Onion in Zone 7B — Southeast

Growing onions in our Zone 7B Southeast climate gives you the satisfaction of harvesting sweet, storage-quality bulbs that far surpass anything from the grocery store. Our long growing season and reliable spring moisture create ideal conditions for developing those large, flavorful bulbs that make all the difference in your cooking. You'll find that homegrown onions store beautifully through our hot, humid summers when properly cured.

While our clay soil and disease pressure from humidity can challenge some crops, onions actually thrive in our conditions when planted at the right time. That generous 235-day growing season means you can start early and harvest late, giving your bulbs plenty of time to size up before our first frost in early November.

Starting onion seeds indoors makes sense if you want the largest possible bulbs or specific varieties not available as sets. You'll want to start seeds mid-December through early January, about 10 weeks before your transplant date in March. This early start takes advantage of our moderate spring conditions.

Set up seed trays in a warm spot around 65-70°F and provide good light once seedlings emerge. Bottom watering works particularly well for onion seedlings, keeping the soil evenly moist without encouraging fungal issues that our humid conditions can promote. The seedlings will look like thin grass shoots at first – perfectly normal.

Keep in mind that most Southeast gardeners find onion sets easier and more reliable than seed starting. But if you're after specific storage varieties or want bragging rights for the biggest bulbs, indoor seed starting gives you that edge.

Transplant your onion seedlings outdoors from early to late March, when soil temperatures have warmed but before our heat really kicks in. This timing takes advantage of our moderate spring weather and gives bulbs time to develop before summer stress hits.

Harden off seedlings gradually over a week, starting with a few hours of morning sun and building up their tolerance to outdoor conditions. Our March weather can swing between cool and warm, so watch the forecast and protect transplants if needed.

Space transplants 4-6 inches apart in rows, setting them at the same depth they were growing in their containers. Our clay soil benefits from working in some compost before planting, improving drainage around those developing bulbs. The roots need good air circulation to prevent rot in our humid conditions.

Direct sowing works well in our Southeast climate, especially with onion sets which are the most reliable method for beginners. Plant sets from mid-February through mid-July, though early spring plantings typically produce the largest bulbs.

Prepare your planting area by loosening our typical clay soil and working in organic matter to improve drainage. Sets should be planted pointed end up, barely covered with soil – just the tips showing. Seeds need consistent moisture and take longer to establish, making sets the preferred choice for most gardeners here.

Space both seeds and sets 4-6 inches apart in rows. Our spring rains usually provide adequate moisture for establishment, but you may need to supplement during dry spells. The key is consistent moisture without waterlogging, which our clay soil can promote if not properly amended.

Onions need consistent moisture during bulb formation but hate waterlogged conditions – a balancing act in our wet-summer climate with 45-55 inches of annual rainfall. During spring establishment, our regular afternoon thunderstorms usually provide adequate moisture, but monitor soil conditions closely.

Use the finger test: stick your finger 2 inches into the soil near the plants. If it's dry at that depth, it's time to water. Aim for about 1 inch per week, including rainfall. Our hot, humid summers mean you'll likely need to supplement natural precipitation during dry spells, especially in July and August when temperatures hit 92°F regularly.

Water at soil level rather than overhead to reduce fungal disease pressure in our humid conditions. A soaker hose or drip irrigation works perfectly. Stop watering completely when the tops begin to fall over and yellow – this signals the start of the curing process and too much moisture at this stage can cause bulb rot.

Mulching helps retain consistent moisture and keeps soil cooler during our hot summers, but keep mulch a few inches away from the bulbs themselves to prevent rot issues that our humidity can encourage.

Expect your first onion harvest from late May through mid-November, depending on when you planted and which varieties you chose. Spring-planted bulbs typically mature by midsummer, while succession plantings can extend your harvest well into fall before our first frost arrives.

The key harvest indicator is when the tops fall over and begin yellowing – usually about 100 days from planting. Don't wait too long after this happens, as our humid conditions can quickly lead to bulb rot if onions stay in wet soil. Pull the entire plant, roots and all, on a dry day if possible.

Brush off excess soil but don't wash the bulbs. Cure them in a warm, dry, well-ventilated area for 2-3 weeks until the outer skins are papery and the necks are completely dry. Our hot, humid summers make indoor curing essential – a garage with good air circulation works well. Properly cured onions will store for months in a cool, dry location.

As early November approaches and first frost threatens, harvest any remaining bulbs regardless of size. These late-harvest onions may not store as long but they'll still be perfect for immediate cooking through the winter months.

Onion Thrips These tiny, slender insects create silvery streaks and stippling on onion leaves, eventually causing tips to brown and die back. You'll see the damage before you spot the thrips themselves – they're about 1/16 inch long and pale yellow. Our hot, dry periods in July and August create perfect conditions for thrip populations to explode. Control them with beneficial insects like ladybugs, or use insecticidal soap sprays early in the morning before the heat builds. Row covers during peak season can prevent initial infestations.

Pink Root This fungal disease causes roots to turn pink, then dark red or purple, eventually rotting completely. Above ground, you'll notice stunted growth and yellowing leaves that look drought-stressed even when soil is moist. Our clay soil and humid conditions provide the perfect environment for this soil-borne fungus. Improve drainage by adding compost and avoid planting onions in the same spot year after year. Choose resistant varieties when possible, and ensure good air circulation around plants.

Bolting Premature flower stalk formation makes leaves bitter and stops bulb development – you'll see a thick, hollow stem shooting up from the center with a round flower head. Our temperature swings between cool nights and hot days, combined with drought stress during summer heat, commonly trigger bolting. Plant at the right time for your zone, provide consistent moisture during hot spells, and choose varieties suited to our climate. If bolting occurs, cut the flower stalk immediately to redirect energy back to the bulb.

Southeast Specific Challenges: Our combination of clay soil, humid conditions, and intense summer heat creates a perfect storm for fungal diseases and pest pressure. The key is improving soil drainage, providing consistent but not excessive moisture, and choosing varieties bred for hot, humid climates. Our long, wet summers mean disease prevention is always better than treatment.

Onions make excellent companions for carrots, beets, lettuce, and tomatoes in our Southeast gardens. Their strong scent helps deter many common pests, while their upright growth doesn't compete for space with these lower-growing crops. Carrots and onions are classic partners – the onions repel carrot flies while carrots help break up clay soil around onion bulbs. Lettuce benefits from the pest protection onions provide, especially important during our bug-heavy summers.

Avoid planting onions near beans and peas, as onions can inhibit the nitrogen-fixing bacteria that these legumes depend on. In our clay soil conditions, this relationship becomes even more problematic since beans and peas already struggle with our dense earth. Space these crops in separate areas of your garden to let each thrive in our challenging Southeast conditions.