I think it depends on your guests, and what you think they’ll do, or if you’re ok with them not planting the trees.
Do many of your guests have yards or space to plant them? If so, are they the type of people to plant a tree and care for it? Are most local to the area so that the same kind of tree will grow in the climate they live in? Of course trees can be planted places other than a yard but thinking its a great idea and actually finding somewhere to plant, gathering the supplies, then going out and doing it is another thing.
I don’t know if the pic is the actual seedling type you’re considering, its hard to tell in the pic but they look like evergreens, which are the usual type of tree sold as favors. Depending on the type of tree used, the amount of care needed can vary, and some types of evergreens can require quite a lot of effort to keep them alive for first year or two. Unfortunately many trees sold as favors are chosen by vendors based solely on how “cute” they look bundled up rather than on factors that would help people actually grow them. I’m not sure if its hard to find trees that are relatively easy to grow…
I don’t know if its an option but if you really love the trees maybe you could have some trees and some birdfeeders so guests can choose based on what is most practical for them?
Although they don’t double as décor, I think the water bottles are a great idea, very practical, and I’d be thrilled to receive one as a guest. If I wasn’t confident that many guests would plant the trees & hang the feeders I’d probably choose the bottles (I wouldn’t like to know that all the baby trees I sent home with everyone would be thrown away.) Since so many people carry bottled water I’d like that it could have a big impact right away. The bottles could be to “dressed up” to look nice on a favor table in an eco-friendly way, maybe paper sacks tied with ribbon or twine?
If you decided not to use trees or feeders as favors you could always use some as décor if they go with your theme and then plant/hang them yourself or share with family and friends you know would use them.
Honestly if I sent the trees or feeders home with most of my guests many would end up being thrown away but I could also see the point of view that even if only a few trees were actually grown it’s a good thing.
I think the eco-friendly favors are a great way to give a gift, reflect your beliefs and share them with family and friends, make an environmental impact, and encourage others to be green all at the same time.
And of course none of the opinions may matter at all to you if you have your heart set on the trees…a lot of wedding planning isn’t at all about being “practical!”