But to be honest i wouldnt add any untill you get a bag of perlite. Dude you would be surprised how cheap a big bag of perlite can be at hydro store. Cheap enouhh you could probably scrounge enough from quarters laying around the house. Worm castings have zero perlite added to it. The fox farms comes with not nearly enough so if your top dressing fox farms or roots organics with worm casts , id make sure to mix perlite and worm cast together first then top dress it. Becauae if you didnt the worm castings would hold moisture around for way too long and on top soil is generally where fungus gnats thrive so it's best to have a good dry top layer