Perlite is used in potting mixes and as a stand-alone soilless medium for plant roots. It is ph neutral (around 7) and completely sterile, which is critical for rooting plant cuttings. When used alone, it provides perfect aeration and holds the right amount of moisture. Perlite can hold three to four times its weight in water, but never becomes soggy. And unlike soil or organic matter, it never disintegrates. Perlite is also used with hydroponic systems world wide, with superior crop production. When used in potting soil mixtures, perlite lightens the mixture and improves aeration and drainage. This is especially useful for large container plantings. The newest use of perlite is in rooftop gardens. This makes sense, since perlite is proven to grow healthy, viable plants. The main limiting factor for rooftop gardens is the weight. Using perlite over other soil mixtures reduces the weight dramatically, by more than half, allowing gardens to thrive in cities where garden space is virtually non-existent. The added benefit is the green roof also reduces heat gain inside the building. Plant nurseries are also on the perlite bandwagon. With shipping costs based on weight, using perlite reduces these costs without sacrificing plant health on long trips. Aside from its use as a soil amendment or replacement, perlite is used as a carrier for herbicides, pesticides and fertilizers. Perlite is also used to pellitize seeds for easier planting.