Herbdoc has some tips for those of us who go out and collect our own holiday greens:
As I was gathering greens on my property for holiday displays the other day, I came across a small patch of Oriental Bittersweet (Celastrus orbiculatus) in the side yard. This plant is highly invasive and so I immediately cut it down and bagged it for removal, but I know I will have to watch the area carefully as it’s tenacious and will re-sprout in the spring.
That same day a warning from UMass appeared in the local newspaper warning gardeners and homeowners to forgo hanging wreaths or garlands that contain bittersweet or multiflora rose (Rosa multiflora). Although the red berries and hips are very beautiful and are commonly used in holiday decorations, the fruit can easily drop into the soil or be carried off by the birds that eat them. The sprouted seeds lead to massive infestations which in turn crowd out native plants and choke mature trees.
If you are designing your own holiday creations or buying them from a local stand, please steer clear of these two invasives. In the long run, it will save you and your neighbors a lot of unnecessary yard work or money to have them removed.