I found a huge load of decking boards in hard rubbish a while back. Most decking boards these days are made out of merbau, which is a rainforest timber sourced in nations with lax environmental controls. It’s a sad industry for the world…
The wood is incredibly rot resistant and strong. I guess it grows in rainforests in Malaysia and other south-east Asian countries so only the toughest survive. It is amazing for use in the garden as it takes many years to rot so can be used for stakes, structures and garden beds.
I made the boards I found into two garden beds. They are about 240cm by 120cm and about 40cm high. They have a little lip around them to sit on. I really love them. They took quite a while to build but they were easy to do (just a bit time-consuming due to the fact that I was joining lots of different length pieces together). They look really nice and its satisfying to know they came from hard rubbish, they cost nearly $0 to build (just had to buy screws) and that they will probably last 10-15 years or more.
If you ever see merbau wood lying around, grab it.