There’s something about the way foliage looks during and immediately after heavy rain that I find particularly appealing; the greens seem more intense, more vibrant. More saturated!
In the village where I lived previously there was a road that was prone to flooding in such conditions, and this combined with the broad expanse of the village green and the avenue of sycamore trees was a constant temptation to overload in the greenery reflected in the waters.
The “garden” that surrounds my apartment is a far more modest affair, but in the inevitable precipitation of a British Bank Holiday weekend the same effects are present.
The first answer I encountered through google suggests it’s a simple solution; the rain washes away the dust particles that gather on the leaves, leaving them brighter as a result. Seems too easy, though not improbable, however it doesn’t explain why only greenery benefits from that visual pop. Why don’t red cars, blue doors, yellow shop fronts all benefit? (Actually they do slightly, but not to the same extent as leaves in my opinion.)
Next answer is that wet ground allows plant life to get at the nutrients in the ground more effectively thereby improving the health of the organism. Probably true, but the effect of the rain is too immediate for me to be convinced by it. Similarly the response that the rain water contains nitrogen that can be absorbed into the leaves.
Then there is the answer that the hairs and other surface imperfections of the leaf have less effect on scattering light when it’s wet so more of the leaf surface is reflected. Interesting, but I don’t see the logic. Wet surfaces are more reflective generally but don’t all have the green glow.
Personally I think it may be a combination of all of these factors coupled with something to do with light wavelengths of green colours having more contrast in darker skies, but I’m no scientist so have no knowledge or evidence upon which to base such an assertion.