It depends on how literally you want to interpret “A Midsummer Night’s Dream”
1.Even if you can’t borrow trees or plants, you have lots of time to gather other things.
Approach the landscapers and arborists in the city where you live and find out when they will be pruning trees in the late winter/early spring before your wedding. This spring I came upon our city crews pruning the flowering cherry trees. They were more than happy to let me take some as otherwise they all go in the chipper.
You can set these large branches in pots to look like trees. If you like the look, you can glue on silk or paper blossoms.
2. You can drape tulle or chiffon and sprinkle it with some glitter to catch the light. You can even use butterfly wings if you want to be that literal.
3. Lights everywhere! Candles. Firefly lights! Flameless candles where real candles would not be safe.
4.A large wedding wish tree . Hang the guest favors from it. When the guests take their favor, they replace it with a card on which they have written a message to the bride and groom.
5.Borrow Things! Someone you know must have fountains or plants that you could borrow. Silk plants would work in this situation also. Make sure that each thing is labelled clearly so they can all be returned. Fountains would definitely add a magical touch.
6. Decorate the ceiling. If you don’t use tulle, suspend branches horizontally from the ceiling. You can hang paper lanterns or star lanterns from the branchies with throwies for additional light.
7. Another scrounging idea-get vine prunings and use those to wrap around pillars, posts, branches, whatever you can. The layers of decor will give it a lush woodland look.
8. Use low bowls filled with water and floating candles to enhance the woodsy look.
9. Borrow or rent a black wrought iron gazebo to place over the wedding cake table.Decorate it with vines and fairy lights.
You might find some more ideas on this board: