Effects of Bed Soils and Plant Growth Regulators on Root Growth of <italic>Hibiscus syriacus</italic> L.

Abstract

Background and objective: As the COVID-19 pandemic gripped the entire world and people found themselves spending more time at home, many households began gardening, and purchased various ornamental plants. Many cultivars of <i>Hibiscus syriacus</i> are grown for their showy flowers, or used as landscape shrubs. <i>H. syriacus</i> is generally known for its high rate of asexual reproduction. However, it is known that the effectiveness of propagation by cuttings can have big differences depending on internal and external factors. This study was conducted to determine the effects of optimal rooting bed soil composition and auxin on the rooting of <i>H. syriacus</i> cuttings.Methods: Cuttings used in this study were from 17 cultivars. As types of bed soil for propagation by cutting, gardening bed soil, sand, mixed soil 1, and mixed soil 2 were used, and the plant growth regulators of IBA and NAA were applied at 500, 1000, and 1500 mg⋅L<sup>-1</sup> concentrations.Results: The rooting rate and number of roots were highest with the combination of perlite and vermiculite. On the other hand, the gardening bed soil showed an extremely low rooting percentage. The root growth was improved in most cultivars when treated by plant growth regulator. The highest rooting rate was verified at IBA 500 mg⋅L<sup>-1</sup> treatment while the number of roots and root length showed good result in IBA 1500 mg⋅L<sup>-1</sup> treatment.Conclusion: In many cultivars, it was observed that the rooting rate and number of roots differed depending on the bed soil. The most suitable bed soil for the cuttings was a mixture of peat moss and vermiculite, and it was possible to increase the efficiency through treatment with a growth regulator, and the efficiency of IBA was better than that of NAA. However, it is necessary to identify which detailed growth regulator treatment is suitable for the root development of each cultivar, because plant growth regulator was less effective and even problematic in some cultivars.