Your seeds germinated. Tiny green shoots appeared. Then, within 48 hours, they flopped over and died.
This isn't bad luck. It's damping off—and it's completely preventable.
The Collapse Point: Days 3-10
Most seedling death happens in a narrow window: after germination, before true leaves. This is when the loop collapses for 80% of first-time seed starters.
Why this phase is deadly:
- Seedlings have no immune system yet
- Soil surface stays wet (fungal paradise)
- Growers overwater from anxiety ("they look dry!")
Mistake #1: Starting Seeds Too Deep
Rule: Plant seeds at depth = 2x seed diameter. A tomato seed (2mm) goes 4mm deep. A bean (10mm) goes 20mm deep.
Too deep = seedling exhausts energy reaching surface = weak stem = damping off.
The fix: Use your pinky fingernail as a depth guide for small seeds. Press lightly, drop seed, cover with thin soil layer.
Mistake #2: Watering from Above
Overhead watering keeps soil surface wet 24/7. Fungal spores (always present in soil) activate and attack seedling stems at soil line.
The fix: Bottom watering. Set containers in a tray of water for 10-15 minutes. Soil wicks moisture up, surface stays drier, fungus stays dormant.
Do this until seedlings have 2-4 true leaves (not the initial cotyledon leaves).
Mistake #3: No Air Movement
Stagnant air = high humidity at soil surface = fungal growth. This is why greenhouse seedlings survive but your windowsill ones don't.
The fix: Gentle air circulation. A small fan on low, 6 feet away, running 4-6 hours daily. Not pointed at seedlings—just moving air in the room.
Bonus: Air movement strengthens stems (mimics wind).
Mistake #4: Keeping the Humidity Dome Too Long
Humidity domes boost germination rates. But once seeds sprout, the dome becomes a death trap.
The trigger: Remove dome when 50%+ of seeds have germinated. Gradually increase air exposure over 2-3 days (crack lid, then remove).
Keeping it on "just to be safe" creates the exact conditions that kill seedlings.
Mistake #5: Wrong Light Timing
Seedlings need 12-16 hours of light daily. Less = leggy stems = weak plants = collapse when you transplant.
But here's what nobody mentions: Light intensity matters more than duration.
A bright south window (6 hours direct sun) beats a grow light 3 feet away (16 hours). Proximity = intensity.
The fix: Place seedlings as close to light source as possible without heat stress. For grow lights: 4-6 inches above seedlings. For windows: directly on sill, not 2 feet back on a table.
The Damping Off Reset
If you've already lost seedlings to damping off, here's how to prevent it next time:
- Use fresh seed starting mix (not garden soil or old potting mix)
- Water from bottom only until true leaves appear
- Remove humidity dome within 24 hours of germination
- Add gentle air circulation from day one
- Reduce watering frequency by 30% (soil should dry slightly between waterings)
The Species That Forgive These Mistakes
If you're rebuilding confidence after seedling failure, start with high-forgiveness crops:
Lettuce/Arugula: Germinates in 3-5 days, tolerates cooler temps, shows problems early (you can course-correct)
Basil: Fast growth, clear watering signals (wilts when dry, perks up fast), hard to overwater
Tomatoes: Resilient once past day 10, recovers from minor mistakes, gives clear feedback
Avoid starting with: Peppers (slow + picky), carrots (finicky germination), celery (needs constant moisture).
The 10-Day Milestone
If your seedlings survive 10 days post-germination with strong stems and green leaves, success rate jumps to 90%+.
The goal isn't perfect germination rates. It's a system that gets seedlings past the danger zone without requiring hourly monitoring.
That's the loop that survives when life gets busy.
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