Pete,

don't mention bonfires for plants

You'll set Mark H off

My old work used to burn £1000s worth of plants rather than give TLC

They'd burn 6ft Phoenix reobelenii etc.
I have a poster with "Good homes required" for spare plants. I stand them at the end of the front garden. About 30 self sown seedling green Cordyline australis went last week. and 9 Agave americana pups went over the weekend. The advantage is they appear all over the local area

Never underestimate what people will take for nothing. I just put a wriiten label of hardiness etc, and a reference to the website for more info. Don't bother potting just put in supermarket carrier bags. Will be 100 or so self sown Trachycarpus seedlings, 1 to 4 year old, in the next couple of weeks
Bonfire and compost heap really has to be the last resort.