Take a look at Kiva Rose Hardin's article on Evening Primrose.http://animacenter.org/oenothera.html.
She was the first herbalist to bring evening primrose to my attention and then it self seeded in my garden so I have been using the flowers for a while.
I have made the burns honey with equal parts evening primrose and bergamot flowers and rose petals steeped for 4-6 weeks. I made an evening primrose tincture using the same method as I do for everything else - stuff a jam jar full of flowers, cover with vodka, podge with a chopstick to remove air bubbles then fill the jar with more vodka so all plant material is covered. Seal the jam jar with a screw top lid and let sit in a cool dark place for three weeks shaking ocassionally. Strain into a bottle, label and date.
I use the tincture in my grief formula sometimes when there is a digestive upset associated with the general unhappiness.
Hope this is helpful.