All of these salts must be thoroughly dissolved before being allowed to circulate around your root systems. Micronutrients are also needed for proper growth of your plants. Boric acid, manganese chloride, zinc sulfate, copper sulfate and iron sulfate can be used in minute amounts in the nutrient solution. This is due to the fact that the plants are not grown in soil. When growing hydroponically, the gardener will need to add all of the nutrients the plant needs to the water. Distilled water will work best for making the nutrients. Hydroponic supply stores sell a variety of nutrient mixes for specific crops and growth cycles. Solution culture uses a nutrient solution but does not use a solid growing medium for the roots. The medium culture has a solid growing medium for the roots such as gravel, sand or a perlite culture. Hydroponic plants are grown in a number of ways, each supplying nutrient solution to the plants one way or another. Though the pesticides used in hydroponics do not run-off and pollute the surrounding environment like the pesticides used on traditional fields, they are still on the plants themselves. The field of hydroponics is filled with promise, and much research is being devoted to solving the concerns that currently stop more farmers from going hydroponic. 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. Fuels that contain sulfur or sulfur compounds cannot be used because they produce harmful by products when they burn. Dry ice can be used in small greenhouses, especially if a cooling effect is also desired. By the 1970’s, scientists and analysts wee not the only people interest in hydroponics. Traditional farmers and eager hobbyists began to be attracted to the virtues of hydroponic growing. Some of the positive aspects of hydroponics include the ability to produce higher yields than soil-based agriculture and they allow food to be grown and consumed in areas of the world that cannot support crops in the soil.