I find the best supplement is compost teas,it gives small amounts of fertilizer,but the main thing it does is introduce good bacteria and fungi depending on what recipe you come up with.
the. Fungi and bacteria will in turn 'consume' the organic material in the soil and 'poop' out the processed nutrients ready for your plants.
some good recipes for tea's(5 gallon pail)
this is a fungi dominated tea(not great for pot plants but my spruce trees love it)
2 handfuls mushroom compost,
1 scoop botanicare ZHO/or other fungi brand
one scoop earthworm castings
brew in a 5 gallon pail with the ingredients in a burlap sack,or panti hoes,put a airstone in the bag,and one in the pail.
add unsulphured molassas,or cane sugar.brew for 12-24 hours,water it down 50/50 and use it quickly.
Of course we know pot is a bacterial dominated plant so here is a bacterial dominated tea.
2 handfuls earthworm castings
,40ml botanicare aqua shield/or GH Alaskan humus
and if you want add a little fungi(ZHO or mushroom spores/mushroom compost)
here is a even mix of bacteria and fungi in a tea
i did not make this recipe,I took it from another thread on this forum(I believe it's something like"cure to rootrot"or brownslime)
2 handfuls earthworm castings,
40ml botanicare aqua shield/ or GH Alaskan humus,
1 scoop botanicare ZHO/or mushroom spore blend from (fungi.com I believe)
1-2 tbs unsulphured molassas or cane sugar.
any one of these teas can have bat guano,kelp meal,neem meal,alfalfa meal,rock phosphate,glacial rock dust added with no bad effects.
on a side note the rock minerals have a smaller effect than the meal's in teas because they take so long to break down.
once you get the hang of organics you can start using bat guano teas to fix deficiencies in plants really easily
sorry for my 'simple' explanations,but I want someone that doesn't know anything about organics to be able to follow along