nice post, you really don't even need a p/k boost. another MJ forum myth.
yeah its dependant on the soil you use..a well amended soil done right should be able to go the entire grow with 0 suplimentals. but say you start off in something like pro-mix amended with EWC, the EWC will carry you through a while but the soil will start going blank towards the middle of flower and you will need something to carry the rest of the way.
either way, plants NEED nutrition!! the Myth is that every medium needs suplimets when its not true, the key is to learn your soil and learn how to read your plants. if you have nice healthy plants then the need for supliments is not there but if you start seeing deficiencies you need to be able to spot them and add what is needed, and only what is needed.
I will admit that using suplimental fertilizers done the right way will keep the need to be able to read you plant away as they will always have it. but with adding come many more issues. most people don't realize it but every time you add something to the medium your adding a PH buffer of some form, you can PH your water all you want but if you continue to add buffers that are not being used the PH will change over time causing issues. if you amend a soil properly (or pick a pre amended potting soil) your only adding water so those buffers stay out and your PH usually maintains.
there are lots of published books out there, I would suggest getting one or two of them, one that is written on growing cannabis and another that focuses on the style growing your doing..
so a hydroponics book if your growing hydro or a organic gardening book if you want to grow organics.
books are good because they usually are written by someone who knows what they are talking about..the unfortunate problem with forums and especially forums that deal with growing cannabis is that they are largely populated with people who are stoned (no offense) and when your stoned you get ideas that are brilliant (especially to someone who is stoned as well) and then they circulate..the biggest problem is stoners tend to overthink things that are normally simple and don't need overthinking. again im not trying to insult anyone for being stoned..i just think the theorycrafting on horticulture should be done in a lab and not a stoners bedroom while watching weeds.