How to combine two render passes into composite node

I’m trying to combine two render passes, one with a background and flower and one with a sun to send to the composite node. (Both of these are image planes.) I tried using the Alpha Over node, but it sets up an either/or situation. If I put the Fac at zero I get only the background and flower. If I set it at one, I get only the sun. I would really appreciate some help with this. My goal is simply to be able to manipulate the sun separately from the background – blur it, change color etc. If there is a better way to achieve this goal, I’m listening. Please see the attached image for my node set up. I have the Fac set at 0.5 which gives only a faint image of both the background and sun. Thanks.

Render the sun with a transparent background (Render / Shading panel set alpha to transparent) then use the alpha over node

Thanks so much Richard! It worked. Did anybody ever tell you that you are a genius?