Safe Plant Substrate for Birds

[Polliwog]

I am not looking to feed a bird soil, but I was thinking of providing my future budgie a in cage growing patch of wheatgrass. Or what if I put a pot outside the cage and allowed the grass to grow in towards the cage. What if the bird pulled out some grass and soil came up with it? What would be safe?

[Monica]

Soil that has not been treated with any sort of chemicals or unnatural fertilizers should be safe.