The answer is to do what all the top professional nature photographers do: cheat. In the best traditions of skint photographers everywhere, I've used a few simple everyday items to hold the flower stationary and prevent it from blowing about.
Yes, that’s exactly what it looks like, a short length of bamboo cane taped to an old tripod. The business end holding the plant stationary is even simpler:
It’s just an old clothes peg wedged into the end of the bamboo. The weak spring and the indentation in the jaws of the peg mean that it won’t crush and snap the stem of the plant, but will hold it firmly enough to prevent it from moving despite the fairly stiff breeze that was blowing on the day I took these shots. Alternatively you can achieve the same result using string or wire twist-ties.