Height is where the weight argument for fiberglass stops being a convenience and becomes the whole decision. A cast concrete column at four feet is a crane or a pallet truck and a permanent choice about where it stands. Jay Scotts put the comparison plainly in their own materials guide: fiberglass planters are much easier than concrete to move around. At this height that means two people, a hand truck and a change of mind if the scheme moves.
Grey does something specific at height that it does not do low down. A tall flat mineral surface reads as a pier or a plinth rather than as a pot, which is why cement grey columns turn up flanking entrances and marking the ends of terraces. The finish has no sheen, so it holds one tone up the full height rather than catching a highlight along one edge, and that is what keeps it reading as mass rather than as an object.
Be precise about what this is: a fiberglass planter in a matte cement grey, not cast stone, and we do not describe it as such. What it gives you is the appearance, a non-porous shell that does not take up the water that expands on freezing, and a weight that suits a roof, a balcony or a set of steps.
