Growing comfrey is like having a double-edged sword in your garden.
It can be an ornamental plant, a gardening companion to prevent pests and fertilize the soil and even as a herbal medicine. But through time, they and end up harming and killing other plants in your garden.
Learn how to control and remove comfrey and use it more sustainably in your garden. Let’s get started on this gardening journey!
What is the common comfrey plant?
Is comfrey invasive?
Comfrey is a perennial plant native to Europe and Western Asia. It is easily identifiable by its purple or pink bell-shaped flower clusters, which pollinators love during summer.
| Scientific Name | Symphytum officinale |
| Common Names | • Black wort • Boneset • Bruise wort • Comfrey • Common Comfrey • Consound • Cultivated Comfrey • Knitbone • Quaker Comfrey • Slippery-Root • True Comfrey |
| Family | Boraginaceae |
| Life Cycle | Perennial |
| Propagation | • Root Cutting • Seed • Crown Division |
| Origin | • Europe • Western Asia |
| Height | 1 to 3 feet |
| Growth Rate | Rapid |
| Maintenance | Medium |
| Light | Full Sun |
| Soil | Clay Loam |
| Recommended Space to Plant | 12 inches to 3 feet |
| Flowers | • Pink • Purple • White |
| Landscape Location | • Container • Meadow • Pond • Woodland • Border |
| Resistance | • Deer • Drought |
| Toxic | Toxic – can lead to liver or lung damage, and cancer |
| Poisonous Parts | • Bark • Flowers • Fruits • Leaves • Roots • Sap • Seeds • Stems |
Comfrey thrives under full sun and less aggressively under partial shade. This plant grows about 3 to 4 feet tall and 2 to 4 feet wide.
It thrives in clay or loam soils and needs consistent watering, although it can survive droughts.
Comfrey reproduces rapidly through its roots, seeds or via crown division, making it notoriously difficult to remove in gardens. They also have large taproots, which enables them to bioaccumulate nutrients in the soil and deprive other native plants.
Is comfrey invasive?
Comfrey is a highly invasive plant with every fragment of its roots capable of turning into a new plant. Once it spreads, it bioaccumulates nutrients from the soil, depriving other plants or crops in the garden.
When left unchecked, it can take over your whole property and destroy the balance in your garden’s ecosystem. It will compete with plants with the nutrients in the soil and eventually kill them.
Why do gardeners grow comfrey?
Gardeners grow comfrey plants to use them as an ornament, to control pests and diseases, as a natural fertilizer, and to harvest herbal medicine.
Let’s first understand each benefit of the comfrey plant.
1. Comfrey is an ornamental plant.
Comfrey is a popular groundcover perennial plant because it can improve the soil’s condition over time. It also produces purple and pink bell-shaped flower clusters that bees and butterflies love.
2. Comfrey is used to control pests and plant diseases.
Despite their invasive character, the comfrey plant can help control pests and diseases in your garden. It keeps slugs away from the plants or prevents them from getting powdery mildew.
3. Comfrey is a natural fertilizer.
Comfrey is an excellent source of food and fertilizer for plants. Because of its high nutrient content, comfrey can be used as a mulch, liquid fertilizer, animal feed, or nitrogen-rich compost material.
4. Comfrey can be an herbal medicine.
Comfrey is also popularly known as “knit bone,” a traditional first aid medicine to treat external injuries like fractured bones, torn joints, burns, bruises and muscle sprains.
How to Control Comfrey
There are four practical ways to control comfrey growth in your garden: keep it in one spot, use a sterile comfrey seed, place it in shaded areas and trim it regularly. Read on to learn how to control comfrey plants or their garden invasion.
1. Keep comfrey in one spot.
Comfrey plants must be contained to limit their spread in your garden. You can keep them in one permanent spot, like in tall raised garden beds, tall containers, wrap-around trees, and enclosed containers.
Here’s how you can keep growing your comfrey plants in these places.
Raised Garden Beds
Grow your comfrey plants in raised garden beds, preferably stainless steel mesh. You can add drainage barriers and ample space to check the comfrey roots below.
Make sure that there are no other plants or vegetable seedlings near the raised garden beds that you dedicate for comfrey plants so that no leftover roots will grow back and take over the new plants.
Tall Containers
Comfrey roots tend to grow deep and form vast root systems. This is why tall containers and deep planters are ideal places to plant comfrey plants.
