Many years ago, comfrey was grown as a popular medicinal herb. Reaching nearly five feet tall, with large, prickly leaves beneath hanging clusters of colorful, bell-shaped flowers, the true benefits of comfrey lie in the plant’s roots’ ability to break up tough clay soils, and its nitrogen-heavy leaves’ use as a nutrient-dense fertilizer. However, for years the herb was also prized for its supposed healing abilities. Before we tell you anything else we need to let you know that comfrey may no longer be considered safe for internal consumption by humans or animals. However, many people still use comfrey medicinally in topical skin preparations. These include, pain relieving salves and other topical treatments, including us.
Additionally, adding comfrey to your garden will attract “predatory insects”. These are the types of beneficial bugs that will protect your plants from pests that they are otherwise susceptible to. Moreover, if you allow that comfrey crops to bloom, the flowers are beautifully colored cream, pink, and blue flowers. All of which attract pollinators, which we all know is a much needed benefit for every garden.
Ready to start growing some comfrey? Keep on reading to find out everything you need to know to start!
When and Where You Should Grow Comfrey
Comfrey can be planted any time when the soil is not frozen, and seedlings are not facing immediate danger of frost. Planting is preferable in the Spring or Fall seasons. If planting in the Fall, try to get your seedlings or transplants in the ground early enough that roots will have time to establish before the first frost. Remember, essentially comfrey is a weed, and as such is quite hearty. Freezing temperatures will not kill comfrey roots.
Be sure to pick a spot for your comfrey plant that receives medium to full sunlight, and which has adequate drainage. If necessary, grow your comfrey in a container if you are concerned about the plant’s propensity to spread. Do not plant comfrey anywhere where you intend to cultivate other crops, as any broken roots will result in new comfrey springing up all over your garden.
One of the most important things to understand about comfrey is that once established, it is nearly impossible to get rid of. The first step in preparing to grow comfrey is selecting the proper placement in your garden. The second step is to determine which type of comfrey you wish to plant.
Understanding Seed Germination of Comfrey
Comfrey requires a winter “chilling period” in order to germinate, and it is very common to wait two years after sowing seed before seeing signs of germination. It’s for this reason that most gardeners forego starting their comfrey by seed. Instead, they choose to start with one of the widely available alternatives, such as a live root cutting. A great majority of gardeners also choose to begin their comfrey crops with a live root cutting or transplant due to the relative ease and simplicity of this method over germinating seeds. Check your local farms and nurseries for the best options close to you!
One of the great benefits to growing comfrey is the freedom it provides. You may choose to begin growing your comfrey indoors or outside, and you may begin with seed or a live root cutting or transplant. Regardless of the method you prefer, you can expect your comfrey crop to thrive in most growing conditions.
Comfrey prefers clay soil but will flourish in a variety of settings provided it receives plenty of moisture. Prior to planting your comfrey, follow the same general recommendations you would for the preparation of any quality vegetable bed or garden. Carefully weed the existing ground. Although comfrey’s roots will eventually overwhelm other weeds, it can take a few years to become established. Comfrey grows best in soil with a pH of 6.0-7.0, but as mentioned, will grow under a variety of conditions. Add any needed amendments to the soil and compost prior to planting your comfrey in order to achieve your ideal growing environment.
Additionally, if you are planting your comfrey near trees or shrubs, consider digging a trench into the portion of the soil that will separate the intended comfrey patch from the trees or shrubs. The root system of the other plants can detect the recent fertilization present in the soil and migrate into the comfrey bed unless a barrier is present.
One other thing you may want to keep in mind when picking a spot for your comfrey is its ability to speed up composting. Since comfrey’s six-foot long roots pull tons of nitrogen, phosphorus, and potassium from the soil. It makes a wonderful choice for decomposition into organic matter as well. According to researchers in British Columbia, the NPK rating of dried comfrey leaves is 1.8-0.5-5.3. For comparison, the NPK (Nitrogen, Phosphorus, Potassium) rating for kelp meal (another highly recommended soil amendment) is 1.0-0.5-2.5. Because of all the nutrients the plant uptakes, it becomes easy to see why comfrey is also often used as a compost accelerator.
Starting Comfrey from Seed
If choosing to start your comfrey from seed, it is critical that you select “true” or “common” comfrey. These are the seeds which are capable of reproducing. The other variety of comfrey, “Russian comfrey”, is sterile, which means that the seeds do not grow.
