in my local grocery and hardware stores, they rent out these industrial-type steam carpet cleaners with special solution....maybe try that? might be cheaper than hiring a professional carpet cleaning service....
This happened to me with a 3 foot tree in a pot, and cleanup was really simple. I put a towel over the whole mess (after having scooped up as much as I could with my hands) then let it stay that was for a few days until the dirt had all dried up. Then I was able to vacuum it all up in one fell swoop.