Container Capacity

Definition - What does Container Capacity mean?

The term container capacity, sometimes referred to as water-holding capacity or water retention ability, denotes the maximum amount of water that can be held by a plant’s grow medium within a container before gravity forces the water to flow out of the container’s drainage holes.

The container capacity, which is how much water the container can realistically hold at any given time before it flows/leaches out the bottom, can be altered or effected by a variety of things, the main one being the types of materials that are contained within the potting mix or soilless grow medium being used.

The size of the container, the size of the plant housed within, and the material the container is made of all affect a container's capacity to hold water.

MaximumYield explains Container Capacity

Different substrates hold various amounts of water. Some substrates such as bark and perlite are extremely porous and allow water to quickly flow out of the container. Peat moss and coco coir have small pores and become overly saturated because the water does not flow rapidly out of the container and away from the plant’s roots.

There are several tests a grower can use to determine a container's capacity to hold water. These tests involve measuring the amount of input water and determining how long it takes or how much water it takes until the water is seen flowing from the container. The longer the water takes to flow from the container, the higher its capacity.

It should be noted that a fabric container's capacity is lower than that of a plastic container, because moisture is lost quicker from the sides of the container, rather than a few drainage holes.

Understanding container capacity is beneficial to the grower because it helps determine how frequently to irrigate and how much water to use. A basic understanding of container capacity also aids in stopping fertilizer runoff.

Diseases can be prevented by ensuring that a plant’s root system does not remain overly saturated for an extended amount of time. A plant that has adequate water and oxygen readily available to its root system grows better and develops a stronger root base. Container capacity is an ideal way to successfully measure a substrate's water-holding ability and the rate at which roots uptake the water.

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