I have several african violets in special clay pots. The pots kind of resemble a double boiler, and the lower pot is filled with water, then the upper section, containing the plant, is unglazed on its bottom half.
If I add fertilizer to the water in the lower pot, will it diffuse through the clay to the soil? Or do I need to apply it directly to the soil or directly water the violet every now and then?
That depends largely on the fertilizer.
Most "liquid fertilizers" are made up of soluble salts that will pass through the porous clay wall. But if the fertilizer contains an organic component, some of the ingredients will not be in solution, but only suspended in the fertilizer. That suspended material will likely be filtered out by the clay surface.
Try dissolving some of the fertilizer in a clear glass with some water and let it sit. If you do not see material settling on the bottom of the glass, it will almost certainly permeate the clay pot. If you see a lot of particulate matter settling on the bottom, it probably will not be able to penetrate the clay surface.
