What signs indicate seedlings are ready for transplanting?
Written by
Julia Anderson
Reviewed by
Prof. Charles Hartman, Ph.D.Harden off seedlings until they present obvious signs that they are ready to be fully outdoors. My tomato starts provided me with this lesson. They began leggy and pale, and once we successfully hardened them off, they became strong, woody-stemmed plants. I advise looking for three signs that you observe before you permanently take your plants outside.
Stem & Leaf Changes
- Sturdy stems resist bending when gently shaken
- Darker green leaves indicate thickened cuticles
- No white or yellow patches from sun stress
Physical Strength Tests
- Withstand 5-8 mph winds without leaf tear
- Recover from finger-pressure stem tests within 2 hours
- Remain upright after overnight outdoor exposure
Recovery Signs
- Rebound within 4 hours after wilting
- New leaf growth within 3 days of transplant
- No stem purpling from cold shock
Environmental Tolerance
- Endure 10°F below species-specific night temps
- Tolerate 4+ hours direct sun without curling
- Roots hold soil when lifted from tray
Assess readiness with the overnight challenge by keeping seedlings outside once they are perfectly hardened to the chilly night. My broccoli plants received passing grades in my overnight challenge when their leaves stayed perky at 45°F when unhardened plants drooped and flopped in the cold weather. Always check the forecasted low temperature before doing the test!
Do not transplant seedlings with flimsy characteristics the last season's basil was less than firm, having transparent, thin leaves and stems that bent when you touched them. Once we built them up with hardened replacements, the total yield tripled. So, there is a direct relationship between patience and yield quality and quantity.
Read the full article: The Complete Guide to Harden Off Seedlings
