Is Comfrey Invasive? The Truth About Comfrey Spread

One of the most common concerns about growing comfrey is its potential to become invasive. The answer isn't a simple yes or no—it depends on the variety you choose and how you manage it. This guide will help you understand comfrey's growth habits and how to enjoy its benefits without letting it take over your garden.

The Short Answer: It Depends on the Variety

Comfrey Type	Spreads by Seed?	Spreads by Root?	Invasive Potential
Common Comfrey (Symphytum officinale)	Yes - Prolifically	Yes - Aggressively	High
Russian Comfrey (Symphytum × uplandicum)	Yes - Moderately	Yes - Aggressively	Medium-High
Bocking 14 Comfrey (Cultivar of S. × uplandicum)	No - Sterile	Yes - From fragments	Low-Medium
Dwarf Comfrey (Symphytum ibericum)	Limited	Yes - Moderately	Low

Understanding How Comfrey Spreads

Seed Dispersal

Common comfrey and some Russian comfrey varieties produce viable seeds that can spread throughout your garden and beyond. A single plant can produce hundreds of seeds per season, which can remain viable in soil for several years.

Important: Bocking 14 comfrey is a sterile hybrid that does not produce viable seeds. This is a major advantage for gardeners concerned about invasiveness.

Root Propagation

All comfrey varieties can spread via their roots, though some are more aggressive than others. Comfrey has a remarkable ability to regenerate from root fragments—even a piece as small as 1/2 inch can grow into a new plant.

This regenerative ability is what gives comfrey its reputation for being difficult to remove once established. When roots are cut or broken during cultivation, each fragment can potentially become a new plant.

Is Bocking 14 Comfrey Invasive?

Bocking 14 comfrey, our recommended variety, has a significantly lower invasive potential than common comfrey for several important reasons:

Sterile Seeds

Bocking 14 is a sterile hybrid that does not produce viable seeds. This eliminates the primary way that many plants become invasive—by self-seeding throughout the garden and beyond.

Controlled Spread

While Bocking 14 can spread through root fragments, it does so at a much slower rate than common comfrey and only when the roots are disturbed. With proper management, this spread is easily controlled.

Clump-Forming Habit

Bocking 14 tends to grow in a more contained clump rather than aggressively sending out runners like some other varieties. This makes it more suitable for managed garden settings.

For these reasons, Bocking 14 is considered "potentially spreading" rather than truly invasive. With basic precautions, it can be a valuable garden plant that stays where you put it.

Controlling Comfrey in Your Garden

Strategic Placement

The simplest way to prevent unwanted spread is to plant comfrey in locations where:

You won't need to disturb the soil frequently
Any spread would be contained by structures or pathways
You wouldn't mind if it expanded somewhat over time

Good locations include orchard understories, the outer edges of garden beds, or dedicated perennial patches.

Physical Barriers

To contain comfrey's root spread, consider these barrier methods:

Sunken barriers: Bury barriers like metal flashing, pond liner, or root barrier fabric at least 18 inches deep around the planting area.
Raised beds with barriers: Line the bottom and sides of raised beds with landscape fabric or other barriers before planting comfrey.
Container growing: Growing comfrey in large containers completely eliminates the risk of unwanted spread. See our Growing Comfrey in Pots guide.

Maintenance Practices

These practices help prevent accidental spread:

Avoid tilling: Don't use rototillers or other cultivation equipment near comfrey plants, as they can break up and spread root fragments.
Careful hand digging: When working near comfrey, use hand tools and be meticulous about removing all root fragments.
Mow perimeters: Maintain a regularly mowed strip around comfrey plantings to catch any potential spread early.
Harvest regularly: Frequent cutting prevents plants from flowering (though this is less critical with sterile Bocking 14).

Removing Unwanted Comfrey

If you need to remove comfrey or control its spread, here are effective methods:

Method 1: Persistent Cutting

Cut the plant to the ground.
Cover the area with cardboard or black plastic.
Each time new growth appears (typically through or around the edges of the covering), cut it immediately.
Continue this process for at least one full growing season to exhaust the root reserves.

Method 2: Root Excavation

Water the area thoroughly to soften the soil.
Dig carefully around the plant, working outward from the center.
Remove as much of the taproot as possible (it can extend 3+ feet deep).
Sift through the soil to remove any root fragments.
Monitor the area and remove any new growth immediately.

Method 3: Sheet Mulching

Cut the plant to the ground.
Cover with cardboard or several layers of newspaper.
Add 4-6 inches of mulch on top.
Leave in place for at least one full year.
Monitor edges for any escaping growth.

Important Note

Chemical herbicides are generally ineffective against comfrey due to its waxy leaves and extensive root system. They're also unnecessary given the effectiveness of the organic methods described above.

Is Comfrey Listed as Invasive?

The invasive status of comfrey varies by region:

United States: Common comfrey (Symphytum officinale) is listed as invasive or potentially invasive in some northeastern states, but Bocking 14 is not typically included in these listings due to its sterile nature.
Canada: Not generally listed as invasive at the federal level, though some provinces may have regional restrictions.
Europe: Considered native in much of Europe and not typically listed as invasive.
Australia/New Zealand: Common comfrey is considered potentially invasive in some regions, while Bocking varieties are generally accepted.

Always check with your local extension office or department of agriculture for the most up-to-date information on invasive plant listings in your specific area.

Frequently Asked Questions

Will comfrey take over my garden like mint does?

Unlike mint, which spreads aggressively via underground runners (rhizomes), Bocking 14 comfrey grows in a more contained clump. It only spreads when roots are broken and dispersed, not through running rhizomes. With proper placement and management, it's much easier to control than mint.

Can I plant comfrey near my property line?

It's best to keep comfrey at least 3-4 feet from property lines unless you have barriers in place or your neighbor is aware and approves. While Bocking 14 won't spread by seed, root fragments could potentially cross boundaries if the soil is disturbed.

How can I be sure I'm getting true Bocking 14 comfrey?

Purchase from reputable suppliers who specifically identify their comfrey as Bocking 14. True Bocking 14 has purplish-blue flowers and doesn't produce viable seeds. If you collect seeds from a plant labeled as Bocking 14 and they grow, it's not genuine Bocking 14.

The Bottom Line: Responsible Comfrey Growing

With the right variety (Bocking 14) and proper management practices, comfrey can be a valuable addition to your garden without becoming invasive. Its benefits for soil health, pollinators, and organic gardening far outweigh the manageable risk of spreading when appropriate precautions are taken.

Remember that all powerful plants require respect and management. By understanding how comfrey grows and spreads, you can harness its benefits while keeping it exactly where you want it in your garden.

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