Table of lettuce growing in media

NEW: Evaluation of Recycled Materials as Hydroponic Media

Congratulations to Grantham Scholar Nicole Kennard on the publication of her Master’s work. This work looks at using recycled growing media in hydroponic systems.

The need for alternative growing media for hydroponics

almond shells can be used as an alternative growing media
Almond shells before processing; received as an agricultural waste product from Spain.

This study aimed to find sustainable material alternatives for conventional soilless growing media used in hydroponic (soilless) crop production. Common growing media used today include peat, perlite, and rockwool. However, these materials have drastic environmental impacts.

Peat is a nonrenewable resource which is being rapidly depleted across the world. The extraction of peat from the natural environment releases sequestered carbon. It also destroys natural habitats, and degrades the quality of groundwater in these areas. Perlite and rockwool are both manufactured in energy-intensive processes and they are not biodegradable or easily recyclable.

Thus, Nicole saw a need to find waste materials that could be used as growing media in the specific local contexts where hydroponic production is important.

Almond shells as a recycled media in hydroponics

Nicole investigated two recycled materials. These were almond shells and a recycled plastic drainage plank. Almond shells are an agricultural waste product, and the planks were made from industrial and municipal plastic waste. In this way, Nicole’s research supports the creation of new products and markets within a circular economy. And it promotes the concept of cascading systems by using these wastes directly as feedstocks to drive further food production.

alternative growing media diagram from research
An overview of how novel, sustainable growing media, recycled from various waste streams, can fit into a circular economy framework.

For example, the waste almond shells generated on traditional soil-based farms can now be recycled and used within soilless food production. This allows for a regenerative system that maximises food production through the use of different growing methods for different spaces and land types.

Nicole carried out a germination and greenhouse growth trial. She found that, in comparison to perlite, yields were reduced by 52% in almond shells and 72% in the recycled plastic planks, although lettuce grown in the almond shells still obtained commercially relevant yields. Reduced yields in almond shells were likely caused by the shell’s high salinity, which could be adjusted prior to growing by thoroughly washing the substrate. Lettuce growth in plastic planks was limited by impeded root growth and low water-holding capacity.

The results: recycled media in hydroponics can work

Overall, Nicole’s findings suggest that with minor alterations, almond shells could be used as a sustainable growing media alternative to perlite in hydroponic lettuce production. This could be especially relevant for regions such as the Mediterranean, the Middle East, and the western United States. These areas are the top almond producers globally but also experience significant drought. As a result, they would be ideal for hydroponic food production.

Read the study online

‘Evaluation of Recycled Materials as Hydroponic Growing Media’ is part of a special issue of Agronomy –  Applications of Biochar and Other Organic Amendments within a Sustainable Agriculture and Circular Economy. You can read it open access online.


The main image shows the experimental setup for alternative media hydroponics at Newcastle University glasshouses.