Why do seedlings wilt after being moved outdoors?
Written by
Julia Anderson
Reviewed by
Prof. Charles Hartman, Ph.D.Seedlings wilt after being moved outside. This generally happens shortly after a shift in the environment. Last spring, for example, within a few hours, all of my broccoli seedlings fell over, as the intense heat, blistering sun, and wind drew out moisture faster than the roots could respond. In shocking circumstances such as this, a stressor quickly enters the picture. However, when overcome quickly and modified environmental care is maintained, your seedlings typically recover.
Sun Overexposure
- UV rays degrade chlorophyll in unhardened leaves
- Direct sun raises leaf temps 15°F (8°C) above air
- Leaves lose moisture 3x faster than indoor conditions
Wind Desiccation
- Breezes strip protective leaf moisture layers
- Stomata close, halting photosynthesis and nutrient uptake
- Stems dehydrate, causing irreversible cell collapse
Rehydration Steps
- Soak soil until water drains from pot base
- Apply diluted seaweed extract to boost root uptake
- Cover with plastic dome for 12 hours
Gradual Reintroduction
- Day 1-3: 1 hour morning shade, 0 direct sun
- Day 4-6: 2 hours morning sun + windbreak
- Day 7+: Add 1 hour daily until full exposure
Avoid repeat wilting with *30% shade fabric* and temporary wind barriers. I have taken to zip-tie burlap to tomato cages now, and it cuts wind speed by 60%, while still allowing light interception. For plants that have sun sensitivity like lettuce, put them under patio umbrellas during peak UV hours.
Purchase a soil moisture meter, which costs $20, rather than rely on guesswork! My soil moisture meter has a probe that revealed basil roots were drying out 2x faster outside than indoors. For plants in the hardening step, water 2x a day, and don't fertilize until plants become established.
Read the full article: The Complete Guide to Harden Off Seedlings
