Just shoot something stationary like a battery placed on a table. Use tripod and set on timer, or use release cable if u hv. Vary the aperture and see the difference. The pix u posted could be due to either motion blur by the plant itself or handshake.
1. shutter speed. I think you r using ur tele at the long end. the rule of thumb is the shutter speed shld not be less than 1/focal length. So if u shooting at 200mm, then the shutter must be 1/200 or faster.
2. this is a rule of thumb. if, eg u hv been to NS and are a sniper or marksman, then maybe you can shoot as low as 1/60 ~ 1/80 even at 200mm and can still get UBER sharp pic. But success rate will drop, ie maybe 5 out of 10 shots are that sharp.
3. aperture do affect sharpness namely the parts of the picture outside the DOF (depth of field) is not sharp. But it is a different kind of blurness (called bokeh) from those in your pic. In fact your pic has no sharp at all but all blur. Thus it is most likely low shutter speed. check your EXIF.
4. and then WHAT is sharp? for me sharp is I can see all significant details at 100% zoom at the least, if not more. And 100% zoom means displayed at the native resoluton of yor display media, eg for a LCD/CRT, with a native resolution of 72 dpi, and if your picture is 3000 x 2000 dpi, then you ought to view the image at 42"x28". If at that size you are not getting details where you had focused then it is not sharp.
5. Technically sharpness is defined by the ability to tell apart closely spaced alternating black and white lines of a certain constant contrast ratio. This measure is used to specify the lens sharpness in something called an MTF chart. You can find it for your lens. But hard to translate these data to real world image. So use your eyes at 100% zoom and if you hv opportunities compare with another lens.
But you first need to overcome your hand shake and use an appropriately high shutter speed to get some sharpness where you have focused.
1. mount camera on a steady tripod (to eliminate chance of camera shake)
2. use fast shutter speed (also to eliminate chance of camera shake)
3. shoot stationary object (to eliminate subject movement)
4. shoot at a place without the wind factor (also to eliminate subject movement)
5. have enough light to shoot with a fast shutter speed and stop down your lens at least 2 stops
6. have enough DOF to cover your subject