Gardeners' Lore/Law/logic.

In a new house, don't disturb things too much until you see what's going to come up - and WHERE.
Not that we've had a new house for over 25yrs but the same applies to plant pots.
This one has been lurking in a corner, for the simple reason that I hadn't a blind clue what was in it. Apparently the departing neighbours donated them as they departed. Even Gaffer forgot - enter THAT in the Log as an unusual incident.