Shading Rate in Greenhouse Affects Indoor Performance under Different Light Intensity in Mentha citrata

To investigate the effect of shading rate in greenhouse and indoor light intensity on indoor performance of lemon mint (Mentha citrata Ehrh.), plants were grown at different shading rates (0%, 50%, 75%, 95%) in greenhouse for seven weeks and two indoor light intensities (9 and 50 µmol·m^-2·s^-1 PPFD) for 16 weeks. Stem elongation tended to increase with increasing shading rate. Plant height under low indoor PPFD was higher than that under high PPFD. Internode elongation was similar in all treatments. Chlorophyll content was higher under low PPFD than high PPFD, regardless of shading rate. And there was no significant difference in chlorophyll content after 23 weeks among shading rates under each indoor PPFDs. Hunter's a value of leaves grown under low PPFD was lower than that under high PPFD. Plants under low PPFD had similar values irrespective of shading rate in greenhouse. Whereas, Hunter's a value under high PPFD was highest at 95% shading. Leaf shape index was highest under low indoor PPFD after 50% shading and lowest under high PPFD after 95% shading. Runners were formed in all treatments and the length was ≈60 cm in whole treatments excepting 95% shading under low PPFD. Axillary shoots were formed in all treatments and number and length of axillary shoots were different among treatments. Fresh and dry weights of plant grown under high indoor PPFD were greater than those under low PPFD, irrespective of shading rate. In conclusion, introduction of lemon mint for green interior needs ≤ 50% outdoor shading and high indoor light intensity.