Comfrey tea is rich in nitrogen and potassium; it is a nutritious side-dressing for fruiting vegetables. Tomatoes, peppers, cucumbers, and berries use nitrogen to support leaf growth and potassium to promote flowers and fruit. The nitrogen-phosphorus-potassium (NPK) ratio of dried comfrey leaves is 1.8-0.5-5.3; comfrey also contains calcium.
Comfrey is a perennial herb that is easily grown in average soil; it will thrive in sun or partial shade. Russian comfrey (Symphytum x uplandicum) is the best choice but there are other comfrey varieties that will work. Plant comfrey in spring or autumn and let the plant become established before harvesting leaves for tea making the following year. Space comfrey plants at least 30 inches apart; mature plants will grow to about 2 feet tall from a basal leaf cluster. Leaves are best harvested just as flower stalks rise. Comfrey can be invasive; it is best to grow comfrey where it can remain undisturbed for as long as 20 years (a comfrey corner of the garden).
Comfrey Tea Recipe
• Harvest comfrey leaves from established plants; wear gloves, long sleeves, long pants and shoes: comfrey leaves can irritate the skin. From an established plant you can get 3 or 4 cut-and-come-again harvests each year.
• Use a bucket or other container to make comfrey tea. Fill the container about half to three-quarters full of comfrey leaves. Place a wooden block or brick on top of the leaves to press them down. Fill the container with water and place a lid on top.
• Comfrey leaves are quick to rot. The water will turn into a dark, foul-smelling manure tea in about 20 days and will brew darker and darker if left for as long as 6 weeks. The lid will keep flies out.
• Draw the tea from the container and dilute it by at least 50 percent; some gardeners dilute comfrey tea by 10 times before side-dressing plants. If you put a tap at the bottom of the container, you can add leaves and water to the top to keep new tea brewing for months.
• Apply comfrey tea as a side-dressing or foliar spray; comfrey tea is potent so let a little go a long way. Use comfrey tea as a side dressing every 10 to 14 days from flower set through the development of fruits. As a foliar spray, quit applying comfrey tea at least a month before harvest. Comfrey tea diluted is an excellent fertilizer for container vegetables. (Comfrey tea as a foliar spray has been found to slow the growth of powdery mildew spores on plant leaves.)
Comfrey Manure Mulch
Wilted comfrey leaves can be used as sheet-mulch manure. Place two or three layers around the base of plants or bury them in the soil 2 inches deep to the side of crops including tomatoes, peppers, potatoes, currants, gooseberries, and fruit trees. The high nitrogen and potassium content of comfrey leaves will be almost immediately available to crops. (High nitrogen fertilizers are not a good match for leafy crops such as lettuce and spinach; the nitrogen boost may cause them to go to seed prematurely. As well, high potassium fertilizers are not a good match for rooting crops such as carrots.)
Comfrey Liquid Fertilizer
To make a comfrey fertilizer concentrate, pack comfrey leaves tightly into a container, weigh them down, cover, and let them rot. In about 3 weeks, you will have a liquid fertilizer concentrate that can be mixed with 15 parts water to 1 part comfrey goo and used as a fertilizer side dressing.
Comfrey Compost Activator
Comfrey leaves can also be used as a compost activator in compost piles rich in brown carbon material. Place a layer or two of comfrey leaves on the top of the compost pile and sprinkle garden soil on top. The quick rotting comfrey leaves rich in nitrogen will work with bacteria and soil organisms to speed the composting of dried leaves and other high carbon materials.