Comfrey is one of the most-mentioned plants is permaculture circles – known for being a wonderful plant to aid in the circular function of a sustainable, organic garden. But traditional polytunnel gardeners may not always be aware of the benefits of growing comfrey in their gardens and some may even consider some types as weeds.
Comfrey is the common name given to a number of species and hybrids within the Symphytum genus, in the Boraginaceae plant family. Traditionally used in folk medicine, comfrey is also known as knitbone or boneset after one of its old-time herbalism uses. Though today it is not commonly used in any way medicinally, and certainly, internal use is not recommended.
There are many reasons to grow comfrey in your garden, it:
Is good at drawing up specific nutrients from the soil, including from deeper soil layers. The specific balance of nutrients the plant contains and the quantities thereof make this a useful crop to chop and drop, use as mulch, add to your compost heap or use to make a liquid plant feed.
Works as a wildlife attractant – drawing in beneficial insects for pollination and pest control as a nectary plant.
Covers the soil, growing quickly and outcompeting other plants, preventing grass or weeds from growing into a certain part of your garden when planted along a boundary.
Is an attractive ornamental plant, with pretty flowers over a relatively long period in summer.
Provides yields for people and livestock.
The variety of comfrey most commonly grown in UK gardens in Bocking 14, which is a sterile variety which will not produce seeds. It is most commonly grown either from crowns or from root segments from existing plants. These can be purchased online from a number of different sources and will grow readily and quickly in a variety of different soil types and conditions.
As you will discover towards the end of this guide, however, there are other comfrey varieties that you might consider.
Comfrey is incredibly easy to grow – so much so that it can sometimes become a problem. Some types can spread very easily, which is why the sterile type Bocking 14 is often used. These are perennial plants that will remain in a garden over many years. They are fully hardy and extremely low maintenance, with large leaves and nodding, tubular flowers in purple, pink or white.
Once planted, it will be difficult to eradicate it from the spot in which it was placed. Comfrey has extremely deep tap roots and will regrow from even the smallest section of root. So you must choose your planting location carefully as it will be difficult to change this later.
Sterile varieties of comfrey, of course, cannot be grown from seed. However, common comfrey and some other varieties can be grown from seed as well as from root sections or crowns.
Comfrey seeds sometimes may need a period of cold stratification prior to sowing. When provided with the right conditions, at temperatures between 15 and 25 degrees C., they should germinate within a week or two.
The seedlings can then be pricked out and potted on into containers at least 20cm deep, and promptly planted out into their final growing positions after spending a winter undercover.
Ideally, you should plant out your offsets in March, April or May, though it is possible to begin to grow comfrey later in the season too.
You can take root divisions of an existing comfrey plant. New plants should grow extremely readily even from small 5cm sections of root. You can pot these up, or simply place them elsewhere in your garden where you would like more comfrey to grow. If the sections also have some above ground growth, or a crown portion from division, these will get off to a quicker start.
Take the root sections or divisions and place them (horizontally in the case of root sections) into the soil at a depth of around 5-10cm. Make sure you water them in well, especially if conditions are dry.
Remember when spacing that the plants can grow to a fairly large size when mature. However, if you harvest your comfrey then it is not going to get out of bounds and you can keep it contained as long as you are sure to choose a sterile variety so it does not self-seed prolifically.
Pruning comfrey is not really a separate job but rather, should be considered the same thing as harvesting. Since you will be harvesting, typically 2-3 times throughout the year, additional effort expended to prune the plants will not be necessary.
However, if an area has not been harvested, you can simply cut back after the plant has flowered to encourage a new flush of growth, or keep your garden neat towards the end of the growing season.
When you will 'harvest' comfrey very much depends on how and where exactly you plan to use it. For garden use, comfrey is typically harvested by cutting back or even mowing 2-3 times over the summer season. Comfrey grows quickly and when it is cut back hard, new leaves should quickly emerge from the base until the whole aboveground portion of the plant dies back for winter.
The leaves for medical use are harvested in early summer before the plant flowers, the roots are harvested in the autumn. Both are dried for later use. But remember that caution is required and you should not attempt anything without consulting a herbal medicine professional.
Comfrey is a delightfully low-maintenance and easy plant. You will rarely find that it has any issues and it is tolerant of a huge range of growing conditions and environments.
Rust fungus may occasionally arise, and where it does, sprinkling wood ash around the plants to provide a high potash feed can help.
