I don't believe you could have prevented it.
We (as humans) can't always foresee what our horses will spook at. Especially since you just started riding this horse, you don't know the horse very well and certainly cannot know things he will spook at.
As far as riding spooks, just TRY not to panic. Sit back keep your heels down and keep riding through it. If its a very big spook and your horse will not stop, try a pully rein.
DON'T slow down near the hedge every time as that will become a bad habit as the horse will think it can slow/stop every time it goes near it.
Don't even look at the hedge, don't even think about the hedge. Your fear of it will only increase the horses fear of it. If you show the horse that the hedge is nothing to worry about, then probably the horse will think nothing of it unless something pops out of it. Which, of course, is not predictable.
Last edited by newbhj; 08-10-2011 at 10:50 PM.