Indoor greenhouses make it possible for people without adequate yard space to grow plants indoors. They are also a good home for plants during the cold winter months and a place to control the habitat of more fragile species all year round. Whether you make the greenhouse yourself or buy and build a pre-designed kit, the fundamentals of an indoor greenhouse are the same.
Greenhouses allow short-wave infrared light into the structure through the glass or plastic windows, and convert the light into longer infrared waves. Those waves are unable to escape the greenhouse, and remain inside, heating the air inside the greenhouse. This can occur by natural sunlight filtering into the structure, or by specially placed fluorescent bulbs or bulbs designed especially for plants.
Greenhouses hold in heat, as stated above, by not allowing long wave infrared light to escape from the structure. If the structure is well sealed, the temperature can be kept high enough to mimic hot summer and even tropical weather. It can be lowered to suit the needs of just about any plant. Thermometers are necessary when having a greenhouse to make sure the temperature doesn't get too high or too low to sustain the plant life.
A key to maintaining the health of the plants is making sure your greenhouse is properly ventilated. Ventilation can help control the temperature of the greenhouse. Increase the ventilation, and you decrease the temperature as more fresh air from outside the greenhouse is let in, and some of those long wave infrared light waves are let out. Ventilation helps deliver a healthy supply of oxygen to the plants, and good ventilation will help control excess moisture and humidity in the greenhouse, preventing soil mold.
By controlling the heat and ventilation in the greenhouse, you can also control the humidity. Greenhouses work to keep in humidity by heating water in the soil of the plants, or in dishes added to your greenhouse specifically for the purpose of increasing humidity. This water evaporates, adding moisture to the air. Add more ventilation, and the greenhouse has less humidity. With less ventilation, the humidity in the greenhouse increase.