Between liquid and powder, which have you found most effective?

Do you spray the liquid on the foliage?

Do you spread a thin coat over the soil around baby vegetables? I
have a newly-dug veg. patch in my back yard where young radishes,
spinach and beets are just emerging. To protect them from sun (this
is So. Calif coastal, and we are having some very hot weather) would I
do better to spread home-made compost, which might ?? be too coarse
for the baby plants, or worm castings? The WC are very expensive,
but I'll do it if more effective than compost.

TIA