reusung soil

i was wondering about reusing soil is it possible? how long should it sit before reusing?

How can you not reuse soil? Earth has grown millions of plants in the same soil for millions of years.....

i've been using MG organic for a while, and when I pot, I use half new stuff, and half soil from an old grow. Seems to be fine for me, just make sure you give your seedlings food early enough, because I flush my plants at the end of flower, so I'm sure all the nutes are leeched from the soil. And when I mix it with new stuff, it is going to have a lot less nutes in it.