Osmo oil. But I wouldn’t bother, they’re not designed to last long. Finally got a pair of blue tits nesting in a box I put up 8 years ago, I think they like it weathered.
Got a couple of little wooden insect houses (!) for the garden, and a bird box, from Wilko.
Small print on the label says they recommend applying a "suitable non toxic wood preserver or varnish".
I've looked online and in Wilko and there wasn't anything I could see that gave a clue as to what was (or wasn't) "wildlife friendly".
Any advice gratefully received.
Osmo oil. But I wouldn’t bother, they’re not designed to last long. Finally got a pair of blue tits nesting in a box I put up 8 years ago, I think they like it weathered.
Fair point about the expected life of the boxes. Just thought it was nice to bang them up and have them there for a few years.
I looked at one of the Osmo exterior products and it said it contains "biocides to resist the growth of algae, mildew and fungal attack". I'm not sure whether that would harm birds and insects!