Cipher wrote:
Thanks to all who replied to my previous question. Clearly, I've got
some work to do.

I've settled on a pair of 2ftx8ftx2ft high boxes to start the spring.
As for the wood, I'm considering PT for the rot resistance but
something nagging in the back of my mind remembers outgassing of
formaldehyde from PT?

What is "PT"? If it is treated timber it depends on what it is treated
with.

Also, the question of what they get filled with is kind of important
and I've been unable to find anything resembling a consensus. My
current thought is 1/2 topsoil and 1/2 aged horse manure as a start.

What else should I be looking at?

What is the nature of the topsoil that you have access to? What do you want
to grow in it? Half horse manure is rather a lot.

David