'They are called idioms in a sense because some of us can't help but feel uneducated when we cannot figure out what they mean or why that phrase would come to mean what it does.'
What? That is not why they are called idioms.
You also misused or misunderstood the two idioms you used, and also listed the internet one, which isn't an idiom.
There is an Indian perfume base called Mitti Attar which tries to replicate this smell. It's like damp moss at first scent, then develops into rain on hot sand. It is entrancing. Proper Mitti Attar sells for thousands and takes years to make.
As a father of multiple children, don't bother. It'll get dirty with debris and insects and grass with kids using it long before your filter would be needed. Just empty and refill when it gets dirty.
I've only ever used 2 of these. I'm a greedy sloth.