If it were me I wouldn't but you could sprinkle around your onions and brassicas.

It was used all the time in the early part of the century and the 19th century as a soil improver. My lawn at the front has the blackest soil under it - obviously had soot on it in days gone by (there used to be a couple of cottages on the plot). I have looked it up on organic sites and it is ok to use if well weathered and you do say its well aged. Some of the people who have found it in their soil say their crops are like out of the land of the giants. But check out the organic sites for yourself - google "soot on crops".

Years ago people used to put soot on their gardens to make the soil darker, in the belief that it made the soil warmer, not sure what nutrients there are if any, but the soil does look better black, {especially if you have clay soil which looks grey}

Snag is there are toxins in the soot!