Chip,
In addition, try to think about the depth of field as a tool for composition. With a wide aperture either the roses or tree could have been made the subject without moving position. Tree, would have the roses as a blurred foreground and roses , the tree would be blurred out and probably a distraction unless you took a vertical shot and centred the blurred tree? Don't get too hung up on the rule of thirds, it works 90% of the time but rules are made to be broken!
Tip I was given recently is to sweep your eye side to side in the viewfinder and remove anything that doesn't contribute something to the image, easier said than done but it's all good practice.
Here's very quick tweak, removed some of the extras that distract, and blurred out the foreground to show you what the depth of field can do. By no means perfect but you can see the pic has a focal point now. Feel free to ask me to remove this if you'd rather not have folks play around like this! ;-)