As mentioned above, some comfrey varieties may be grown from seed, but the most common sterile variety is propagated vegetatively, by means of division of existing plants or by means of root cuttings.
Root cuttings and divisions are typically taken once the plants have entered dormancy and the above ground portion of the plant have begun to die back, in autumn.
Comfrey will as mentioned above die back for winter. But the roots will remain healthy below the ground and the crowns will survive easily here in the UK, bursting back into new growth in the spring. Mulching well with organic matter can help protect the crowns and roots but more importantly, will replenish the soil nutrients around your comfrey plants.
Comfrey leaves have a range of uses and, as mentioned above, provide a range of yields, including:
Chop and drop/ mulch material with a reasonably high potassium content and other nutrients.
Good additions for a composting system.
Material to make a liquid plant feed (see below).
Forage/fodder for chickens, or other livestock.
Roots and leaves for topical herbal medicinal use.
Edible yields and medicine taken internally are also considered by some, though extreme caution is required and generally, internal use/ ingestion is not recommended.
I chop and drop comfrey leaves around fruit trees, and spread them as a mulch around fruits like tomatoes in my vegetable garden. I also layer comfrey leaves in a potato trench when planting, and use them to make a liquid plant feed similar to a commercial tomato feed.
One important way to use the nutrients accumulated by comfrey in your polytunnel is to create a liquid plant feed – sometimes known as 'comfrey tea'.
You can make this comfrey plant feed by submerging comfrey leaves in water and allowing them to break down. Choose a large bucket with a lid, and be careful not to position it too close to your home or to seating areas (it really stinks!).
Once the leaves have rotted down, and the comfrey water mix is a deep brown sludge, you can dilute this mix with water (until it it the shade of a strong cup of tea) to make your plant feed, which is perfect for tomatoes and for other fruiting plants.
There is no need to be hugely precise when it comes to quantities, especially since we cannot measure precise concentrations or nutrient profiles accurately in a home setting.
Another option is to create a comfrey-tea concentrate by compacting comfrey leaves into a collection vessel with a hole at the base through which, as the leaves decompose, the sludge can drip down into a container below. This solution can then be watered down to the same strength as above for use by diluting to around 20:1.
As we have already established, comfrey is not at all challenging to grow and is very easy to care for. But understanding the conditions it likes best can help you achieve the best possible results.
Comfrey can grow well in full sun or partial or dappled shade.
The soil should be consistently moist yet free-draining. Though comfrey can cope with a wide range of soil types and pH levels, it will do best in a loamy soil rich in organic matter, with a slightly acidic to neutral pH.
Comfrey will grow best where consistent soil moisture is available, though this is a plant which does have some drought tolerance once established.
Tolerant of both extreme cold and pretty hot temperatures, comfrey can cope with a lot when it comes to the temperature and can therefore do well in a range of different climate zones. It can easily cope with any of the temperatures we can expect here in the UK.
Comfrey is very good at seeking out nutrients from the soil, including from deeper layers where many other plants' roots cannot reach. Other than providing an organic mulch, replenished each year, other feeding will not be necessary.
Symphytum x uplandicum (Russian comfrey)
'Bocking 14' is, as mentioned above, commonly grown in the UK, because it is a sterile variety that will not set seed and spread in this way. Due to hybrid vigour it provides higher yields than some other varieties. It is high in allantoin and potassium and resistant to comfrey rust.
Another variety, 'Bocking 4' is recommended as poultry feed and is lower in allantoin and higher in protein.
'Harras', a newer cultivar, is alkaloid free.
This native species is commonly found in the UK on riverbanks and in roadside ditches but can also be cultivated in a garden.
Also known as large-flowered comfrey, this is native to the Caucasus region. It has a number of cultivars, and has also been hybridised with Russian comfrey to yield a number of different ornamental varieties of Symphytum × hidcotense.
This is a blue-flowered species native to the Caucasus that is sometimes also used as an ornamental plant.
Comfrey is usually problem-free, though as mentioned above, some types can occasionally suffer from fungal rust.
Remember that comfrey is a large and vigorous plant that will be difficult to move or remove once established. So think carefully before placing it inside a polytunnel. However, it may be beneficial in a corner of the space to draw in pollinators etc., or outside but nearby – perhaps next to a compost heap so that it can gather up nutrients leaching from it.
Drugs.com, (2006.). Comfrey. Available at: https://www.drugs.com/npp/comfrey.html [Accessed 07/03/24]
