I live in a townhouse with a private yard that is completely enclosed with concrete. On both sides of the private yard are planters built into the concrete. My problem is that whenever it rains, hundreds of worms come up out of the soil and throw themselves onto the concrete floor where they die. I find myself having to scrape them off the ground quite often in the rainy season. The planters do have drainage, but I think it may not be enough.
I researched toxins to reduce the worm population, but they seem dangerous. If it was a few (or even a few dozen) worms coming out of the soil, I wouldn't mind so much, but I kid you not there are hundreds.
Any ideas on how to address the situation? Totally new to gardening so please excuse my ignorance.