The Surface Layer That Can Help a Container Hold Moisture
Food Systems
Mulch can slow evaporation from potting mix and moderate surface temperatures. University of Minnesota Extension lists options such as coconut coir or a little straw where the container is large enough.
Choose a material that suits the plant and pot. Check the moisture underneath before watering, and make sure the container can still drain. A mulch layer can hide a wet surface as easily as a dry one.
Compare similar containers over a few days to see whether the change helps in your location. Wind, sun and pot size all affect how often you need to water.
Source
University of Minnesota Extension: Watering Container Plants
