Gravel colour affecting germination rate?

[George R. Stilwell, Jr.]

Paul,

I've not had your experience, but it occurs to me thet the temperarure in
the black gravel shouldbe higher since black absorbs more light
than brown - that's why it looks black.

Why that should slow germination is a mystery.

Another possibility is the soluable iron may be higher in the black gravel.
Again, why this would slow germination is a mystery. You could
add a bit of iron to the brown gravel pot and see if it slows germination.
Probably a couple of nails should do.

Like most of us, you'll have to wait for Seedex seeds to arrive to try
this.

Ray