I am planning to grow some comfrey at home, and it seems like the Bocking No.14 hybrid is ideal - the highest amounts of alantoin, and it is not as invasive as other varieties, being sterile. It may also have lower levels of the alkaloids, although this is not a great concern for me, as I'll probably use it for composting most of the time. I'm wondering if there's any reason to choose another variety, though. Since we have a small yard, having this stuff seed everywhere and spread could be a problem, although it could be useful in the back yard where there is a bunch of sand remaining from the previous owners' pool - maybe the comfrey's tap root could help rebuild the soil by pulling nutrients up and then being used as mulch/compost?
So I guess what I'm wondering is: are there any specific concerns about using a hybrid for medicinal use?
This website seems to address most of my questions:
_http://www.nantahala-farm.com/comfrey-root-bocking-14-s.shtml
[Edit:]
I just ordered 2 root cuttings of Bocking No. 14 from the above website, as it seemed to be a good value and comes with a comfrey growing guide. I could get another variety eventually if there's a need.
So I guess what I'm wondering is: are there any specific concerns about using a hybrid for medicinal use?
This website seems to address most of my questions:
_http://www.nantahala-farm.com/comfrey-root-bocking-14-s.shtml
Traits of All Russian Comfrey Cultivars
All types of Russian Comfrey (cultivars Bocking No. 1 through Bocking No. 21) are botanically known as "Symphytum × uplandicum" or "Symphytum x uplandica". They all are a cross (natural hybrid, not GMO) between rough comfrey and common comfrey. They grow to 4 feet tall including the flower stalk.
Russian comfrey has purple, magenta-pink, red or blue (that fade to pink) flowers. The seeds are not viable (will not grow). It has to be reproduced by root and crown cuttings.
Russian Comfrey is very hardy. It can withstand temperatures as low as -15 degrees. Good in USDA Zones 3-9.
The powerful roots of Russian Comfrey Bocking #4 go down 6-8 feet. Bocking #14 roots go down 8-10 feet. Both are good plants to use to break up hard soil.
High in Protein and Biomass
Both Russian Comfreys produce up to 100-120 tons per acre of leaf biomass (recently cut) per year. This is about 12.4 tons of dried comfrey leaf per acre. This is 3 times the amount that True Comfrey produces. Alfalfa yields 18 tons per acre (just cut). Corn is 25 tons per acre before it is dried. Pasture grass is 25 tons an acre.
The protein amount in dried comfrey is 20-30%. Most beans (legumes) are around 8-9%. Soybeans are around 17%.
All comfrey (Russian and True) contains Pyrrolizidine Alkaloids (PAs) and can be toxic if used internally by people. It is hard on your liver. Small young leaves have higher concentrations than larger, older leaves. The PAs in roots are concentrated more in small young roots. Roots contain more than leaves. Leaves have about 0.06% alkaloids. Roots have about 0.2-0.4%.
Bocking #4 and #14 Are Similar
Both Bocking #4 and #14 can be used as garden fertilizer, compost activator, mulch, or be fed to animals as fodder. Both reduce transplant shock of plants.
Bocking #14 is more frequently used as a garden fertilizer. Bocking #4 is used more as an animal fodder. It is usually preferred by animals over Bocking #14. Either variety can fulfill your needs if you only want to grow one type.
Comfrey has been grown and used as an healing herb since 400 BC. True comfrey (Symphytum officinale) is usually suggested as the best one to use internally medicinally though caution is advised. Never use a lot of it internally.
There are studies that seem to indicate that Russian Comfrey has fewer of the toxic alkaloids than True Comfrey. Externally all comfrey (True or Russian) is good to use. Contact your doctor or herbalist.
Bocking No. 14 and Your Garden
Bocking #14 is the preferred type when used as a garden fertilizer.
Leaves are wilted and then placed in a hole or trench to act as nutrition for whatever is planted in the hole such as potatoes. It's stems are smaller and thinner than Bocking #4. So they wilt easily and are not likely to start sprouting into a comfrey plant when covered with dirt.
Another way to use it is by making liquid fertilizer or compost tea. You put about 5 pounds of comfrey leaves in 7 gallons of water. If you want a lot of fertilizer, use a 55 gallon barrel. Use a proportional amount of leaves. Cover with a lid and let sit for 4-6 weeks. The liquid is used to fertilize your plants.
The Book: "Comfrey Report"
From the book "Comfrey Report: The Story of the World's Fastest Protein Builder and Herbal Healer" by Lawrence D. Hills:
"There are two commercial strains-- the Webster and Stephenson. Bocking No. 14- This is the dominant in the Stephenson strain, 80% to 90%. The flower stems are slender and frequent and are entirely wingless. The flowers are Imperial Purple 33/3 fading to Lilac Purple 031/3. The leaves are pointed, slightly serrated at the edges and vary in proportion from 5 to 12 and 3 to 6."
The photo to the left is Lawrence Hills who wrote several comfrey books that are the authoritative works on the subject. He is the person who created the natural hybrid Russian Comfrey, Bocking #1-#21. He is next to a comfrey plant.
Comparing Bocking #14 to #4
Allantoin is the healing chemical found in all comfrey. It stimulates cell growth and repair. It has been used by herbalists for 2000 years. It is used in skin care products. It is found in the roots and in the leaves.
In Bocking #14 leaves allantoin is 0.44%. In Bocking #4 leaves it is 0.34%. In True Comfrey (S. Officinale) it is 0.30%. Allantoin heals digestive problems so comfrey leaves have been used for decades to reduce scouring (diarrhea) in horses, cows and pigs.
Russian Comfrey is high in potash (potassium). Leaves of Bocking #14 are 7.09% potash. Bocking #4 is 5.04%. True Comfrey (Symphytum officinale) has 5.3% potash. Wilted comfrey has more than twice as much potash as farm manure and 30% more than compost. The Nitrogen-Phosphorus-Potassium (NPK) ratio of True Comfrey is 1.80-0.50-5.30.
More Bocking Comparisons
All comfrey contains vitamin B12, one of the few plants to have it. Most vitamin B12 is found in animal products such as liver, eggs and milk. Leaves of Bocking #14 have 4.4 nanograms of B12 per gram. Bocking #4 has 11.6 per gram (more than double #4). Dried yeast has 1.1 per gram.
Bocking #14 Comfrey is more rust resistant.
Bocking #4 is more drought resistant than #14 because it has deeper roots.
[Edit:]
I just ordered 2 root cuttings of Bocking No. 14 from the above website, as it seemed to be a good value and comes with a comfrey growing guide. I could get another variety eventually if there's a need.