Hardening off seedlings typically takes about 1 to 3 weeks, depending on the plant type and initial growing conditions.
Typical Duration
- The Royal Horticultural Society (RHS) states that hardening off usually takes two to three weeks , with hardy plants acclimatizing faster than half-hardy or tender ones
- Other sources mention a range from 7 to 14 days as common for most seedlings
- Some gardeners use a gradual increase in outdoor exposure over about a week or slightly longer, starting with a couple of hours and extending to full days outdoors
Hardening Off Process Overview
- Begin by placing seedlings outside in a sheltered, shaded spot for a few hours a day, gradually increasing exposure to sunlight, wind, and cooler temperatures.
- For the first week, seedlings might be outside only during the day and brought indoors at night to avoid cold or frost.
- Over the next one to two weeks, increase the time outdoors and reduce shade and protection until seedlings can tolerate full outdoor conditions day and night
- Avoid exposing seedlings to extreme temperatures or wet weather during this period.
Summary
- Minimum: About 7 days for some hardy seedlings.
- Typical: 10 to 14 days for most vegetable and bedding plants.
- Maximum: Up to 3 weeks for tender or very delicate seedlings, especially if initially grown in warm, protected conditions
This gradual acclimatization helps prevent transplant shock and ensures seedlings develop sturdier growth suited for outdoor conditions.
