After experimenting with the hair particles in Blender I wanted to use the painting from the animatic for the grass in the first scene as I could not get hair particles thick enough and with the same character. After looking through numerous tutorials I could not get partial transparency to work on the images assigned to planes – it was either 100% or 0% which leads to ugly jagged fringes. Eventually I found the answer (which is probably pretty obvious to someone familiar with 3D work): you have to pre-multiply the alpha on the image. Pressing the Premul button after loading the image makes life prettier. It is annoying that a lot of documentation seems to miss a critical point like this and leads to much frustration.
There also seemed to be two ways to go about making this material setting. The one where the alpha slider affects the transpanecy of the opaque parts of the image seems the most logical. The other makes the material’s general alpha slider effect the degree of the alpha. This seems less logical to me as the general alpha should effect the transparency of the whole object not the texture.