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. Specially formulated hydroponic fertilizer mixtures are required and should be tested after dilution to ensure a pH level of between five and six. This nutrient solution should be changed every two weeks and in between changes should be checked so the volume is kept level by adding more water only and not additional formula. Plants can be placed much more closely together than in traditional fields; as many as four times as many plants can be grown in the space using hydroponic techniques as opposed to traditional methods. Secondly, hydroponics eliminates many of the problems associated with traditional farming that leads to sickly, damaged, or wasted crops. 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. Many gardeners do not realize that the larger their hydroponic garden is, the more their plants need carbon dioxide for respiration. How can you boost the carbon dioxide content in your hydroponic garden? There are five ways that you can increase the level of carbon dioxide in your greenhouse to increase plant growth. For example, marigolds may be planted between rows of herbs in a hydroponic greenhouse. Spider mites will be turned off by the smell of the marigolds and will leave the garden. Biological insect control is another method of pest management through the introduction of predator insects to eliminate spider mites.