If the greenhouse is coated with coolglass, then the whole greenhouse acts as a softbox, but if your card set up faces the sun then shadows are still a problem. By facing your background away from the light source,  a lovely soft light is obtained and even this improves when the sun is obscured by cloud.

To hold the plants, branches of the fuchsias steady for the photographs Pete has included photographs of his stand set-up.

A solid base for standing the plants on

A clamping section at the side to hold the fuchsia branch steady in its natural growing position.

A clamping section at the top to hold the trailing fuchsia steady.

If you consider this stand would be helpful to you DOWNLOAD