interesting Youtube video: water retention and wicking of different mediums

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Sep 15, 2008
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Johnson City, TN
Hello all,

If you have 30 minutes to kill, this is interesting:

For those without 30 minutes to kill this is what got my attention.

1. Regardless of the medium over the course of a week all the mediums lost about the same amount of water due to evaporation. This could imply that regardless what medium you grow in, if you do some experiments at the outset you can work out how much water is lost over time and figure out when to water the plants based on the original water content.

2. Lava rock has excellent wicking potential -- better than LECA. Could this work better for us for semi-hydroponics? I am considering transitioning to Lava Rock for a lot of my plants and found this video really interesting: It seems very versatile. That it can be used to spot over-fertilizing very effectively is interesting in itself. For those of us who do not like repotting this looks like a good option.

Thoughts, comments, disagreements, experiences and advice?
I’m not going to waste my time watching that, butI can tell you that while all media may lose about the same amount of water over the course of a week, that is far from telling the whole story.

LECA holds a hell of a lot more water than bark or lava rock because the networks of internal pores are smaller and communicate with the surface. The cellular structure of bark and the glassy nature of lava rock reduces the absorption and hence, release volume.

When I was selling out my plants, equipment, and greenhouse before relocating, I failed to find some plants - two oncidiums (one in bark, one in LECA)3 cattleyas (1 and 2), a psychopsis and a phrag, both potted in S/H - that had been unknowingly knocked off the back of the bench at some point. Even though it had been 6-8 weeks since any watering and the pots were cracked so had no reservoir, the plants in LECA were still doing fine, while those in bark looked really bad.

I can only conclude that the water stored within the pellets must have seeped out, or at least provided a humid environment for the roots, and kept them from desiccation and death.

Lava rock can be a fine S/H medium, but keep in mind that the mineral chemistry is not the same for all, and when a root system goes through replacement upon moving a plant into that growing technique, the old, dead tissue does not wash out nearly as readily as it does in LECA.

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