Reply by Vicki

Here’s my 2 cents, from having made lots of things for the yard/garden. The sun and weather are trecherous on these projects and make the wood move in ways you can’t imagine. Add wet dirt to that and you can see where this will lead. If it were me I would use deck brackets, the kind that have a 90 deg. angle. You can use deck screws to attach your 2X10 to your post. That will be on the inside and hidden by dirt and not seen. Line your bed with landscape fabric before filling with dirt.
Vicki

-- Vicki on the Eastern Shore of MD