I leave mine out all winter. I don't drain the planter. It works really well!
The interior dimensions of the liner are approximately 13.5" - which is why you are seeing reference to the 13.5. The actual exterior dimensions of the CUBICO 40 pot are: 15.6 wide (top) by 29.7" (tall), by 11.6" (Bottom/Narrow Base) It holds approximately 7 Gallon (Dry) soil, and 2 Gal (apron) of Water. The CUBICO 40 is the largest of the CUBICO line of Lechuza planters.The way Lechuza models are identified are: by maximum size of the plant they can hold. So, CUBICO 20, Max Size of Plant 22", CUBICO 30, Max Size of the Plant 30", and CUBICO 40, Max Size of the Plant is 40".
For stability reasons, may we suggest another style of planter, the Classico, which would leave plenty or room for the roots of the tree, while keeping it low to the ground, so it will not topple over. The Classico 43 and larger also have a hidden recess at the bottom of the planter so a coaster can be used to easily move the plant when needed.
It's only on one side. The gray lettering is not too obvious.