You know how it goes, April showers bring May flowers...pretty it up with images akin to the Morton salt girl visiting the Netherlands during tulip blooming season, but the Midwest rain/mud season of Spring is tough to endure. Damp insults, adding to the injuries of cold, wet shoes, socks, feet...many people find their weather patience limits maxed out with a contempt deeper than the disdain for winter.
It's good for the plants, we tell ourselves. And generally, in an indirect way, you could say that.
April showers bring May flowers.
Except, it's not so much the showers as lightning. Oh, and not so much the flowers directly, but rather all the green parts of the plants (and technically, you need those green parts to get the flowers, but if we're splitting cilia...).
It's the lightning that makes the landscape, and yards, and gardens so green, providing a free fertilizer by zapping nitrogen molecules in our atmosphere. This air-version of nitrogen hangs out as two nitrogen atoms bonded together aka N2, and lightning undoes this bond, THEN rebonds the nitrogen atoms to oxygen (NO3).
These NO3 molecules are called nitrates. Nitrates are fertilizer because it's these nitrogen molecules that plants can use - plants cannot use the nitrogen in the atmosphere under "regular" conditions (the N2), and the ecosystem has several ways of cycling the N2 in the air to be NO3 and available for plants to use.
That's good, because nitrogen is a major player in the chlorophyll molecule, central to the molecule to be exact. So lots of available NO3 means lots of green!
Nitrogen is represented by the blue atoms.
However, the non-lightning ways are notably slower (e.g. plants and animals have to live and die and decompose) than the other two main ways of getting nitrates to plants: lightning and fertilizing, both directly apply nitrates to the soil matrix making it available to plants.
Hence rain showers with lightning is essentially free fertilizer.
For more about the nitrogen cycle or to have it explained in a short 5 minute video, see this NOVA: Earth From Space excerpt (and visit the page for resources to use in the classroom!).