With Photoshop Elements 9, after I've used the 'Magic Selection Wand', I use the 'Selection Brush' - after zooming right in I can choose to select more pixels or de
If I look at your image above and flip between 1 and 2, I can see a few areas which need selecting
(the green at the base of the rose) and some which need deselecting
(along the stem).
Sometimes after having done this the edges are quite sharp and pixellated, running a soft blur brush just around the very edge usually helps.
With the above 'Mod', I also gave it a few tweaks in 'Contrast' and 'Lighting'.
As for the 'fallen petals'............a bit beyond me I'm afraid, but I'm sure someone else will be able to help! (I would be tempted to pick the rose and set up a stage for it (with a black background). Then when I'd finished photographing it, pull off a few petals and take more photos!).