perlite?

can you plant in just perlite? or is it better to add it to soil?

Ya can. a just have to water often and provide all the nutes to the plant.

what nutes would i need?

https://www.rollitup.org/general-marijuana-growing/59705-hempy-collective.html

check out the hempy bucket method.

i have MG perlite with houseplant food which probly wont do anything. will 18-18-21 work? thats the closest i could find to 20-20-20

can you plant in just perlite?
Yes.

or is it better to add it to soil?
That depends on what you mean by "better"!
I'm sure there is a whole laundry list of "Pro's & Con's" for using Perlite by itself (as the only medium), here are just a few:

Pro's:
1. It is virtually sterilized.
2. Retains water well, when "dry". Retains oxygen well, when "wet".
3. It is virtually inert, so it lends itself well to hydroponic type systems/conditions.

con's
1. It is virtually inert, so it requires hydroponic type systems/conditions. As well as the added knowledge to make it all work!
2. It offers little support to mechanically anchor the plant in a proper manner.

yes,the only drawback to using perlite is that the roots wont have much to anchor themselvces to..so I suggest starting the plants off ion either rockwool or rapid rooter plugs....but yes you can grow plants in just perlite..also,youll have to water MUCH ,more frequently than say coco coir,or rockwool...perlite dries much faster than all other mediums..so if youre growing in h.i.ds the perlite will dry out too fast..thats why more people dont use perlkite in hydro..they use rockwool or coco coir..