The oldish, commercial, heated hothouses I have have a floor with a layer of polythene which is black on one side and white on the other - with the white side facing up.
What are the pros and cons of this ? Is worth throwing some down on the floor of the polytunnel I'm putting together. (Unlike the hothouses, I do not intend to heat the polytunnel overnight, and I'm less concerned about the speed of plant growth and more concerned about raising the minimum temperatures at night)
White up reflects more light to the plants, and keeps the soil cooler (from sun) probably also keeps fuel-based heat in the soil better if the ground was what was being heated in the commercial hothouses. If the air was being heated, makes little difference.
Black up warms the soil more effectively from sun.
Either should block most weed growth under them.
I'd guess that there's probably a small benefit in the "black-up" direction for overnight temperatures in the unheated case, but I don't know how significant that might be without some actual experimental data.
