Humidifiers are used to add moisture to the air. Maintaining proper humidity in the garden is an important part of ensuring healthy growth. While too much moisture will encourage mold growth, too little will cause plants to become limp and wilted. Plants have differing humidity requirements, and may also need a moister environment during the flowering phase. There are a variety of humidifiers to choose from. Some humidifiers not only add moisture to the air, they are able to remove moisture as well to help maintain consistency.