Tie the branches of the large Rormarinus officinalis together with twine to keep them out of the way when repotting.
Combine the soil ingredients: 2 parts cactus potting mix, 1 part perlite and 1 tablespoon of dolomitic lime per gallon of the two other ingredients. Pour the mixture into the new pot until it is half full.
Remove the Rosmarinus officinalis from its current pot. Depending upon the size of the shrub and the length of time it has been growing in this pot, this task may be challenging. Lay the pot on its side and slide the shrub out. If it is stuck, try rapping around the outside of the pot sharply with your hands to loosen the roots stuck to the inside. If that fails to loosen the plant, run a hose into the pot, while it is lying on its side, to wash the soil from the rootball.
Place the rosemary's roots on top of the soil mix in the new pot and check to make sure it sits at the same depth it did in the old pot. If not, add or remove some planting mix until it does.
Finish filling the pot with the mix, patting it down periodically with your hands to remove air pockets. Fill the new container to within 1 inch of the rim.
Water the newly potted Rosmarinus officinalis slowly until water seeps from the bottom of the pot. After it drains, water again, slowly, to ensure that the soil and rootball are completely wet. Use your hands to press the soil down around the base of the plant.