You can use synthetic and non-synthetic together, but begging for disaster. Also with non-synthetic ammendments most times need microbial life to break those ammendments down to a point the roots can uptake them...the nature of well nature. Synthetic Ferts kill microbial life, FACT.
I am not here to argue chem and organic terminology in this thread. I just didn't want him doing like a lot of others new to the game of custom mix non-synthetic mediums by adding a bunch of stuff in conjunction of an improper liquid fert regimen which almost always end up with torched plants and too many ingredients to figure out what did what.
This is what makes people abandon this style of growing...way to easy to get carried away.
I can be "hardcore" about using the exact right term. but everyone here recognizes when I say chem...I mean "synthesized ferts from mined resources"
not "non-synthesized ferts from readily renewable resources" not billion years renewable.
To say synthetic and non-synthetic can't be used together is not true. but there is a reason why its not recommended.
If he uses pre-mix non synthetic or semi-synthetic liquid ferts (fox farms), blood meal bone meal and guanos aren't really needed anymore, but kelp, greensand, worm castings would be good . If using like Gen Hydro's maxi line then just dirt perlite and lime is all that is needed. Adding further amendments can cause major problems within the medium,.
He asked a question leaving too many variables.
active amendments in 99% of non-synthetic (OMRI cert. organic) gardening
manure
compost
guano
ground crab shells and stuff like that
worm castings
kelp
and the list goes on and on and on each one microbial life can thrive in and utilize.
inactive amendments would be
perlite
vermiculite
river rock
stuff that is not actively used by microbial life. but does not make it OMRI unacceptable.
synthesized amendments (does not meet OMRI cert.) create a medium in which microbial life cannot exist and thrive in any amount that would be beneficial to plants. Can't say ALL are dead as they find life at the bottom of the sea with no light and sulfur toxicity with temps that life should not be present. Just not thriving to do the plant any good.