Hardy hibiscus (Hibiscus moscheutos) are native herbaceous perennial plants. Due to their ornamental nature, variations in flowers, foliage, color, and variety are important. Mutagenesis is a method to increase variation in hibiscus plants, and ethyl methanesulfonate (EMS) is a common chemical mutagen that causes nucleotide substitutions. It converts guanine-cytosine pairs to adenine-thymine pairs. This study aimed to determine the EMS LD50 value for hardy hibiscus. The cultivar ‘Luna Red’ (Ball Horticulture) seed was used for treatment. An EMS LD50 determination study was performed using a factorial randomized complete block design. Three replications of 15 seeds were used for each treatment. EMS treatments consisted of 0, 0.25, 0.5, 0.75, and 1% EMS solution, each treated for 4, 8, and 12 hours to determine the ideal treatment concentration and time. The germination rate, survival rate, and height of seedlings were measured. The interaction effect for germination was insignificant when measuring concentration and time, so the LD50 values were identified for each time separately. The LD50 values for seedling survival were 0.64% EMS for 4 hours, 0.45% EMS for 8 hours, and 0.38% EMS for 12 hours. Notable phenotypic differences between the treated and control plants were observed. There was 92% greater two-month survival in the control plants compared to those treated with 0.75% EMS solution. The control plants were 90% taller at three months after treatment than the plants treated with 0.75% EMS solution.
