According to the horticultural experts at the University of Saskatchewan, most houseplants need humidity levels at about 60 percent to survive life indoors. This is also the level that is optimal for human beings. Unfortunately, the conditioned air in our homes and offices lower the humidity indoors. Plants are a great tool for stabilizing the humidity in a room at optimal levels. If you only have a few plants on hand, practice a few cultivation tricks to help optimize their humidifying power. Purchase a humidity gauge to keep track of the humidity indoors. Add more plants as necessary.
Place your houseplant's pot in a larger pot (at least 2 inches larger). Fill the space between the two pots with peat moss. Water the peat moss when you water your plants, so that it is kept consistently moist. As the water evaporates from the peat moss, it will increase the humidity around the plant. It will also keep your plant moist, which will encourage it to release more water into the air.
Fill the saucer beneath the pot with medium-sized pebbles. This is a great trick for plant's that are too large to move into a larger pot. Keep the saucer filled with water (including the runoff from the water you use to water the plant) to increase humidity levels in the room.
Keep the plants in the room close together. As water evaporates from one plant, it will help to keep its neighbor hydrated and keep the individual plants from drying out. This is also a great tool if you work in a cubicle and cannot bring enough plants to work to humidify the whole room. Cluster the plants as near to you as possible.