Should seedlings be in direct sunlight?

Although seedlings require ample light for healthy growth, exposing them to direct sunlight too soon can be harmful. 

Their young, tender leaves are easily sunburned, especially if they haven’t been gradually introduced to outdoor conditions.

Intense sun can also cause rapid water loss through transpiration, leading to dehydration, while sudden changes in light, temperature, and airflow can stress the seedlings and slow their development. 

It's best to gradually introduce them to direct sunlight through a process known as hardening off.

New seedlings should be placed in a bright location with indirect light, which provides the warmth and light they need to grow without exposing them to the stress of direct sun.

Once seedlings have developed their first set of true leaves, you can begin the hardening off process by gradually introducing them to direct sunlight. 

True leaves are the first set of leaves that appear after the initial seed leaves (cotyledons) they resemble the mature leaves of the plant and are a sign that the seedling is beginning to grow independently.

Start with 1–2 hours of gentle morning sun, then slowly increase their exposure by 1–2 hours each day over the course of 7 to 10 days.

Once seedlings can tolerate a full day of sunlight (6–8 hours) without showing signs of stress, you can begin leaving them outdoors during the day. However, continue to bring them inside or provide shelter at night to protect them from cold temperatures, wind, or heavy rain.

After spending several full days outside during daylight hours without signs of stress, seedlings should be well on their way to being fully hardened off. If nighttime temperatures are mild and stable, the seedlings can be safely left outdoors overnight.

This marks the final step of the hardening off process and means your seedlings are now ready for transplanting into the garden or their permanent containers, fully prepared for outdoor conditions.