I have made some liquid plant feed from comfrey leaves and water. Is this suitable for rosemary? (I know it is good for tomatoes)
Should Rosemary Plants Be Fed/Given Compost?
Certified GKH Gardening Expert
I would not use fertilizer on rosemary (or most herbs). The reason being is that fertilizer will cause rapid growth and the plant cannot keep up with producing the chemicals that create the flavor at the same rate as the growth. It results in a less flavorful leaf on the plant which means a poorer quality herb for cooking. However, this does not mean you cannot do so. It is entirely up to you and if you're not using the rosemary for cooking, then it really shouldn't matter anyway. If you decide to fertilize, the mix your made should be fine.