The good news, I have discovered, is that it is perfectly okay to put them on the garden - with a few conditions, of course.
Unlike the decomposed remains of leaves, stems and other green plant parts, burned wood doesn't contain nitrogen.
But it does provide phosphorous, potassium, calcium, boron and other elements that growing plants need, and it's also very alkaline and useful for raising the pH in gardens.
You'll need about twice as much of it as lime, but it will supply nutrients at the same time and, best of all, it's free.
However, if your soil has a pH of 7 or higher, it won't be much help, so get a soil test done to see if it'll benefit your garden.
And even if it does, don't use it around acid-loving plants (blueberries, azaleas) or on potatoes, which can get scab disease if the pH is too high.
And keep it away from green foliage and young seedlings - it can burn them, even if it's stone cold.
But you can ...
Spread ashes around the base of hardwood trees. The idea of returning the product to its source, albeit in a slightly different form, has eco-appeal. It's especially good for apples.
Sprinkle some ash on the lawn. Applied lightly and followed by a good watering, the ash will benefit the grass and also foster the growth of clover in the lawn, a soil-improver that provides nectar for bees. Of course, if you're suddenly attracting heaps of bees to the lawn, perhaps resist the temptation to cavort around in bare feet.
Make tea for your tomatoes. Put a couple of kilos of ashes in a permeable cloth bag, tie it closed and suspend it, like an oversized teabag, into a 180 litre rubbish bin of water. Let it steep, so to speak, for about four days, then pour a cup or two around your tomato plants once a week when they start to flower. Lots of vege crops can use a potassium boost, but especially tomatoes.