Each Planter Well will irrigate 9" of soil beyond its edge, so one 36" Planter Well reservoir will keep the soil moist in a window box or planter that is 54" long.
Rules Of Thumb for the 36"L x 8"W x 3"H Planter Well Reservoir
Using One (1) Planter Well
36"-54" Interior Length x 8"-14" Interior Width x 8"-14" Interior Height.
Using Two (2) Planter Wells
75"-99" Interior Length x 8"-14" Interior Width x 8"-14" Interior Height.
Using Three (3) Planter Wells
114"-144" Interior Length x 8"-14" Interior Width x 8"-14" Interior Height.
