Comfrey Leaves (Symphytum officinale) I have a small patch of comfrey in my community garden area and find it invaluable. I cut the leaves regularly, which keeps the plants under control. Added to the compost heap, they work as activators and as valuable sources of potassium and phosphate. You can also put the leaves into water to create liquid feed. Every productive garden should have at least one comfrey plant. heirloomgardener