When we pot an Orchid, if we are wise, we use only clean new materials, 
and we remove all traces of the old compost (if any) in which the plant grew. 
This ensures that the newly potted plant has untouched and uncontaminated 
stores of food to utilise for its needs. Hence, we usually find that a newly 
potted plant puts forth strong, healthy new growths. This fact is modified to 
some extent by the state of the plant at the time of potting. In 
the case of a plant which has gone back through disease, malnutrition, 
or the attacks of parasites, the first new growth will probably be below 
average strength, but the general health of the plant will show improvement. Sub- 
sequent growths will increase in size and substance, until the food value of the 
compost has been considerably weakened. Again, if at the time of the repottal, 
the development of a forward growth is advanced, the influence of the new com- 
post will be less evident than when the transfer is made just as the new growth 
is starting. 
If the compost is chosen with due regard to the requirements of the plant, a 
newly potted Orchid should require no additional feeding for some time. 
I refer you to a table below listing the essential elements of plant food and 
analysing the materials most commonly used in Orchid composts. You will note that 
each of the materials has a very large percentage of its bulk made up of organic 
matter. It is the gradual modification of this organic matter which creates “humus,” 
a kind of concentrated plant food containing the salts necessary for the nutrition 
of plants:— 
ANALYSES OF COMMON ORCHID COMPOSTS 
(Supplied by L. C. Home, Brisbane) 
Staghorn Polypodium Todea Barbara Osmunda 
Peat Fibre Fibre Fibre 
Organic Matter and Moisture ........... 97.85 97.96 96.89 96.75 
SFr = ieee ahgs Mike Site Med Rebtel ie bites! 98 44 Be 4 A i 
Wena 156 ohio ctcmeater nee .07 03 Ae ‘14 
PLAN hg Ath ass hg sires .09 16 89 14 
PRUE GR (ite Pe ee 02 .08 12 16 
Iron and Aluminium .................0000 1.20 229 44 .88 
Perera 4 | eo he ele eee ooo 152 1.13 R | 74 
arses 1 Via ie ORO A Een —_ 1.64 AS 1.20 
Serpalager (() ad eek — — — —_ 
Ghlanae nso ee ee eee — —_ os i 
pH value pH value 
Staghorn peat oes 4.99 Cow-dung) ta 6.51 
Polypodium fibre _ ....... 377 Horse-dung scsssssenteceven 7.27 
Osmunda fibre _ ............. 4.26 Fowl-manure i.eeessso 6.67 
In the Orchid’s natural state this humus is supplied by nature from the 
conglomeration of detritus which collects about the plant’s roots in its harbour- 
age of a tree-trunk or branch. The decay and crumbling of the bark, the de- 
positing of dust, the droppings of birds and arboreal animals, the decaying bodies 
of dead beetles, ants and insects, and the growth and decay of various mosses and 
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