I have tried to make some self-watering plant boxes where I 3D-print some containers with holes to act as wicks to absorb moisture into a top container with soil. The wicks themselves are packed with soil.
However, some white mold quickly builds up around some of the holes (fairly self-limiting though, it does not get much more than what you see in the attached picture after some days since I first noticed it). I emptied the water and re-cleaned the box, and wiped off the wicks. The existing water had a slight sewage smell to it.
For now, the boxes are directly exposed to light, but will be built in by a wooden enclosure in the "final product".
- Should this be of any concern for the plants growing in the soil? They will be edible greens.
- Can I avoid this, while still using my 3D-printed parts?
Soil being constantly wet is exactly the conditions anaerobic bacteria need to rot everything thats submerged.
The solution is pretty obvious: don't put soil direct under water.
There are many possible ways to achieve that:
Thanks for a thorough answer. I was not aware LECA would be able to act as a wick to any required degree, but that could be a good solution. I'm having some difficulties picturing exactly what you are suggesting with the LECA drainage layer - do you mean in the soil compartment? And then LECA in the wicking baskets with some polyester cloth going from the soil and into the baskets?
I have seen many videos doing it exactly like I do incl soil in the wicking baskets (which is why I went with it), but you are saying that is a fundamentally wrong way to go about it?
Yeah, right. Soil decomposes, a polyester wick or expanded clay won't. Fill the baskets with it, and it will draw moisture from below, without any risk of rot.
If the reservoir is filled completely, the soil still should be way above the water level.
Still, keep an eye out for the moisture grade. Soil and any other organic media aren't allowed to be soaked constantly and usually need some drying in between. Damp is fine, but not wet.