| The chemical elements in fertilizer really are not plant food. They are building blocks of the various plant tissues. The plant makes and "eats" sugar. Without fertilizer the plant will suffer an inability to make its vital parts including the chlorophyll used to make sugar from water, carbon dioxide, and light.
There was an interesting theory in Orchid Review regarding the source of epiphytic orchid nutrition. The author postulated that sap exuded from the host tree washed down in rain. The sap would include the needed nutrients. This author actually collected sap beneath a tree during rain and showed that nutrients were present. As a control he collected the same rain water in a clear area to show it did not contain any nutrients.
Personally I've never believed the bird dung theory. It's too random an occurrence to support the plant. I think the sap theory explains why orchids only grow in cewrtain types of trees. |