Hardening seedlings is a crucial step in preparing them for transplantation into the open ground. This process allows plants to acclimatize to new environmental conditions, enhancing their resilience to temperature changes, wind, sun exposure, and other external factors. Neglecting proper hardening can result in stunted growth or even the death of seedlings.
When to Start Hardening
Begin hardening seedlings ideally 14-16 days before transplanting them into the soil. Cold-resistant crops like cabbage, lettuce, onion, and celery can start hardening at temperatures around +6-8°C, while heat-loving plants such as tomatoes, peppers, eggplants, cucumbers, zucchini, and squash should begin at temperatures around +12-14°C.
How to Properly Harden Seedlings
Gradual Increase in Outdoor Exposure:
- First 2-3 Days: Open windows in the room with seedlings for 2 hours.
- Following Days: Gradually increase outdoor exposure time to 6-8 hours daily.
- Two Days Before Planting: Allow seedlings to remain outdoors overnight.
Sun Protection:
- First 3-4 Days: Place seedlings in shaded areas.
- Subsequent Days: Gradually introduce seedlings to partial shade.
- End of Hardening: Seedlings can be exposed to direct sunlight.
Reducing Watering:
- First Week: Water seedlings as usual.
- Second Week: Reduce watering by half.
Nutrition:
- 5 Days Before Planting: Apply a universal mineral fertilizer if seedlings haven’t been fertilized since transplanting.
Important Considerations:
- Avoid hardening seedlings for more than 2 weeks to prevent growth retardation.
- Protect seedlings from night frosts by covering them with non-woven materials like spunbond, lutrasil, or agrofiber. Avoid using polyethylene film for shelter.
Hardening off seedlings is a straightforward yet critical process that ensures robust and resilient plant growth. By following these guidelines, you’ll successfully transition seedlings to the outdoors and nurture them towards a productive harvest.
