Any ideas what the hole is in floor of my greenhouse?
In the middle of the concrete floor of my greenhouse is a rectangular hole approx 2feet x 3 feet, 6 inches deep, lined with metal and filled with gravel. I’ve been wondering what it’s for, it completely central so you have to stand/walk about it and can’t put plants in it. Thought maybe a water reservoir to stand pots on if you go away for a length of time, but just read something about heat sinks in greenhouses. Could this be one?! Husband has offered to fill it in but it’s obviously got a purpose, just haven’t worked it out yet 🤨