I always seal my greenery with Leafshine, which is a plant polish used by professional to give a glossy, clean finish to the leaves.
Greenery is cut in the fields is can be quite dirty - sometimes covered with dusty spores (for repopulating the greens). Hard water can leave a spotty residue on some leaves, but that is quickly dispensed with a quick spray of LeafShine by Floralife.
Always spray the greens before adding the flowers. You'll spray those later with a Finishing Touch sealant. The two products are quite different and have different purposes.
The clean glossy finish dries quickly and you'll be free to start inserting flowers if you wish.
Now here' the final, sealed greened spray bar. Lots of coverage for a short piece of foam! If you have a wider arch, simply space out two bars side by side for wider coverage.