From ahicks@nmt.edu Sat Sep 14 17:30:21 1996
To: ahicks@quartz.nmt.edu


rec.gardens.orchids #10516 (6 more)
From: ecormie@cc.umanitoba.ca (Edmond Cormier)
Subject: Media compared
Date: Fri Sep 13 13:34:24 MDT 1996
Organization: CUSB
Lines: 56

MEDIA  COMPARED
September 1996

    I was experimenting with shives as a possible orchid medium. While
testing it I thought of doing a comparative study of different media.
     Each litre of medium was soaked for 12 hours in 2 litres of tap water
and then drained.. The water contains 110 ppm of TDS and has a pH value of
7. I did not use water with 0 ppm of TDS in case some  media could have a
tendency to absorb or adsorb salts. No medium did.
     The media are placed in order of best drainage capacity to the least
drainage capacity. The more water drained indicates the best drainage
capacity.

Water                  2 li.                    110 ppm of TDS      7 pH
1. Perlite             1.78 li.                 110 ppm             7 pH
2. Medium bark         1.76 li.                 130 ppm             5 pH
3.Coconut husk         1.7 li.                  1200 ppm            7 pH
4. Klehm's mix         1.59 li.                 120 ppm             6 pH
5. Shives              1.5 li.                  1100 ppm            6 pH
6. Premier's Peat HP   1.46 li.                 460 ppm             6 pH
7. Fine peat moss      1.4 li.                  140 ppm             5.5 pH
8. N.Z. spagnum        1.38 li.                 110 ppm             5 pH
9. Vermiculite         1.18 li.                 110 ppm             7 pH
10. Rockwool           1.05 li.                 160 ppm             8 pH

Notes
1. Perlite has the best drainage and does not change the salts or the pH.
2. Medium bark is too acidic for certain orchids.
3. Coconut husk fiber adds the highest salts. This medium would need to be
leeched by rinsing before using.
4.Klehm's mix (see Orchids,May 1996, p.500) contains peat, perlite,
vermiculite,styrofoam, sand and lime. The lime accounts for the 10 ppm
raise of the TDS.
5. Shives:  it is the refuse of flax straw after the fibers are
mechanicaly taken out.It is the stem of the flax plant cut about 1 cm
long. If it proves useful as an orchid medium there would be no lack of
supply. In fact there are thousands of tons at a plant  at Elm Creek,
Manitoba, Canada. As the TDS is high, shives need to be leeched before
using.
6. Premier's Peat HP has  high salts due to added calcium carbonate and
fertilizer. The fertilizer could be too high to start seedlings or even a
repotted orchids that does not need immediate fertilizer.
7. Fine peat moss brings the pH down at a level adequate for many orchid genera.
8. NZ spagnum lowers the pH the most and has poor drainage.
9. Vermiculite does not drain much but is one of the best medium for
cation exchange.
10. The rockwool used was the pure absorbent one. It has the poorest
drainage.It lifts the pH high. More test should be done on other brands of
rockwool to find out if the results would be different.

     All these media could be used alone or in combination, provided one
takes into account the many cultural factors: light (intensity and
length), evaporation (temperature and air velocity), speed of growth,
amount of fertilizer, pH of fertilizer and water, special needs of
plants.          
Ed Cormier