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There are permaculture principles and permaculture ethics. The ethics are sometimes referred to as principles as well. I'll keep them separate. The permaculture ethics are at the centre of permaculture philosophy and are broad guidelines of how we should behave towards the earth and towards each other. The permaculture principles, or permaculture design principles , are the guidelines that you follow when you design a permaculture garden or bigger permaculture system.
NASA researcher checking hydroponic onions with Bibb lettuce to his left and radishes to the right Hydroponics is a subset of hydroculture and is a method of growing plants using mineral nutrient solutions, in water, without soil . Terrestrial plants may be grown with their roots in the mineral nutrient solution only or in an inert medium, such as perlite , gravel , mineral wool , expanded clay or coconut husk. Researchers discovered in the 18th century that plants absorb essential mineral nutrients as inorganic ions in water.
A greenhouse (also called a glasshouse ) is a building in which plants are grown. These structures range in size from small sheds to industrial-sized buildings. A miniature greenhouse is known as a cold frame . A greenhouse is a structural building with different types of covering materials, such as a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming visible solar radiation (for which the glass is transparent) from the sun is absorbed by plants, soil , and other things inside the building. Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall. In addition, the warmed structures and plants inside the greenhouse re-radiate some of their thermal energy in the infrared spectrum, to which glass is partly opaque, so some of this energy is also trapped inside the glasshouse.