A method of installing a roof planter assembly includes providing first and second planter modules each including a bottom wall and a plurality of sidewalls that cooperate with the bottom wall to form an interior space adapted to receive plant matter therein, wherein at least a pair of the plurality of sidewalls cooperate to form a corner therebetween, the corner including first and second portions along a length of the corner and having bottom and top edges, respectively, that are entirely horizontally offset and spaced from one another.

Provided is a method for growing a plant using a water-absorbent resin that is less prone to be deactivated by calcium ions, magnesium ions, or the like in soil, water, or a fertilizer. The method includes mixing a first water-absorbent resin containing a crosslinked polyvinyl alcohol and a crosslinked phosphorylated starch or a second water-absorbent resin composed of a crosslinked phosphorylated polyvinyl alcohol into soil to form improved soil, and growing a plant such as turf on the improved soil. The water-absorbent resin is mixed in a granular shape into the soil to afford improved soil. The first water-absorbent resin includes those in which polyvinyl alcohol itself, a phosphorylated starch itself, and polyvinyl alcohol and a phosphorylated starch are crosslinked intermolecularly. The second water-absorbent resin includes one in which a phosphorylated polyvinyl alcohol itself is crosslinked intermolecularly.