Question about Anderson flats

[Michael P]

Anderson flats come in two sizes: 15.75x15.75x5" and 15.25x19.88x2.5". Most people seem to use the first deeper size. Are the second size (larger but shallower) rigid enough to support the tree and soil without sagging or flexing? I plan to order some this spring.

 

[Cruiser]

The larger shallower flat will sag a little in the middle when lifted and flex on the sides if placed on a surface smaller than the flat.
The extent probably depends on what’s in them and positioning.
My flats are well-filled with group plantings. The flexing was more noticeable at first so I put another flat underneath to stabilize things. It helped a lot and provided a little cavity for roots to grow down into.

Over time, the flex/sagging will decrease as roots fill the flat.

 

[Michael P]

Thank you!