Group the layers containing elements of leaf into one group. Now you need to make A LOT of copies. Here's the hint to speed up process: select group, hold ALT key, and click-drag group to move it. Every time you drag it, holding ALT key, Photoshop will create a copy of group.
After each 15-20 copies, hit Ctrl-T, rotate and resize....
...once again, make 15-20 copies, rotate, resize, make 15-20 copies, rotate, resize, etc.....
after about 30-40 minutes of copying, rotating and resizing, entire image is filled with leaves and no background is visible.
Merge all layers and groups into one layer (it is good idea to save backup PSD file before that) and apply the following layer effect:
- gradient, radial, black-to-white, overlay, size:150%, opacity: 20-25%.
But what if I wanted to plant some flowers into the wallpaper? Easy!
Create new layer, set foreground color to white, switch to Pen tool, and draw shape similar o this.
Switch to Pen selection tool (A), select shape, copy (Ctrl-C), paste (Ctrl-V), rotate 180 degrees, move down.
Then, you might already guess... select all, copy, paste, rotate, select all, copy, paste, rotate, select all, copy, paste, rotate, select all, copy, paste, rotate! (Hint - hold SHIFT while rotating).