If you are using pressure-treated timber and are worried about toxicity, look for timber treated with tanalith E—that’s the European approved, child-safe preservative. If it’s okay for climbing frames and swings, it should be okay for gardens.

After that, you’re looking at boron-based compounds, which are water soluble and non-toxic. I think they need to be used on green timbers, though, or at least ones that have a high moisture content.

I use Cuprinol Clear Wood Preserver on bee hives as it’s insecticide free. I’m not worried about it being unsafe, but I know there are people who treat all preservatives with suspicion.

I wouldn’t used old treated sleepers in the UK as most have been treated with very toxic compounds, quite a few of which are now illegal. Untreated hardwood sleepers would be good if you can get them.

Personally, I’d have preferred not to use wood at all and would have opted for reclaimed bricks or concrete blocks as these act as a heat sink (useful in our cool climate) and last for years. But it’s not easy to find enough blocks or bricks for an area as large as ours. I know where there’s a large fire-damaged pile of several thousand but the owners wanted 50 pence a block!

We do have some raised beds without any hard borders and these work well, but the maintenance requirements are different. Wood (and other hard borders) harbour weeds around the edges, while the edges of wood-lined beds can dry out faster (not a problem with blocks). Raised earth beds without borders don’t harbour weeds, but tend to collapse outwards under their own weight and are eroded by birds.

I have another 12 to dig from scratch, and build frames for and plant up. At least I have a better idea of what to do now.

Is there anything that is suitable to treat the wood with? I know you shouldn’t treat them with cuprinol or anything toxic but I was thinking veg oil or something, just to prolong the life of the wood… or is that just crazy talk?