Ornamental Production of Organic Basil and Calibrachoa: Fertilisation and Beneficial Organisms

Although beneficial effects of using plant growth promoters (PGPM) for ornamental crops have been reported, few studies examining their effects in organic ornamental crops exist. Consequently, the goal of this study was i) to assess the effect of plant growth promoters on growth and plant quality and ii) to evaluate the performance of mother plants grown organically. For the first set of trials, three fertilisation treatments were compared in main plots (1-conventional control, 2-crab and kelp meal, 3- Gaia green 4-4-4) and three beneficial agent treatments in subplots (1- Mycorrhiza, 2- mix of Streptomyces spp. and Bacillus spp., 3-water control). Three plant species were studied: two ornamental basil cultivars ('Harlekin' and 'Little Magic') and one Calibrachoa cultivar ('Tangerine'). For the second set of experiments, the growth performance of six basil cultivars and three organic fertilisation treatments (1- conventional, 2- converted organics GP, 3-Daniels Pinnacle) were compared. Experimental designs were a split split block with 4 replicates. Growth parameters (height, diameter, leaf area, number of stems, fresh and dry weight) were measured after two cycles of production. Plants were grown in an organic peat-based growing medium (Berger OM1, Les Tourbieres Berger Lte.). Although mineral leaf content varied between conventionally and organically grown plants, results showed that plant growth parameters expressed by plant height, plant diameter, leaf area, and root dry weight of basil cultivars and Calibrachoa were not affected by the treatments studied, while the PGPM treatments increased plant height and shoot dry weight of basil. For both species, although soil was inoculated with beneficial microorganisms, the soil microbial activity (FDA) as well as the Streptomyces spp. and Bacillus spp. soil populations were similar to their respective control plants. The use of organic fertilisers promoted soil biological activity expressed by the FDA hydrolysis compared to the conventional control soil, the crab and kelp meal having an higher activity than the Gaia green organic fertiliser. Root mycorrhization was not significantly different between inoculated and uninoculated plants. Quality of cuttings from mother plants grown under an organic regime was similar to those grown conventionally.