Or: Why doesn’t my 3 gallon container hold 3 gallons of soil?
I was told the history of the strange “gallon” sized nursery pots back in college by my horticulture professor, the legendary south Florida plantsman, David McLean.
I’ll relay to you the short version here:
During WW2 the GI’s stationed overseas in Hawaii and elsewhere found exotic plants and wanted to bring them home, but they needed containers, so they went to the mess hall staff and got the used cans that powdered eggs came in during the war. The containers made 4 gallons* of reconstituted eggs so the pots were called “Egg Cans” or 4 gallon pots.
After WW2 some of these GI’s started growing and selling these plants which they collected overseas, and the container nursery business began with the post-war housing boom. Before then everything was grown in the ground and dug when needed or in expensive wooden boxes. The egg cans became the standard size because they were cheap and easy to get. When I first started in the nursery biz in the 1980’s the old timers still called 4 gallon pots egg cans, and I never knew why until college.
*these may have been 5 gallons of reconstituted eggs and 5 gallon pots, my memory is unclear on this.