Now, the first thing you need to do in order to germinate your comfrey seeds is to break their dormancy cycle. This can be achieved through “stratification,” or the process of mimicking cold, moist winter conditions. The following is the stratification process recommended by Nantahala Farm:
- Place seeds in moist sand, vermiculite, coconut coir, potting soil, soilless potting mix, or paper towel. After this, place it in a baggie, cloth bag, or glass jar with lid. You will want to avoid placing in a paper towel if you can, as it is sterile and does not contain endogenous growth hormones that encourage germination. Additionally, don’t just use peat moss alone as it is too acidic.
- To assist your seeds in germinating, add a little kelp (seaweed) to the medium. Since kelp has naturally occurring growth hormones it will help seeds germinate. Additionally, it can help prevent damping off.
- Now, simply place the bag or jar in your refrigerator. You will want to keep them in there for the next 30 days (up to 60 days maximum). The reason you are doing this is to break the dormancy of the seeds by creating winter-like conditions. Do not put them in your freezer when moist though.
- After this, you will want to plant outside once the soil temperature is between 68-80 degrees Fahrenheit. Just remember, germination results are better when first planted in a warm greenhouse or sunny window.
- While the seed is still thinking about sprouting try to keep soil temperature between 68-80 degrees Fahrenheit. If needed, you can use supplemental heat such as a heat lamp or horticulture heat pads. You will want to adjust the thermostat for 70 to 80 degrees.
- Since we’ve now created the perfect environment for the seeds to sprout, you should seed them germinate in 10-15 days.
If starting seedlings inside and planning to transfer outdoors, wait to transfer until after the seedlings have been growing indoors for a few months. Then, you will gradually harden them to external conditions over the course of a couple of weeks before planting outside.
Of course, remember that comfrey may also be kept in pots outside and cultivated as desired. This can help prevent any spread of the plant’s deep root system, while still providing your garden with the many benefits of growing the herb.
Planting Root Cuttings or Transplants
While single comfrey transplants are available for purchase, live root cuttings are by far the most common and economical way to grow multiple comfrey plants or to begin a comfrey bed. Most often, you will get root cuttings that are 2-6 inches long roots from the comfrey plant.
To plant the cuttings, you place them horizontally about 2-6 inches deeper. Just keep in mind what kind of soil you have. The more clay, the shallower you can plant the cuttings and the more sand, the deeper you’ll want to plant.
Additionally, root cuttings and transplants are usually spaced about three feet apart.
To be clear, live root cuttings are pieces of living root that are planted entirely below the soil, at least two inches deep, in the hope they will create a new root system and generate a new plant. Transplants are young, small, whole plants that are transferred to a new, permanent location. Transplants are buried up to the crown only.
When preparing to plant root cuttings or transplants, soil preparation remains the same as previously described. It is recommended to provide compost both beneath the cutting at the time of transplant, as well as around the base of the plant. You can also add worm castings to the base of the plant for added nutrients.
While your plants likely grew a decent amount this first year, it is advised to not harvest anything from the plant in this first year. Since comfrey relies heavily on its deep root system, simply cut the plant’s leaves back and allow it to continue forming a strong root system.
How to Take Root Cuttings
Watch the below video to learn how to take root cuttings from a mature comfrey plant.
Watering and Mulching Requirements
Comfrey is known for its large taproot, which is a hardy, central root from which all other roots sprout laterally. Because of the depth to which comfrey’s tap root reaches, it is known to be a drought-tolerant crop. That said, when first planting, your comfrey plant will need frequent watering in order to become established. Once the tap root has taken hold, regular watering will help your comfrey crop thrive. Always remember to water and mulch after harvesting your comfrey, as well.
Comfrey is a nitrogen-hungry plant. It’s penetrating roots are happy to take advantage of any fertilizer provided. Moreover, one of the best options for feeding your comfrey is the comfrey itself! Mulch around your comfrey crop with the comfrey’s own leaves to help return some of that necessary nitrogen to the soil. Another option is to maintain a thick layer of grass around the comfrey bed. However, even without additional fertilization, once established, comfrey plants are notoriously difficult to eradicate. Regular feeding is not particularly necessary to maintain this crop, though mulching with a rich organic matter will certainly result in even healthier plants and more plentiful harvests.
When considering the planning of a permaculture garden, companion planting is always one of our primary concerns. It is here where comfrey really shines. Comfrey is an excellent companion to nearly every plant, as mature, dried comfrey leaves can become an excellent mulch, tea, or fermented plant juice. Comfrey is even an excellent mulch for itself!
However, comfrey will often take over wherever it is planted. In order to solve this problem, consider planting comfrey in a container or creating a solid barrier to prevent it from spreading. Also, as a perennial, though comfrey will die back in the winter, you can expect it to return even more generously each spring. Therefore, this crop has no rotation considerations.
