If Volumetric Water Content (VWC) sensors are to be used in container-grown plants to decide “When to irrigate?” and “How much to irrigate?”, then the lag time from the time water is added to a container at the surface until additional moisture is detected by the sensors must be known. Where should sensors be located? The objectives of the experiment were: (1) to measure the distance and speed of water migration in container mediums in a laboratory setting, (2) to compare water migration in two types of container mediums, a grower mix and a commercial mix, and (3) to observe water distribution directions and patterns. While using a grower designed, custom made mix with VWC = 25.5%, 106 min were required for the water to migrate 7 in. for an average velocity of 0.066 in./min. When this same container medium was dried to 1.8 % VWC, the hygroscopic capacity of the mix was apparently severely reduced. Lateral water migration was adversely impeded in some directions and magnified in others. The probe located 3½ in. to the left sensed water after only 1 min, which required an average velocity of 3.5 in./min. Meanwhile, the probe located 3½ in. to the right of center required 32 min for the water to travel 3½ in. laterally (V = 0.109 in./min). This implies the water traveled to the left 32 times as fast as it traveled to the right. The direction, distance and speed of lateral moisture movement in container mediums are apparently not predictable.