Small grow rooms for the beginning hydroponic gardener are usually slightly larger than a closet and can be completely installed in under an hour. The cost ranges from several hundred dollars to over $500, depending on the add-ons that you think you will need. A small greenhouse can cost considerably more because you will need to either include a cement floor and drainage system or lay other types of flooring such as gravel before you build the greenhouse itself. Hydroponic systems use various mediums that are composed from relatively inert materials that have the ability to retain the food rich moisture and have the ability to physically support the plant roots. Growing media for hydroponics includes, expanded clay, rockwool, perlite, vermiculite, Styrofoam, sand, pea gravel, and other mediums. The actual temperature for the particular plant you are growing will vary. For optimal growth, the amount of light your plants receive can be the difference between life and death. Too many lights can dry out your plants while too few can have your plants stretching desperately towards the lights. All plants respond differently to light depending on the intensity, wavelength and duration it receives. There are a variety of benefits associated with hydroponic gardening. When plants are grown using hydroponics, the roots do not need to search for required nutrients. The nutrient solution is provided directly to them, which results in plant growth, which is more abundant. Incorporating hydroponics into an outdoor garden can help add interest and intrigue. Another method is to put the dry ice into a Styrofoam container with holes in it to slow down the rate of evaporation. Since carbon dioxide is heavier than air it must be placed above the plants in order for it to drift down and surround the plants. Fermentation is another way to create more carbon dioxide in your hydroponic greenhouse. Throughout the last century, scientists and horticulturists have experimented with different methods of hydroponics. One of the potential applications of hydroponics that helped continue research was for growing produce in non-arable areas of the world. Hydroponics was also integrated into the space program as hydroponics easily fit into their sustainability plans.