If you plan to grow and control your comfrey plant this way, make sure that the tall container has drainage holes and is placed on top of hard surfaces like cement, tiles or bricks so that it won’t grow new plants.
Around Trees
The comfrey plant is a popular ground cover for trees, and the good news is you can use this behavior to limit its spread. All you have to do is to plant comfrey about 12 to 15 inches from the base and trim them regularly.
You can even gather those stem cuttings, allow them to wilt and use them as fertilizer for the tree. This way, the comfrey plant will keep the tree and its soil healthy.
Enclosed Corners
You can dedicate one enclosed space in your garden where the comfrey plant can spread freely on the ground.
Just make sure they’re far from other crops and vegetables. Place mulch or a black plastic sheet to keep them in your chosen spot so they won’t grow past them.
In the long run, the comfrey plant will be an ornamental shrub in your garden where pollinators can enjoy its purple and pink flower clusters.
2. Use a sterile comfrey variety.
Sterile comfrey varieties do not produce fertile seeds, which minimizes their spread in your garden. They usually grow tall, but no matter how many insects, birds or the wind spread the seeds, they won’t germinate.
For instance, you can use the Bocking 14 and Bocking 4 sterile comfrey varieties. They are Russian cultivars that can be propagated through roots and crown divisions but not through seeds, limiting their spread.
We also recommend planting the Russian comfrey, known as “the star of the permaculture show.” This variety produces few seeds, which only grow when planted.
3. Place comfrey in shaded areas.
Comfrey plants love the sun, fertile soil and consistent watering, so the trick is to hold back on these three things they love.
You should place your comfrey plant in a partially shaded area, such as under trees, so they won’t get much sun or moisture that makes them grow vigorously.
4. Trim comfrey regularly.
Comfrey plants usually bloom in late May or early June, when they start spreading vigorously. That’s why it’s best to cut back on mature comfrey plants before they bloom in these months or before the flowers start seeding.
You can trim your comfrey plants when they grow 5 to 6 inches from the ground. Do this regularly, preferably 3 to 4 times every year.
How to Remove Comfrey
Sometimes, keeping an invasive comfrey plant is not worth the trouble, especially when killing other plants in your garden. Read on as we walk you through the different ways to remove comfrey plants.
1. Dig out the comfrey plant.
| Difficulty | Easy ●○○○○ |
| Duration | 30 minutes to 1 hour |
| Things You Need | • Trowel • Strainer • Black plastic sheet |
Digging out comfrey works best for young plants or seedlings. As you apply this method, make sure not to break any roots because this will only encourage them to grow new plants.
Additionally, a black plastic sheet on top of the planting area will prevent sprouts from reaching maturity because of a lack of sunlight.
Below are the steps on how to properly dig out comfrey plants.
| How To Do 1. Loosen the soil around the comfrey plant. Do not break any roots. 2. Gather every root that you can find. 3. Use a strainer to filter through the soil. 4. Cover the area with a black plastic sheet to prevent plants from growing or seedlings from sprouting. |
2. Mow and mulch the comfrey plant.
| Difficulty | Easy ●●○○○ |
| Duration | 30 minutes to 1 hour |
| Things You Need | • Lawnmower • Mulch or wood chips • Rake |
As comfrey plants mature, they become harder to remove because of their large taproots and flowers with tiny seeds that allow them to spread rapidly.
This is why mowing and mulching comfreys are a more effective method to remove mature comfrey plants. Here’s how.
| How To Do 1. Mow the comfrey plants to ground level. 2. Gather and remove all cuttings and flower stalks in the area. 3. Cover the area with mulch, such as wood chips, to prevent further comfrey invasion. 4. Once the comfrey plant dies off, rake the wood chips from the area. |
3. Apply an organic solution.
| Difficulty | Easy ●●○○○ |
| Duration | 30 minutes to 1 hour |
| Things You Need | • Vinegar • Lemon or citrus fruit • Water • Sprayer |
Applying an organic solution to the comfrey plant will keep other crops and plants safe while getting the job done. The solution will only burn the comfrey’s cell membranes until it wilts away.
