Along one side of the koi pond a gravel bog filter (below) is planted with tall, variegated sweetflag (Acorus calamus), yellow flag iris (Iris pseudacorus), pickerelweed (Pontederia cordata), and water lilies (Nymphaea). Pockets between boulders at the pond’s edge are planted with Japanese irises (Iris ensata), though a few clumps have been infiltrated by the…