Sun: Plant in full sun (6 to 8 hours). Space 2 to 4 inches apart within rows or 3 to 4 plants per 2- to 3-gallon container. Plant January through March and September through October.
Soil: Amend with organic matter to create a well-drained soil. Avoid planting in unamended sandy or heavy clay soils. If the soil test shows pH is below 6.2, apply lime in October or November as recommended.
For proper drainage in a container garden, use potting mix and ensure containers have drainage holes. Alternatively, consider using self-watering containers.
Water: Keep soil consistently moist but not saturated. Apply 1 to 2 inches of water each week. Avoid wetting leaves to prevent fungal disease. Mulch helps retain moisture.
Plant: Direct sow seeds 1⁄2 inch deep. Plant onion transplants (sets) 1⁄4 inch deep. For spring plantings, use sets instead of seeds. For large bulb onions, plant transplants at least 2 inches apart. If buying transplants, choose those with healthy color and a stocky appearance. Dig the planting hole as deep as the root ball or slightly deeper. Firmly pat down the soil and water deeply.
Fertilize: In the absence of a soil test, apply an all-purpose fertilizer (8-8-8 or 10-10-10) at planting, according to label directions. Reapply beside plants, 4 to 6 inches from the stem (side-dress), when tops are 6 inches tall.
When onion plants have about 5 leaves, side-dress with about 1⁄2 cup of 15-0-15 per each 10 feet of row.
Insects/Diseases/Weeds: Scout plants frequently for insect/disease damage. Use insecticidal soap (for soft-bodied insects) or Bt dust or spray (for caterpillars, or worms). Spray fungicide regularly to suppress common fungal diseases. Always follow label instructions. Mulch inhibits weeds and diseases.
Harvest: Harvest at 40 to 120 days. Harvest time varies depending on the variety.
Other: Green onions are ready when they are 6 to 8 inches tall. Bulb onions are ready for harvest when stems weaken and fall over. Pull them from the garden and place in a protected area to dry for 1 to 2 days. After drying, remove tops and roots and store in a dry, cool area.
Visit www.aces.edu/go/growmore for more information.
Learn how to grow the best fruits and vegetables with the Grow More Garden Series at www.aces.edu/go/growmore.
Bethany O’Rear, Regional Extension Agent, Home Grounds, Gardens, and Home Pests, Auburn University
Revised December 2023, Grow More Onions, ANR-2876-M