Unfortunately cannabis plants wont absorb much, if any nutrients in the last week or two of flower, this is the time to flush with pure water, for most people.
If you want to stay organic, I would lookup a local supply of blood and bonemeal and amend your growing area with that. There is alot of information online about organic amendments but those two are a solid start.
Looking into how cannabis plants process which nutrient at which time and ph saved me alot of headache.
Happy growing.