That depends where you are located. You won’t find too much clay in Northern Ontario its all sand. But most soil in Southern Ontario is clay based.
I used to gorilla grow . I’d Dig right down to the clay layer(18-30 inches) apply a wack of gypsum right on the clay, then fill with mix . In the fall all of the monster plants had roots were cemented right into the clay. The following years the your spots will just get deeper.