I've never heard of this method having some magical properties. I fnd that when planting out, I break up the soil and incorporate some garden lime, blood, fish and bone and mulch it with some potting compost or some home-made. Then some high in potash feed when in-flower. This does the trick for me.

Thanks J,, I think I’ll forget the bananas.

Too much faff, and you'd have to eat loads of bananas ! I think tomato feed liquid would do just as well.

Reply from America
Bananas have potassium in them and this is excellent for tomatoes !

There was further advice

Tomato liquid feed also has potassium in it, as well as other nutrients, and you don't have to eat all those bananas or wait 3 weeks.

I think you will find that it's the fruits that have the potassium whilst the skins have a miniscule amount.

Thanks to all, shan’t bother with bananas.