Hi Edmick,
I would recommend moving them to a bigger pot, to allow for room at the top of the pot. Then I would top dress with a premium compost and then either leaves, straw, chips or some other mulch to keep the moisture in
I used "organic" fertilizers in the past but they were no good.
The other option is the opposite and using the hydro nutrients in a DWC set-up and ditching the "soil"