Answer: Mondo grass spreads by underground rhizomes so keeping the soil moist will help the plants grow and spread. As for weeds, I'd suggest hand pulling the existing weeds and then applying a pre-emergent herbicide to keep new weeds from sprouting up. Unless you are growing the dwarf or semi-dwarf types of Mondo grass, you may be able to use a product called Image. Be sure to read and follow label directions.
If you want to know everything about growing Mondo grass in Hawaii, here's a publication from the Hawaii Department of Agriculture that may help:
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