How to Grow Onions from Sets

Plant onion sets in early spring by pushing them into well-draining soil with the pointed end up, spacing them 4-6 inches apart in rows 12 inches apart.

1. Build the Perfect Onion Bed. Choose a sunny location with well-draining soil. Work the soil to 8-10 inches deep and mix in 2-3 inches of compost or aged manure. The soil should be loose and crumbly, not compacted. Test soil pH - onions prefer slightly acidic to neutral soil between 6.0-7.0.
2. Choose Quality Sets Only. Choose firm, healthy onion sets about the size of a dime or smaller. Larger sets tend to bolt and go to seed. Avoid any sets that feel soft, have green shoots longer than an inch, or show signs of mold or damage. Store sets in a cool, dry place until planting.
3. Get the Depth Just Right. Push each set into the soil pointed end up until just the tip shows above ground. Space sets 4-6 inches apart in rows 12 inches apart. Plant too deep and the onions won't form properly. Plant too shallow and they may push themselves out of the ground as they grow.
4. Lock in Moisture, Block Weeds. Water gently after planting to settle the soil around the sets. Apply a thin layer of straw or grass clipping mulch between rows to suppress weeds and retain moisture. Keep soil consistently moist but not waterlogged throughout the growing season.
5. Stop Bolting Before It Starts. Weed regularly by hand or shallow hoeing to avoid disturbing roots. Side-dress with nitrogen fertilizer when plants are 6 inches tall. Stop fertilizing 4 weeks before harvest. If flower stalks appear, cut them off immediately to encourage bulb development.
6. Time the Cure Just Right. Harvest when the green tops begin to yellow and fall over, typically 90-120 days after planting. Gently lift onions from soil and brush off dirt. Cure in a warm, dry, well-ventilated area for 2-3 weeks before storing.