues in humid conditions.

Your first onions will be ready from late May through late November, depending on variety and planting time. Spring-planted storage onions typically mature in mid-summer around 100 days from planting. The clearest harvest signal is when tops begin falling over and turning yellow - this happens naturally as bulbs reach maturity.

Pull bulbs when about half the tops have fallen over, choosing a dry day if possible. Brush off soil but don't wash them yet. The papery outer skins should be developing, and necks should feel firm. Small green onions can be harvested anytime for fresh use, but storage onions need full maturity.

After harvest, cure bulbs in a warm, dry, well-ventilated area for 2-3 weeks. A covered porch or garage works well in our humid climate. Proper curing develops the protective outer layers that allow long-term storage. Trim tops to 1 inch and roots to ¼ inch after curing.

With our first frost typically arriving in mid-November, you have plenty of time to cure and store your harvest properly. Well-cured onions from spring plantings can store through winter in a cool, dry place with good air circulation.

Onion Thrips These tiny insects create silvery streaks and stippling on onion leaves, eventually causing tips to turn brown and die back. The damage looks like tiny scratches or silver trails across the leaf surface. Thrips thrive in our hot, dry periods between thunderstorms and can quickly weaken plants, reducing bulb size.

Heavy infestations often occur during summer heat waves when beneficial insects are less active. Remove heavily damaged outer leaves and spray with insecticidal soap in early morning or evening. Blue sticky traps placed near plants help monitor and reduce populations. Maintaining consistent soil moisture and avoiding plant stress helps onions better withstand thrip damage.

Pink Root This fungal disease causes roots to turn pink, then purple, and finally black as they die back. Above ground, you'll see stunted growth, yellowing leaves, and smaller bulbs. The disease thrives in our warm, humid soil conditions and is particularly problematic in clay soil with poor drainage.

Pink root is soil-borne and spreads through contaminated tools, water, and infected plant material. Improve soil drainage by adding compost or creating raised beds. Rotate onions to a different area each year and avoid planting in spots where infected onions grew previously. Choose resistant varieties when possible and ensure good air circulation around plants.

Bolting Onion plants send up a tall flower stalk prematurely, causing leaves to become tough and bitter while the bulb stops developing. The plant shifts energy from bulb production to seed production, ruining your harvest. You'll see a thick, hollow stem emerging from the center with a round flower head forming at the top.

Bolting is triggered by temperature fluctuations, long days, or stress conditions - common during our variable spring weather or summer heat waves. Plant at appropriate times for your variety, provide consistent moisture, and choose bolt-resistant cultivars. If bolting occurs, cut the flower stalk immediately to redirect energy back to the bulb, though the onion should be used fresh rather than stored.

Southeast Specific Challenges Our combination of hot summers, high humidity, and clay soil creates perfect conditions for fungal diseases beyond pink root. Ensure good air circulation, avoid overhead watering during humid periods, and don't work in wet soil to prevent compacting clay around developing bulbs.

Onions make excellent companions for carrots, as their strong scent helps deter carrot rust flies while carrots' deep taproot doesn't compete with onions' shallow root system. Plant them together in alternating rows for natural pest control. Beets also work well alongside onions, sharing similar water and nutrient needs while their different root depths prevent competition in our clay soil.

Lettuce and other cool-season greens benefit from onions' pest-deterrent properties and can be interplanted for efficient space use during spring and fall. Tomatoes and onions are classic companions - the onions help repel aphids and other tomato pests while both crops thrive in our hot summers with consistent moisture. Avoid planting onions near beans or peas, as onions can inhibit their growth and nitrogen-fixing ability, which is especially problematic in our nutrient-demanding clay soils.