LAUSR

Some herb plants can be adapted to green roof systems when provided with better growing conditions such as irrigation. The aim of this study was to determine the effects of different amounts of water retentive, hydrophilic polymers used in green roof substrate mixtures, on the growth of Agastache rugosa. Coir dust and perlite were mixed at a ratio of 80 to 20% (coir dust to perlite, v/v) (termed C4P1), 50 to 50% (C1P1) or 20 to 80% (C1P4) at a substrate depth of 20 cm. Hydrophilic polymer was added to the substrate mixtures at 0 (polymer: medium (w/v), dry weight basis) (control), 0.25, 0.5, 1.0 or 2.0 kg·m -3 . Our study indicated that Agastache rugosa can withstand extended dry conditions experienced in green roofs. Substrates C4P1 and C1P1 with high coir dust matter are not suitable for Agastache rugosa because of the low growth and poor ornamental quality observed in these plants, especially during the summer rainy season. For the determination of difference in growth, flower development and overwintering of Agastache rugosa among the different substrate conditions, Duncan’s multiple range test was conducted. It was found that the addition of 1.0 kg·m -3 hydrophilic polymer to C1P4 significantly increased the number of inflorescences and resulted in good growth and ornamental quality during both drought and rainy seasons. Moreover, higher overwintering rate was associated with lower coir dust and hydrophilic polymer content. These results indicated that addition of 1.0 kg·m -3 hydrophilic polymer to C1P4 was optimal for the growth of Agastache rugosa in green roofs under dry and rainy seasons.