If orchid roots rotted because infections set in when roots remain wet too long, neither growing in sphagnum nor semi-hydroponics should be viable growing options. Obviously the mechanism causing death from over watering requires something more than prolonged exposure to moisture. Some of the candidate modes of action sometimes theorized include:
- Suffocation when sodden potting media blocks oxygen availability.
- Suffocation when aerobic organisms consume the available oxygen when breaking down media.
- Extremely low local pH caused by carbonic and organic acids produced resulting from decay.
- Hydrogen sulfide produced by decay occurring in the absence of oxygen.
The growing techniques orchid growers use to prevent root death from over watering address these in two ways.
- They eliminate or reduce the organisms of decay that could deplete oxygen, produce acids, or release hydrogen sulfide. Examples include potting in scoria, Stalite slate, charcoal, Styrofoam, sphagnum, or LECA.
- They assure high oxygen levels throughout the root zone. Common techniques include growing on mounts, in baskets, and the use of sphagnum and LECA.
Semi hydroponics and growing in sphagnum are special cases because they appear in both the preceding lists. Sphagnum resists decay and contains many tiny air spaces that assure oxygen availability to roots. This is true so long as the moss isn’t so saturated that the spaces are filled with water. The LECA used in semi hydroponics does not decay and is porous to oxygen.
K-Sci
Mechanisms causing root death
Threaded Mode
