How to successfully choose growing media

Container production has been expanding in recent years. Choosing the optimal growing media (substrate) requires special consideration, because it is much more than just an anchor for the plant: it can be crucial to successful crop.

A balance between air content and available water is one of the most important requirements of a good growing media.

There are many advantages to using growing media:

•   High yields can be achieved on a limited area
•   Better control over Irrigation and fertilization
•   Easier disinfection
•   Recycling of drainage water is possible
•   Growing media can be used as an alternative to an inadequate soil.

However, growing media also have some disadvantages, such as:

•   Nutrient holding capacity of growing media is low
•   Buffer capacity is low and therefore changes are rapid

What is a good growing media?

Plant roots require air for oxygen supply and gas exchange, and therefore, aeration is critical for optimum plant development. Lack of adequate aeration results in poor plant growth, susceptibility to diseases and nutrient deficiencies.

Ideal growing media provides the plant with an adequate water supply and at the same time contain enough air to allow gas exchange in the root system.

Good growing media are also characterized by high hydraulic conductivity, i.e. ability to transmit water.

Another important property is the growing media’s weight: it should be light weight for easy and less expensive transport and handling. But it should also be heavy enough to provide physical support to the plant.

Selecting the best growing media for your production system

It may be surprising, but in order to choose the best growing media, the first thing you should consider is the production system’s specifications.

These include:

•   The irrigation technique and set up – drippers density and discharge
•   Container size and container shape.

These factors and the growing media must be compatible in order to obtain uniform distribution of the irrigation water and effective irrigation.

Size and shape of the containers

It was mentioned above that the size and shape of the containers, in which the growing media is placed, determine the amount of water that the media hold.

Let’s take a look at the following container shapes:

All containers are of the same volume, and are filled with the same growing media. The blue area represents water. Since it is the same media, the water reaches the same height in each of the containers.

Moreover, the same water content in % is measured at each height (according to the water retention curve of this media). But because of the different shapes, the actual amount of water is different in each container.

This results in a different water/air ratio in each container and in different irrigation management.

Irrigation frequency and amount of water applied in each irrigation are determined by the available water content of the growing media and by the container shape and size.

For example, one irrigation cycle a day is not enough, if the daily water consumption of the plant is higher than the amount of available water in the media.

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