For impoverished people who live in a terrain or climate inhospitable to agriculture, hydroponics offers a means of growing food. In areas where food is traditionally produced, but where fields are over crowded or stripped of their nutrients, hydroponics is a way food can be produced using a minimum of space and resources. Dry ice can be used in small greenhouses, especially if a cooling effect is also desired. Dry ice, which is solid carbon dioxide, is effective when used in a well-sealed area. The ice can either be used in block form or broken down into small pieces and used a little at a time. Another method is to put the dry ice into a Styrofoam container with holes in it to slow down the rate of evaporation. General plants prefer the pH to stay in the 5.5 to 7.5 ranges as going beyond this range inhibits certain nutrients to become less available for the plant to absorb. The key is to monitor the nutrient solutions on a regular basis to make sure the pH is at the right level. Hydroponics is the practice of growing plants without soil as hydroponics cultivates plants in nutrient-rich water. 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. Many people who grow their hydroponic plants in a greenhouse will also find that they need the correct amount of carbon dioxide in the air in order for their plants to flourish. If there is a large infestation then there will be webbing visible after a light misting of the plants' leaves. It’s a good idea to take time, and find out how many of your plants are affected. Determining the number of spider mites in your garden, the size of the area they cover, and the size of the infestation will give you an idea of how to eliminate them. Using hydroponics to grow plants can be beneficial for many growers. Hydroponics allows plants to be grown faster and with less of a hassle. 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.