Finally, the use of compressed bottled carbon dioxide is the most commonly used way to create the gas in a greenhouse for the desired effect. Large greenhouses have burned hydrocarbon fuels for years in an effort to increase growth in their plants. Examples of hydrocarbon fuels are propane, butane, natural gas and alcohol. Gardeners can give nature a helping hand while enjoying the therapeutic benefits of their garden. Gardeners will be able to watch the spectacular improvements that growing hydroponically can bring to their garden. Hydroponics has always been an ecologically sound gardening choice. It uses much less water than conventional gardening and does not erode the soil or add toxins to the environment. In hydroponics plants are grown in a solution consisting of water and nutrients required for a particular plant, or within a system that uses a substrate or growing mix medium. There are several hydroponics techniques and systems that exist for producing plant crops. Hydroponics systems include the nutrient film technique, aeroponics, and the aeration technique. Many hydroponic gardeners have to experiment with different lighting to achieve the best environment for the plants that they are growing. Air pollution can affect the growth of your greenhouse plants and must be monitored if you live in a large city. Signs of air pollution include spotting or twisting of the plant’s leaves, flower and bud fall off, and unusual discolorations as well as poor growth can signal a problem. The yield of the plant is also greater. There are many reasons for the drastic differences between hydroponic and soil plants. Root growth is stimulated in the hydroponic plants due to the extra oxygen. Plants with plenty of oxygen in the root system will also absorb nutrients faster. The nutrients in a hydroponic system are mixed with water and sent directly to the root system. 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. The research for their plans is ongoing. By the 1970’s, scientists and analysts wee not the only people interest in hydroponics.