Quicklime is calcium oxide (CaO), a highly alkaline compound produced by heating limestone (calcium carbonate) to drive off carbon dioxide. When water is added, quicklime reacts vigorously and releases significant heat, forming hydrated lime (calcium hydroxide).
In gardening and agriculture, quicklime is used primarily to raise soil pH rapidly and to reduce certain soil-borne pests and pathogens in specific situations. Because it is highly caustic and can damage plant roots, seeds, and beneficial soil organisms, it should never be applied directly around actively growing plants. Hydrated lime or agricultural lime (calcium carbonate) are generally safer and more appropriate choices for routine soil pH adjustment.
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