Comfrey as Fertilizer, and Animal Feed

One of my several comfrey plants

I grow a lot of comfrey and it makes a great fertilizer. That's because comfrey is known as a dynamic accumulator, meaning the roots grow very deep (as much as 10 feet) and "mine" nutrients... that is, they bring nutrients up from the sub-soil and into their leaves. Those nutrients then can feed other plants if the comfrey leaves are used as a fertilizer.

Comfrey leaves have twice the nitrogen of composted manure,  about 18 times the potash, and 59 times the amount of phosphorus.

There are several ways to make fertilizer from comfrey leaves. The leaves can be put in water to dissolve, and be used as a fertilizing tea, or mixed with other liquid fertilizers. They can be put in a bucket where they will wilt and then dissolve into a very smelly liquid which can be thinned with 15 parts of water for a foliar feed or a fertilizing tea. You can also add the leaves to a compost pile.

Personally, I like to line trenches with several layers of fresh-cut leaves, cover them with a layer of dirt, and plant potatoes in the trench. I also just lay a few of layers of leaves along the sides of my tomato plants as a feeding mulch.

There are a few other plants that are also dynamic accumulators. The list includes arrowroot, borage, buckwheat, carrot leaves, chicory, clovers, daikon, kelp, lemon balm, marigold, mints, stinging nettle and yarrow. I'm sure there are others but those are the ones I know about. Most of those do not "mine" as deeply as comfrey, though.

Comfrey as Animal Feed

Comfrey is of great value as a feedstock.
 
Apparently pigs love it and will happily consume up to 20lbs a day! The Nihon Agricultural
University in Japan stated that: ‘a noticeable result was the improved health of the pigs
fed on comfrey’ not only from the allantoin, which banished scouring, but better mineral
balance.
 
Comfrey has been successfully fed to a wide range of animals from racehorses through
sheep and cattle to exotic animals such as giraffes.
 
For the homeowner and gardener who may keep poultry, comfrey can provide a
useful and productive addition to the their diet. The simple digestive system of the hen contains no bacteria or stomach enzyme able to digest cellulose so the hen receives no value from high-fiber diets. In fact this is a positive disadvantage because when the crude fiber
content reaches 10% or more, there can be a reduction in the digestibility of carbohydrates. This will cause  a fall in egg yields and delayed maturity even if the rest of the diet is nutritious.
 
Comfrey provides a low fiber, high protein and high mineral feed which can effectively replace some costly concentrates in the poultry diet. Comfrey is best served wilted and shredded, with the fibrous stalks removed to further decrease the fiber. 5 plants per laying hen should provide enough comfrey for feeding purposes.
 
Obviously comfrey is available in winter in most of the US (unless silaged) so should be replaced with other foodstuffs, such as kale or cabbage.