I would hold off on that as the ash has a lot of heavy metals and it will leach into the ground. My two cents.
The was another thread already discussing this. Don't have the time to look for it but to somewhat quote a poster in that thread.... he explained it much better
So does dirt and everthing else. Any toxins you would introducing wouldn't amount to anything. He also went on to say that adding ash to the garden isn't going to help, nor will will it harm it. It's mostly made of inert subtances.
Finally, most of the old timers in this area swear by it especially for the tomatoe plants.
Good? Bad? I really have no idea but my money is on neither and it doesn't provide any benefit nor is it harmful. On the other hand if you had a couple hundred thousand tones of it piled in one area it very possible those toxins could be harmful.
Just an opinon, not cold hard facts.