I read about several cobra lily setups in which a pump recirculated water into the container and/or tray, attempting to keep temperatures down and to mimic the natural conditions in which they grow. It sounded cool so I made one of these setups as follows:
- A small white garbage can from walmart
- A piece of styrofoam cut to the size of the garbage can and with a pot sized hole in the middle (see orange)
- A 6" container with a cobra lily planted in LFS with a handful of pumice (see green)
- A solar powered pump (see gray)
- 1/4" tubing taking water from the pump to the cobra lily pot (see purple)
The garbage can holds distilled water that, when there is sun, the pump moves into the cobra lily pot. The theory is that the white container is able to reflect light and reduce the rate at which the water heats up, and that the recirculating water can keep the cobra lily roots cool (because cobra lily roots are allegedly sensitive to high temperatures).
Alas, it seems this theory does not hold in practice.
Take a look at this plot showing the air temperature (red) and the soil temperature (green) throughout the day. At first, as the temperature rises in the morning, the soil temperature is lower than the air temperature. It makes sense that it takes longer to heat up the container, the LFS, and the extra water in the container. However, the soil temperature ends up catching up with the air temperature, and by this point, the recirculating water is quite warm. Furthermore, once the air temperature goes down, the soil temperature takes longer to cool down as now that LFS/water is holding extra heat that also needs to be cooled down.
In the end, both the air temperature and the soil temperature were above 30 C for about the same amount of time (~1h 40m).
So my setup doesn't seem to reduce the time during which the cobra lily roots are hot. Not cool. Maybe it could make a difference if your water container is really large (and thus able to stay cool for way longer), but I have no data on that.
I tried placing a frozen water bottle into the water, and that effectively brings down the temperature, but it's too much effort to do on a regular basis.: With what I've learned so far, I'm leaning towards leaving the setup as is even though it doesn't keep the cobra lily cool... at least I don't have to worry about watering it and perhaps the moving water is good for the plant. I'm going to hope that it can take the occasional heat as temps aren't this high for long.