Seedling Care: Transplanting, Thinning, and Preventing Damping Off

When seedlings develop their second set of true leaves, it's time to transplant or thin.

Thinning

If you don't need many plants, thin in place: pinch/snip excess, leaving remaining seedlings ~2 inches apart. In individual pots/cells, thin to one plant per container.

Transplanting

To save most seedlings, transplant to larger containers (individual pots or cell-packs) to minimize root disturbance later. Fill new containers with moist mix. Loosen soil around seedlings (fork/spoon helps), lift carefully by leaves (not stems). Poke hole, place seedling, firm soil, water immediately. Keep out of direct sun a few days to recover.

Hardening Off

About 10 days before planting outside, stop fertilizing. Set seedlings outdoors several hours daily in a wind-sheltered, filtered-light spot. A cold frame is useful. Gradually increase exposure until in full sun all day (shade lovers excepted). Then plant in garden.

Damping Off Prevention

If seedlings collapse and die, fungal "damping off" may be the cause. Types: stem collapses at soil line, or seedling rots before emergence/seed decays.

Prevent by using pasteurized potting mix and new or thoroughly washed/disinfected containers. Consider fungicide-treated seeds. Avoid overwatering; ensure good air circulation and ventilation so tops stay dry. Thin seedlings to eliminate crowding.