I use plastic covers to keep the humidity up. Without them, I would
have to water far more frequently. I take the covers off as soon as the
plants have a leaf; at that time I think too much humidity can be a problem.

I use clear plastic so I can see what is happening. I think black might
provide a little more heat (solar water heating installations encourage
black to get more heat from the sun), but I wouldn't think the heat
increase would be enough to matter.

I have some kind of beast that eats my pepper seedlings when I plant
them, so I borrow my wife's Mason jars and put one over each plant for a
few days; once the plant is a little established, the beast doesn't seem
to bother them, and the heat on a nice sunny day can cook the plant.

wrote:
As I wrote in another thread, I am starting seed in peat pots for the
first time, out of curiosity.

I covered the trays with black plastic until the seedlings broke
through.

Now a landscape architect friend has got me thinking:

My original premise: KEEP THE SEEDS IN THE DARK was exploded when he
pointed out that under the ground they ARE in the dark.

Then I suggested that the black plastic would CONSERVE heat, esp. at
night. (Though this is a mild area (So.Calif coastal) the nights are
cooler than the day.) I used to cover seeds in the ground with black
plastic till they broke through.

He exploded that one by pointed out that clear plastic would do just
as well.

I have no arguments left.

Any advice out there?