Here’s how to apply an organic solution to remove your comfrey plant.
| How To Do 1. Prepare 1 quart of vinegar and 4 ounces of citric acid from lemon or any citrus fruit. 2. Mix the vinegar and citric acid with water for a 5 to 30% concentration. 3. Transfer the solution to the sprayer and apply it over the comfrey plant. 4. Repeat the application until the comfrey plant dies off. |
4. Use a chemical herbicide.
| Difficulty | Easy ●●○○○ |
| Duration | 30 minutes to 1 hour |
| Things You Need | • Non-porous plastic • Chemical herbicide • Water • Sprayer |
There’s one sure way to kill off comfrey, and that’s by using chemical herbicides containing glyphosate.
Glyphosate inhibits an EPSP synthase enzyme, which makes the proteins that plants need to grow. Without it, the plant will die.
However, glyphosate is a powerful chemical that can kill most plants effectively, so you should prevent them from spreading to surrounding plants.
Below are steps to safely apply glyphosate to remove the comfrey plant.
| How To Do 1. Cover the surrounding plants with a non-porous plastic. 2. Fill the sprayer with the chemical herbicide and water. 3. Spray the chemical solution on the comfrey plant thoroughly. 4. Wait at least a week to see if the comfrey plant has died. If not, spray more chemical herbicides. |
5. Uproot the plant using a weed removal tool.
| Difficulty | Average ●●●○○ |
| Duration | 1 to 2 hours |
| Things You Need | • Pruning shears • Weed removal tool |
The comfrey plant’s extensive taproot system can grow as deep as two meters, making it absorb many nutrients even in the subsoil.
You’ll have to uproot the plant using a weed removal tool to work around its deep root system. Here’s how.
| How To Do 1. Cut the top of the plant, leaving 6 inches of the stem above the ground. 2. Using a weed removal tool, grasp the stem and pull the roots up. 3. Thoroughly comb through the soil as you pull out the plant to make sure no root is left behind. |
Sustainable Uses of Comfrey
Once you’ve successfully removed the comfrey plant from your garden, don’t throw it right away because you can still use it to enrich other plants, your soil or make a tea out of it.
1. Chop-and-Drop Mulch
Comfrey is a dynamic accumulator because its extensive taproot system can reach below the root zone of most plants and use all the nutrients below to keep itself healthy.
This means that most parts of the comfrey plant are rich in nitrogen, phosphorus and potassium – the macronutrients essential to every plant’s survival.
So, to create a chop–and-drop mulch out of this plant, prune back the plant during the growing season, and apply two to three layers of leaves around the plants.
This way, the comfrey mulch will prevent weeds from growing while releasing its macronutrients into the soil.
2. Compost Activator
Another way to take advantage of the comfrey plant’s high nitrogen content is to use it as a compost activator. All you have to do is to plant comfrey near your compost bin and add it there regularly.
Just make sure to keep the proper nitrogen and carbon balance in your compost. Less nitrogen content from comfrey may slow your compost down.
3. Liquid Fertilizer
| Difficulty | Average ●●●○○ |
| Duration | 1 to 2 hours for preparation 6 weeks overall |
| Things You Need | • Comfrey leaves • Large sealed container • Rock or bricks • Water • Sprayer |
Those uprooted comfrey plants still contain many nutrients from the subsoil, and the good news is you can turn it into a liquid fertilizer. The nutrients from the liquid fertilizer will encourage plants to grow and produce flowers.
Follow the steps below to make your liquid fertilizer.
| How To Do 1. Gather comfrey leaves and place them in a large container. 2. Crush the leaves using a rock or brick. 3. Cover the container for six weeks to allow the leaves to break into a thick black liquid. 4. Dilute the liquid in a ratio of 1-part black liquid to 10-part water. 5. Spray the liquid fertilizer to side-dress your plants. |
FAQs on Comfrey Weed
Some non-invasive alternatives you can plant instead of comfrey are anise-scented sage, lungwort, Lamb’s ear, common harebell, and Berggarten sage.
Comfrey is a weed since it is a leafy perennial plant that spreads quickly through its seeds, root cuttings or crown division and competes with surrounding plants’ nutrients.
Humans should not eat any part of the comfrey plant because they contain a toxic chemical called pyrrolizidine alkaloids, which can cause liver or lung damage and even cancer.
Comfrey is a herbal drug or medicine used to treat external wounds, sprains, broken bones and inflammation. However, comfrey is unsafe when taken by mouth because of the poisonous pyrrolizidine alkaloids it contains.
