https://www.ozervnews.com

The "Black Boy" heater you refer to is actually quite a modern device and still sold in the thousands to help fight frosts in the intensive fruit and wine growing regions. I use this one to protect an apricot, nectarine and plum tree. Some years I spend around a hundred dollars on diesel (illegal to burn waste oil now) to help protect about $50 worth of fruit - Bizarre I know, but once you start, it seems a shame to give up. Hardly used this year and all three trees have a bumper crop - already harvested the apricots Yum

Cheers Chris