What are you rendering on to - brick or block.
Waterproofer in the scratch coat is a 50/50 question some say always some say never. "Feb" is the brand name - rather like hoover is for vacuum cleaner
![biggrin :D](https://chat.allotment-garden.org/Smileys/green/biggrin.gif)
Your main problem here is going to be damp from the soil in the raised bed blowing the render off. If you're one coating it rather than a thick scratch and a tight top coat. Id go with a 6:1:1 sand/cement/lime - level it off, let it go green and then rub it up.
I was talking to a plaster a while back who recommended 7:1 or even 12:1:1 personally I think that would end up on the floor.
Dont forget some capping, and a bellcast at the bottom and stainless angles unless you're confident to free hand them.
Thats what I think, but Im sure someone will be around in a bit to recommend something else.