Flowers that have been chewed by bugs, injured by frost, covered by road dust, or whitewashed with bird dew don't work. The wildflower isn't in peak condition. Many flowers like squirrel corn and dutchman's breeches only look good for a day or two before they start to wilt or bugs get to them. Other flowers may look good for several days. The light is bad.
Bright sunshine creates very contrasty light leading to burned out highlights and blocked shadows.
Slide film accentuates this problem. Generally, softer light works better on flowers. In the desert where bright sun is the rule, diffusion cloths and reflectors are almost always necessary to create wonderful photogenic light on the flower. Distracting backgrounds caused by using short focal length lenses is a universal problem. Using lenses in the 200mm focal length with its narrow angle of view and careful use of depth of field will minimize this problem.