A prime example of maximizing comfrey as a companion in the garden can be found when utilizing it to enhance your organic cannabis crops. We know that comfrey leaves are nutrient-dense, but did you know that they are one of the few naturally-occurring sources of potassium? By feeding your cannabis crops comfrey fertilizer throughout the flower cycle, you’ll be giving your plants the boost they need and want! Seriously, mix it up in a tea, ferment it or just mulch with it, your plants will thank you for it!
Along with potassium, comfrey is also a strong source of nitrogen, phosphorus, and calcium. The high levels of nitrogen make the leaves an excellent bio-activator for your compost, speeding up the time it takes for your compost pile to become usable compost. Additionally, cutting off the leaves in the fall and mixing pieces into the top layer of your soil will allow the leaves to release their nutrients in time for spring planting.
Harvesting and Using Comfrey
Comfrey is a perennial plant, meaning that is it expected to live beyond two years. Comfrey blooms once every year between late spring and early summer, and unlike a shrub, can be expected to die back in the winter. It is certified to grow as a perennial in the United States in USDA Hardiness Zones 4-9. Click here to find your USDA Hardiness Zone, or consult this map.
If you are only growing comfrey for the leaves, you can begin harvesting when the plant is about two feet tall. Cut the leaves back to within a few inches of the crown. The leaves can be dried and turned into a mulch, tea, or fermented plant juice for your other crops. Comfrey is widely known to be a highly beneficial soil amendment for almost every crop. Some farmers have also been known to use comfrey as an inexpensive and well-tolerated feed for certain ruminants, chickens, rabbits, and pigs. However, the safety of comfrey among livestock is contested.
If you would like for your comfrey crop to bloom flowers, you’ll want to wait before you harvest. The best time to trim the leaves for compost and tea is before the plant flowers. Of course, if you want the colorful blooms in your garden, you will need to wait for them to arrive. Regardless, remember to only harvest the leaves for your compost or tea-making, as the flowering stems have the propensity to take root if transferred elsewhere in your garden.
Additionally, the dark green leaves of comfrey are covered in small, prickly hairs which are irritating to the skin of some people. If you find this is the case, wear gloves when handling the plant, or beforehand as a precautionary measure.
Choosing the Best Comfrey Variety for your Garden
The two types of comfrey you are most likely to encounter are:
- Russian Comfrey
- Common or True Comfrey.
The primary difference is that Russian Comfrey (specifically the “Bocking #4 or #14” varieties most commonly available) is sterile, meaning that it does not “self-seed.” Conversely, the “True” or “Common” varieties of comfrey will self-seed and are said to be less vigorous growers, but with deeper colored flowers. At about three feet tall, True comfrey is smaller than Russian comfrey.
Most home gardeners greatly prefer the sterile, Russian varieties of comfrey. The advantage of these varieties over “true” or “common” comfrey is that you needn’t worry about the plant’s seeds spreading around your garden, for they will not germinate.
In addition, the Russian (Bocking #4 or #14) varieties of comfrey are larger and the blooms are said to be more brightly colored than the “true” or “common” variety, which is known for smaller plants with more richly colored darker blooms. Despite these differences, all types of comfrey offer the same nutrient benefits when used as compost or other type of amendment for any of your garden
Additional Tips for Growing Comfrey
- When planting comfrey, ensure you are selecting the sterile “Russian” (Bocking #4 or #14) cultivars. These plants rarely produce seed, and the seeds they do produce will not germinate, so you have a much lower risk of the plant taking over your garden. On the other hand, if you wish to begin your comfrey from seed, you must be sure to purchase “True” or “Common” comfrey seeds, which are capable of germination.
- Comfrey may be difficult to eradicate due to its long taproot. This central portion of the comfrey root structure is responsible for the resiliency of the crop. It can grow up to six feet into the ground! This is also how the comfrey leaves absorb such incredible amounts of nutrients from the soil, as well as how the crop is able to survive frost and mild drought. Each smaller root grows off of this main root laterally. However, if the ground around the comfrey is tilled and any of these roots are cut, that root cutting is then capable of starting a brand new plant, with its own taproot. For this reason, it is important not to cultivate the area around where the comfrey is planted.
- In order to make comfrey tea, place torn up comfrey leaves into a gallon-sized bucket. Fill the bucket about halfway with leaves and weigh the leaves down with something heavy, like a brick. Fill the bucket with water and set it somewhere far away from your home, as it will become very smelly. In about a month the leaves can be strained from the mixture and used as a dressing in your garden. The remaining tea should be diluted with water and applied according to your plants’ needs. Another method you may prefer is to skip the water and instead allow the leaves to decompose into an extract on their own. This extract should be diluted with water 1:15, then used in the same way as the tea.