I spoke with City People's Nursery and they get their wreaths from a farmer in Oregon; the plants are essentially grown as a crop so they don't have too many concerns about environmental impacts. @SolarKristy do you know anything about this topic?
I am a volunteer photographer for Soulumination and they are having their annual wreath sale as we speak. They provide professional photo shoots to families who have gravely ill children. It is an amazing organization. They collect all their greens from volunteers who bring in things from their yards etc. Then, volunteer artists go to work and create incredibly unique and beautiful wreaths. All sizes and price points. 100% of the proceeds go toward continuing to fund their mission. I got mine and it is stunning. You can find the details at soulumination.org
I did a study way back in grad school on the carbon benefits/drawbacks of different types of Christmas trees. I would put wreaths in the same category as Christmas trees, as long as they come from farms. The biggest winner for Christmas trees are the ones that can be planted again, but cut trees came out ahead of fake ones because of the carbon benefit of growing the trees for several years that would not happen if people did not buy Christmas trees. If you have a fake tree, or wreath, then get a good one that will last as long as possible. So, long answer is as long as the wreaths come from a sustainable tree farm, they should be fine.