Add in some waste timber that the woodyard uses as pallet spacers and usually ends up in the skip, a bit of joinery talent and voilá - a space-saving rack for the mountain of seedling plants.
Holds 60 if both sides are used (I ran out of cartons)
As a plus, the base of the carton that you cut off (you cut around where the top of the label is, for those wanting to make one at home) can be used as a plant-pot.