Effect of hydroseeding components on the germination of Mediterranean native plant species

• Four hydroseeding components (growth promoters, dye, surfactant) were tested.
• Hydroseeding components affected the germination of 4 out of 12 native species.
• Components favoured germination in 2 species but delayed it in other 2 species.
• Hydroseeding components did not fully explain poor plant establishment in the field.
• Use of hydroseeding components should be adjusted to the sown species.

The use of native species by hydroseeding has been encouraged for the restoration of degraded Mediterranean areas, but their success is frequently low. Several biotic and abiotic constraints have been reported that partially explain such failure, but the effects of the slurry components on the performance of native species have not been evaluated so far. We used germination tests to assess the effects of four such components – bacteria-based fertilizing agent, biostimulant, dye and surfactant – on the germination of 12 native species used in hydroseeding of quarry slopes.Hydroseeding components significantly affected germination only in four species. Bacteria-based fertilizing agent, biostimulant and a mixture of the four components increased the germination percentage of Thymus mastichina while bacteria-based fertilizing agent and biostimulant decreased the germination speed of Cistus albidus. Component- and species-specific effects on time to germination were observed in Bituminaria bituminosa, C. albidus, Helichrysum stoechas and T. mastichina.The results showed that only a few of the native species studied were affected by a specific hydroseeding component. Therefore, poor establishment of native species observed in the field could not be wholly attributed to negative effects of those components on their germination. These might have contributed to failure in the field by further reducing the low germination speed of certain species. This study suggests that a better knowledge of species characteristics and species-specific responses to hydroseeding components may help to improve the success and the cost-effectiveness of this restoration procedure.