An Orchidist's Miscellany


 Did you know that the average orchid plant comprises mostly water? i nis makes up arounu 90 percent of the weight of an average plant. Different parts of the plant will contain more or less than this, which will be fairly obvious if one looks at a plant. The leaves, for example, contain around 93 percent to 95 percent water, the stem 8.5 percent and the flower spike 30 percent. Obviously some plants are more lush than others, but it is often surprising that the tissues contain such quantities.
If one removes all this liquid, one is left with a small quantity of material - the dry matter. This material can be analysed to ascertain what mineral elements or salts the plant has utilised in its growth. Such analysis can be useful to ascertain the nutrition of a plant, and can assist in the formulation of fertilisers.

A typical analysis of a plant will reveal the following. If one has a specimen weighing, say, one kilogram, 900 grams or 90 percent of its weight will be water. The 10 percent dry matter (100 grams in a 1 kg plant) will contain the following. The figures show not only the elements as a percentage of the dry matter weight, but also, in the example of a 1 kg plant, represent the weight of each element present in grams.

Oxygen 44.5
Carbon 43.5
Hydrogen 6.0 sub total 94%
Nitrogen 1.5
Phosphate .2
Potash 1.0
Sulphur .15
Calcium .2
Magnesium 1.5 =  sub total 3.2%
Manganese .04
Boron trace
Copper trace
Iron .08
Zinc trace
Molybdenum trace
Chlorine .15
Aluminium .1
Silicon 1.2 = 2.8% sub total
TOTAL 100%

Of the total analysis 94 percent of the dry matter is made up of only three elements - carbon, hydrogen and oxygen. As these materials are present in the air and water, if general plant culture is satisfactory the plant's need of these will generally be well supplied. The balance of the materials in the dry matter contain a number of elements, some of which are essential for plant growth to take place, and some which are not required at all. Of the elements in the above list, the last two - aluminium and silicon - serve no purpose in the plant. and have, with some other unlisted elements. been picked up accidentally by the plant. If these are absent, there will be no effect on plant growth and development

Research has shown that in addition to carbon, hydrogen and oxygen mentioned above, the plant must receive adequate supplies of thirteen other elements. If all of these are not present and available in the quantities and form required, vegetative and reproductive cycles will be impeded, and the plant's potential, as set by its generic make-up, will not be achieved.

The thirteen other elements essential for growth fall into two main groupings. Seven elements are present in the plant and required from the environment in minute quantities known collectively as the "trace elements". These are often measured in parts per million, or may be only seen as traces, and are manganese, boron, copper, iron, zinc, molybdenum and chlorine. These elements are generally naturally available in the environment except in exceptional circumstances, or as impurities of applied fertilisers, and therefore generally growers do not have to make special efforts to meet the plant's requirements for them.

Six elements shown in the above list have not so far been discussed and, with carbon, hydrogen and oxygen, comprise the group of "major nutrients". The six are nitrogen, phosphorus, potash, sulphur, calcium and magnesium, which together make up 3 percent to 3.5 percent of the dry matter. The naznes of these elements will be recognised as being the ones most fertilisers aim to supply in the environment. Most fertilisers concentrate on nitrogen, phosphate and potash as being generally the most critically short elements, and the application and selection of the best materials to use is a difficult decision. An introduction to fertilisers and the theory and practice of their use is available on this site.

Site established 9th May 1998