Drying rate of Media
 

In another thread, ES stated “ Because LECA is more porous than bark, it will wick water faster from the pot, and a pot full of LECA will dry faster than a pot full of bark. That clashed with my own observations, so I thought it might make for an interesting discussion.

My thinking is that there’s “drying” and there’s “drying out”, if you get my drift.

I have had plants in S/H culture that were accidentally unwatered for as much as 6 weeks or so that were perfectly fine. The reservoir was bone dry and the LECA certainly appeared to be dry, but the condition of the plants - especially the roots - suggested that there had been some source of moisture (humidity) within the pot to keep them healthy and not desiccated. Plants in bark, when unwatered for that long, would have been far more shriveled.

Of course, a lot depends upon the specific bark or LECA used, size, porosity, packing density, etc., but I’m thinking there is surface moisture and that held internally. The former can be absorbed by the plant if it happens to come into contact with the roots, but the internal moisture can still support the plants, to a degree.

The particular LECA I had at the time apparently had internal porosity that communicated well with the surface, so it both absorbed a lot and released it well. I don’t know if the same can be said for any bark.

I was commenting based on my observations. My 1 quart/liter S/H containers full of LECA will be bone dry after a week with no water. Plants in bark I go to repot are almost never dry at the center of the pot after a week with no water, not even Phals I think are dry.

It's possible what I think is surface dry LECA might have water inside the pores. But these containers feel light.

i have been thinking about this thread for a few days and i think i reconciled the anecdotal observations....bark, in general, will form a tighter packed fit and have more space for contact between the pieces and less air. bark will also degrade which will further reduce the air and increase the area of contact in the interior of the pot. so, if the bark gets wet and then dries out, the inside where it is broken down there is an area with less air circulation and greater water retention. With leca, it is generally uniform as the air spaces are constant throughout and there is no detritus to stay wet and soggy

One C. walkeriana I'm growing in a LECA-filled basket requires more watering than its neighbors in a LECA bark mix, as evidence buy greater shriveling during the winter months when watering is reduced.

Consider that bark will absorb more water as it brakes down, whereas LECA doesn't. However, it may be that LECA will take in considerably water if kept moist for long periods, such as with S/H.

To determine how short term wetting vs longer term soaking affects LECA, I weighed 2 cups of LECA then drained and weighed it at intervals as it soaked. The amount of water absorbed was:

1 minute 37 gm
2 minutes 40 gm
3 minutes 44 gm
4 minutes 46gm
30 minutes 52 gm
60 minutes 54 gm (1.9 oz or just under 2 T.)
18h 76gm (2.7 T)
48h 101gm (3.6T)
It appears that LECA continues to absorb more water as it soaks, but it will take a bit more time to find out how much water it can absorb in the long run with S/H. - CONCLUSION IT HOLDS A LOT

An A-B comparison with potting media wouldn't be terribly meaningful as it would depend on the media (e.g. Orchiata vs sphagnum).

Edit: Clearly, LECA takes in considerably more water given a longer soak and it stands to reason that water deep in the LECA would keep the pellets moist longer. This may account for the difference in observations - a drench doesn't get as much water into the LECA, whereas much more water enters with a good long soak (as in S/H).


-Keith

I would think environmental differences would have an effect on evaporation rate, as well. Since it is much drier in the desert southwest than in the gulf states, evaporation would be much quicker for ES than for Keith...or Ray, for that matter. Interesting subject.

I think Keith's experiment describes my observations well.

Dusty - certainly the ambient conditions will affect the drying rate, but I doubt it effects different materials differently, but if so, it's probably insignificant.

Agree. I updated again. The amount of water in the LECA is still rising, even days later. The amount of water LECA holds if given time is astonishing. But if just moistened it will dry quickly.
I wanted to know. :)
-Keith

The surface area of a pot full of bark in aggregate is much smaller than a pot full of LECA due to the clay's porosity.