Vidalia onions are sweet, mild granex-type onions commercially protected to specific counties in southern Georgia, where low-sulfur sandy loam soils suppress the compounds responsible for pungency in most onions. Home gardeners outside that region can grow the same granex hybrids or comparable sweet varieties; bulb flavor will vary with local soil chemistry, but the cultivation method is identical.
Onions are daylength-sensitive crops. Short-day types, including the granex varieties used for Vidalia production, begin bulbing at 10–12 hours of daylight and suit zones 7–9, where they are planted in fall and harvested the following late spring. In zones 6–7, set out transplants or sets 4–6 weeks before last frost using intermediate-day or long-day sweet types. Consistent nitrogen feeding through mid-season is the primary driver of bulb size; stop fertilizing once bulbs begin pushing out of the soil. Shallow, consistent irrigation matters more than volume — uneven watering causes splits and doubles. Sandy loam or well-worked loam drains fast enough to prevent the fungal rot diseases that plague onions in heavy soils.
Allium cepa contains quercetin and related flavonoids with documented anti-inflammatory and antioxidant properties. Traditional uses across many cultures include easing respiratory congestion, supporting cardiovascular function, and topical application for minor wound care. Antimicrobial activity is supported by laboratory evidence.
Onion White Rot
Yellowing and dieback of leaves, soft rotting at the base, and a fluffy white fungal growth with small black sclerotia on roots and lower stems.
Remove and destroy infected plants. Do not compost. Avoid replanting alliums in affected soil for several years and rotate crops. There is no chemical cure once established.
Downy mildew
Yellowing on top of leaves with grey-purple fuzz underneath. Spreads rapidly in humid conditions.
Remove affected leaves. Improve air circulation. Avoid overhead watering. Copper spray as preventive.
Botrytis (grey mould)
Grey fuzzy mould on petals and stems, worst in cool wet conditions.
Remove affected parts immediately. Improve air circulation. Avoid overhead watering. Apply copper fungicide if severe.
Fusarium wilt
Sudden wilting, brown streaks in stems, yellowing leaves. Affects sweet basil varieties most.
No cure. Remove and destroy plants. Do not replant in the same spot for 3+ years. Choose resistant varieties.
Bacterial Soft Rot
Rhizomes turn mushy and foul-smelling; foliage yellows and pulls away easily at the base. Often follows borer damage or overly wet soil.
Cut away all soft tissue back to firm rhizome, let it dry, and dust the cut with sulfur. Improve drainage and avoid burying rhizomes. Destroy badly infected plants.
Damping Off
Seedlings collapse at the soil line with thin, water-soaked stems; seeds may fail to emerge or rot before sprouting.
Sow in well-draining mix, avoid overwatering, and ensure good airflow. Remove affected seedlings and let the surface dry between waterings.
Fungal leaf spot
Brown or purplish spots on the leaves, often ringed with a yellow halo, that spread and merge in warm, humid, or wet weather; heavily spotted leaves yellow and drop early.
Pick off spotted leaves and clear fallen debris to remove overwintering spores. Improve air circulation by thinning, and water at the base so foliage dries quickly. If it persists, apply a copper- or sulfur-based fungicide at the first sign.
Pink Root
Roots turn pale pink shortly after infection, then progress to deep red, purple, and finally brown as they shrivel and die. Affected plants are stunted and may produce secondary roots that also become infected. Foliage yellows and plant vigor declines sharply.
Rotate alliums out of affected beds for a minimum of 3–4 years; the causal pathogen (Phoma terrestris) persists indefinitely in soil. Use certified disease-free transplants and sets. Maintain well-drained, fertile soil conditions — drought stress and waterlogging both increase susceptibility. No curative chemical treatment is reliably effective once infection is established.