Did you harden off the plants before putting them directly in the sun? If not, it's probably just sunburn.

Agree - sun scorching from not hardening them off well enough first. Give it some light protection from the full sun until it has a chance to recover.

Dave

What zone are you in that would help, Spinach likes cooler weather, I always plant my seeds in the ground as they do better then transplanting.

I'm in zone 4 Canada .. I did hardening them but only for a few days, that's probably why! what should I do to protect them from the sun, put a black plastic bag on them ?

Did you spray, spread any thing around them, like slug bait, fertilizer, lime, ... ?

I direct sow them around mid March and let them do their thing. Now getting harvest ready. This way you dont have to care for them until they emerge.

For future reference you never cover plants with black plastic bags. The goal isn't total darkness but simply reduced sun exposure for a few days while still letting some sun and air in.

A semi-transparent gallon plastic milk jug with the bottom cut out and the cap left off works, so does any of the many row cover fabrics or plant protectors available. Waxed paper cone with some small holes cut in it and wrapped around an upside down 3 ring tomato cage works until it rains.

You just have to think outside the box.:)

Dave

Seysonn, I didn't spray or fertilize yet !! .. you still plant even if their 4 foot of snow out ?
Thanks for the advice Dave.

Seysonn, I didn't spray or fertilize yet !! .. you still plant even if their 4 foot of snow out ?
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course not. You cannot plant transplant either.
Cool crops like cool temperatures. When you start and grow them inside (LIKE in 70F) they get shocked. So with 4 ft snow on the ground I would not rush it. I start peppers and tomatoes 6 to 8 weeks ahead of time. Because it makes a difference. Cold crops not worth it to start inside, for me.
YMMV