Wood hardener lengthens the life of deadwood. It hardens punky wood in danger of eroding away, and likely protects against decomposition by pathogens.

Store bought wood hardeners can certainly be used. I’ve tried them, and they seem to apply the resin mostly to the outside layer of wood.

I prefer the recipe I learned in Japan as it’s easy to adjust for penetration, and because it’s cheap. 

Thanks to a subscriber for suggesting this post!

Here’s how to make the wood hardener that I learned from Mr. Suzuki.

Tree resin, collected at the base of conifer trees. Resin is produced from environmental or insect wounds, like the loss of a branch or a borer hole. Over time the resin hardens and looks like a translucent rock. 

Now for the operation: take a hammer and a chunk of hardened resin.

Pound till crushed.

Pour isopropyl alcohol in a jar at a weak dilution, about 1:50, with the crushed resin. Let sit overnight.

Brush onto the deadwood. The thinner you make the dilution, the more it seems to soak into the wood. The isopropyl will evaporate, leaving the resin inside. Apply several coats. If one coat leaves a sheen, consider diluting with more isopropyl.