Prepare dry soil surfaces with a water-retention gel before transplanting moss onto them. Water-retention gels are available at most garden supply stores. Follow the instructions on the gel packet.
Attach a misting system to your garden hose to water outdoor moss every day for the first three weeks after you transplant it. This keeps the moss thoroughly damp while it implants itself. The misting system lines your hose with small spray heads that release a fine mist across the ground level of your garden.
Reduce the misting frequency after three weeks. At this point, the moss should be well established and able to live on less moisture. Mist or water your moss when it begins to look or feel dry or brittle.
Spray small areas of moss, such as bonsai pots or indoor terrariums, with a mister bottle. Mist the moss every day for the first three weeks. After it is established and growing thickly, mist it whenever it begins to feel dry or its green color begins to fade.
Place a small humidifier beside indoor mosses if you often forget to mist them. After the first three weeks, keeping the room humid should be sufficient to moisten moss.