Current stormwater management practices (SMP) are not sufficient for maintaining predevelopment runoff volumes. Low impact development (LID) uses site scale SMP to reduce runoff. Bioretention cells, one practice within LID, are small planting beds designed to filter and infiltrate runoff using amended soil and vegetation. The bioretention cell can create a harsh soil moisture regime for plants that has not been adequately characterized. Bioretention cell construction, meteorological, and soil science data were built into the Happy Plant Model to determine how often bioretention plants were saturated and experienced water stress over a thirty year period. The model takes into account eight design factors: soil media depth and texture, gravel storage, ponding depth, drainage area, in situ soil infiltration rate, the landscape coefficient, and root zone depth. The Happy Plant model will aid future studies and landscape architecture practitioners with bioretention plant selection.