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An experiment was conducted to determine which of five substrate-moisture sensor placements best estimates volumetric water content (VWC) for 11.4 L containers filled with Hibiscus moscheutos ‘Pink Elephant,’ as well as the effect of low VWC on sensor measurements. Five sensor placements were tested; three sensors were horizontally inserted into the sidewall at 5, 10, and 15 cm from the base of the container and the other two placements were inserted into the substrate surface either vertically or diagonally. All positions showed a strong linear relationship (r2> 0.92) with VWC determined gravimetrically, indicating they all are appropriate models of container substrate moisture. Sensors placed 15 cm above the base had a y-intercept closer to zero than sensors at 5 cm from the base, vertical and diagonal, but the slope was less accurate (farther from 1, P-value 0.0148) than the vertical placement. Vertical placement had a more accurate slope than 15 cm from the base, but the y-intercept was further from zero. The substrate was dried to 0.11 m3·m-3 during the experiments and became hydrophobic. This substantially decreased the amount of water that could be held at effective container capacity and decreased sensor accuracy. For this species and container size, no probe placement proved superior to the other placements, but choosing a horizontal placement was most practical for pesticide applications, pruning and hand weeding while surface installed placements may be most practical for sensor calibration and ease of installation, and removal.