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. 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. 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. Identifying the spider mites will be easier if you use a garden microscope, which will give you a better view of the tiny bugs. 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. Many small greenhouses cost anywhere from $500 to over several thousand dollars, depending on the add-ons you choose. 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. The grower can let a plant go to seed, collect the seed, and start the cycle all over again, which is called germination. Another method is to take stem cuttings, also known as cloning. This process does not work with all plants, but it is considered a highly effective technique. The gardener should also prune the hydroponic plants regularly. Hydroponics also requires the use growing media. 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.