If you could get mdf ash would it be toxic to put it near edible plants. I know mdf gives of fumes while burning, that is another issue, but assuming you had ash already burned would it be toxic to use near vegetables etc? I'm assuming it would be for anyone eating, is that right? Also what about cardboard ash?
I would not use it personally due to MDF is filled with chemicals & is a "known human carcinogen" associated with nasal sinus cancer and nasopharyngeal cancer, and possibly with leukaemia in June 2004 Heck, I don't even like it in my house since it leeches formaldehyde and other volatile organic compounds.
I agree with pakanohida, you do not want to risk it, ash will still contain much of the bad things. In chemistry analysis we burn things to get to the ash stage for measuring elements that don't burn, which most heavy metals are. MDF manufacture techniques are very harmful to the people who work in the factory. I certainly would not use the ash, heck, I won't use MDF in building cabinets or anything else just because of the risks involved with its manufacturing.
Agreed, newer formulas seem to be improving but its not something I can recommend in any form quite yet.