How Does Pot Height Affect Water Holding Capacity?

It’s essential that growers find a balance between proper water retention and optimal air space regarding planting containers and pots. However, many factors should be considered when planning for this type of harmony. Substrate composition is the most important, relating to its particle size and incorporation rate. Additionally, aggregates, such as perlite and wood chips, also play a role by increasing drainage within a substrate. One factor we’d like to look at today is pot height. 

Air space and total capacity will vary depending on the volume and height of a container. More pot height increases air space while often lowering container capacity. Additionally, taller containers can help avoid the phenomenon of a “perched water table” which is common in short pots post-irrigation. Furthermore, shorter containers, when paired with a substrate composed of fine particle sizes, can create insufficient air space and lead to root rot. However, “total porosity may remain the same across containers of various sizes as long as the bulk density stays the same,” according to North Carolina State University’s Brian Whipker and Patrick Veazie in a recent e-Gro alert.  

For a practical example, Whipker and Veazie recall an instance of marigolds grown in a taller-than-normal pot. This resulted in more of a substrate being used but with much more available air space. Additionally, plants in taller pots exhibited excessive surface drying, feigning the appearance of severe dehydration despite not needing additional water. This is due to a lower water content at the top of the pot due to increased drainage, which often leads to the consequence of accidental overwatering by growers. 

Conversely, plants in shorter pots also need modified watering practices to prevent overwatering, perched water tables, and disproportionate air space occupation. Again, this could lead to root rot or even plant desiccation. 

As touched upon, growers should lift a pot to determine its water needs instead of examining the state of the top of the container. This factor of container geometry “influences gravitational drainage, and growers should be aware of pairing the correct substrate, container geometry, and watering practices to maintain optimal air and water conditions within the container to promote plant growth.” 

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For more information, details, and tips on the effectiveness of pot and container height regarding water capacity, please read the full e-Gro (Electronic Grower Resources Online) alert “Do Taller Pots Hold More Water?” Additional e-Gro alert pieces from Volume 13 (2024) can be found online. 

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