Home > Semi-Hydroponic Culture > Inert Media Comparison > Early Experiments > Buoyancy > Absorption & Packing
Another key to success is the availability of air to the root zone. In nature, orchid roots, being attached to trees or rocks, and only barely covered with forest detritus, are essentially totally exposed to the air. While orchid roots are quite adaptable, in any medium it is still critical to provide air to the root zone to permit gas exchange to occur in as unrestricted manner as possible.
In order to measure the free airspace of the media, the following, rather unsophisticated procedure was followed:
1. The 300 ml containers were filled as completely as possible. They were shaken and rapped on the bench as one might do during potting to densify the medium. "As-is," dry weights were recorded.
2. The media were soaked in water for several days in order to permit them to absorb as much water as possible. Lids were placed on the full containers to prevent flotation of the media and evaporation of the water.
3. The lids were removed, the water level "topped up," and the containers full of media and water were weighed.
4. Excess water was poured from the containers, which were then reweighed containing only the "saturated" media.
The data is displayed below. All weights are in grams:
| Product | Dry | Full | Saturated | Absorbed | Free | %Absorbed | %Free |
| TWFKI | 88 | 204 | 139 | 51 | 65 | 58% | 22% |
| Aliflor | 102 | 233 | 159 | 57 | 74 | 56% | 25% |
| PrimeAgraTM | 108 | 247 | 167 | 60 | 79 | 56% | 26% |
| Stalite | 241 | 369 | 312 | 71 | 57 | 29% | 19% |
(Absorbed = Saturated - Dry, Free = Full - Saturated, %Absorbed = Absorbed / Dry, %Free = Free / 300)
There is more to the story than has been covered so far, but we may draw a few conclusions from the data:
1. Based upon the apparent density, the Stalite is bound to provide a better "anchor" for the plant. By contrast (and reinforced by the flotation experiment), the TWFKI material will provide a poor anchor.
2. The packing densities of the PrimeAgraTM and Aliflor provide the maximum amounts of free space, which ought to provide the best levels of gas exchange at the roots.
3. All of the media are capable of absorbing a significant amount of water within their structures.
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