A comment on a previous Rosemary post suggested I try to incorporate sand into the potting mix. Upon more research, adding sand to the mix improves drainage and actually tries to mimic the natural environment of the Rosemary somewhere in the Mediterranean. This video provides a recipe for it. But i had to tweak it a bit given that I only had 1 kg of sand.
Because the sand is courser than soil or compost it is not easily compacted. This will allow spaces in between the granules to let the water drain through and also allow oxygen to reach the roots. Hopefully the Rosemary gets better with this mix. I also intend to try this mix on a batch of cilantro.