From ten formulations to five: how CITA selects alternative growing media
PEATLESS combines plant performance, physicochemical characterisation and microbiological analysis to identify the most promising growing media for further validation.
Developing reduced-peat and peat-free growing media requires more than identifying alternative raw materials. The different components must be combined into formulations and tested to determine whether they provide suitable conditions for plant development.
Within the PEATLESS project, the Agrifood Research and Technology Centre of Aragon (CITA) has completed an initial screening of ten alternative growing media for vegetable seedling production. The aim was to compare their performance and select a smaller group for a more extensive validation trial.
Ten formulations and a peat-based control
CITA prepared ten growing media formulations using different combinations of materials. These included composted bark, spent mushroom substrate, wood fibre and compost. Some formulations contained reduced amounts of peat, while others were completely peat-free.
A conventional peat-based growing medium was included as a control, providing a reference against which the alternative formulations could be evaluated.
The ten formulations were tested with lettuce and pepper seedlings, allowing researchers to study their performance in two different vegetable crops.
The formulations were assessed through a combination of plant, substrate and microbiological data rather than through a single result.
Following seedlings from germination to transplanting
The trials covered the period from germination to the stage immediately before transplanting: approximately 35 days after sowing for lettuce and 40 days for pepper.
Researchers first examined germination rate and uniformity. Germination percentage alone does not provide a complete picture, as seedlings also need to emerge and develop consistently across each tray.
Several shoot and root development parameters were then recorded:
- Plant height
- Number of leaves
- Shoot fresh weight
- Root fresh weight
- Root length
Together, these measurements provided a detailed view of seedling development in each formulation.
Looking beyond visible plant growth
Plant development was considered alongside the properties of the growing media themselves. CITA characterised several physicochemical parameters that can influence the conditions available to roots:
- pH
- Electrical conductivity
- Porosity
- Aeration
- Water availability
Some of these properties were previously introduced to students through practical demonstrations during the project’s Fascination of Plants Day activities at CITA. In the current trials, however, they form part of the technical assessment used to compare the formulations.
The growing media were also examined using metagenomic approaches to detect the presence or absence of pathogens and beneficial microorganisms.
Combining these analyses with the plant measurements allowed CITA to evaluate each formulation from several complementary perspectives.
Selecting five formulations for further validation
Following the initial screening, five of the ten alternative growing media were selected to progress to the next stage.
The selection was based on the overall evidence generated during the trials, considering seedling performance alongside physicochemical and microbiological characteristics.
This step reduces the number of formulations while retaining those that showed the strongest overall potential under the initial experimental conditions.
Five formulations have moved forward, but a larger trial is still needed to confirm their performance.
A larger trial with more plants and varieties
The five selected formulations will now enter a more extensive validation trial at CITA.
The next experiment will involve:
- A larger number of plants
- Two lettuce varieties
- Two pepper varieties
- Two experimental replicates
Germination and plant development will be evaluated again to determine whether the performance observed during the initial screening can be reproduced across a broader experimental design.
This progressive process of screening, selection and validation forms part of the PEATLESS work plan for testing and refining new growing media. It allows the project to narrow down the available options before the most promising formulations move towards subsequent validation stages.
