Normal Onion Seedling Development and Indoor Care

Thread-thin, grass-like onion seedlings at 5 weeks are exactly right. Onions are slow starters—don't panic.

Indoor Seedling Protocol

• Light: Fluorescent/LED 3 inches above tips, 14–16 hours/day.
• Water: Consistently damp, not soggy. Bottom-water preferred.
• Fertilizer: None until 4–6 inches tall. Then half-strength liquid feed weekly.
• Trimming: If >5 inches, trim to 3 inches—prevents tangling, strengthens stems.

Transplant Timing

Hardened off, transplant 2–4 weeks before last frost. Onions tolerate light frost. Space 4–6 inches in rows 12 inches apart.

Seed Viability Check

Onion seed loses viability fast—1–2 years max. If germination <70%, buy fresh. Test: 10 seeds on damp paper towel, 70°F, 10–14 days.

Harvest Projection

Properly grown, spring-sown onions bulb in 90–110 days. In your zone, expect late August–September harvest.