Place the leaves and other above ground plant parts in a bucket that has a lid or another large container that can be similarly sealed.
Pour hot to boiling water into the container, making sure that all of the plant parts are covered.
Place a brick or similarly heavy item onto the plant parts to keep them from floating to the surface of the water.
Place the lid on the container and allow the mixture to steep and “rot down” for about six weeks.
Strain away any debris left in the water and use the comfrey tea to pour or squirt around plants in the garden.