A moisture gradient is the change in water content across a soil or potting mix profile, typically from wetter zones to drier ones. In containers, this often forms from top to bottom or from the saturated bottom layer upward as water drains and evaporates.
Gradients develop because gravity pulls water downward while evaporation and plant uptake remove it from upper layers. This creates distinct zones where roots may concentrate in consistently moist areas, while drier regions can limit uptake or cause stress if roots are unevenly distributed.
In container growing, a perched water table can exaggerate the gradient by keeping the lower portion saturated while upper layers dry faster. Mix composition, particle size, and container height all influence how steep or stable the gradient becomes.
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