White widow auto , first grow ever

It is depending on your compost , I am personally making some grass compost and I assure you that you can grow straight into it without mixing with soil or anything else. I think that you need to mix your compost with soil if your compost is very rich or if the compost structure isn't good enough to plant something inside. Now you said you've put 30% coco and 10% perlite so technically you did mix your compost with 40% different medium so even if it's not a compost/soil mix is a compost/coco/perlite mix so the advice to mix your compost is followed here