Great idea from Liz Jacob's on Pinterest
reusing a milk carton for your potting shed
I re-use them for watering. When I plant something permanent, such as a fruit bush, I cut the bottom off a milk bottle and bury it upside down beside the plant. I push the cut off bit over the open end so it doesn't fill up with dirt. Thus I can pour water down to the roots and not lose any by evaporation.