I needed a mesh insert for my bonsai dish and I didn't want to buy a large pack of them online. This model can be printed, then trimmed to size if necessary. The holes are 3 mm wide, and should be suitable for gritty soil.

I designed this model for a 0.4mm nozzle and 0.2mm layer height. The grid lines are 0.8mm thick, and the model is 0.4mm tall. I suppose other nozzle sizes and layer thicknesses would work, though it may not be optimal.