Cautious about comfrey -- advise and reassure me!

Everything I am reading about comfrey is that it is beneficial and invasive! The two seem kind of opposing. I understand that True comfrey multiplies but root division but how fast does it divide and if one were to keep cutting back the edges and mowing the areas we want it to stop will it just stay in that area? I only have a 3/4 acre residential lot and I don't want it to take over my neighbors yard and have them angry with me. I have a large area under some pines that nothing grows, 50 years of pine needles the area is just dust and needles. It gets moisture but the moisture leaves right away.

If I use it to restore the area what happens when I want it out of there to plant something else?

or does it spread via seed?

Comfrey patches should be viewed as permanent features - eliminating a patch is very difficult and would be a long term process. You don't want to plant comfrey anywhere the soil will be disturbed - broken root sections will form new plants, and this is actually the main way that we cultivate new plants (by dividing the roots of existing ones and planting root sections in new places.

Ideal comfrey locations include:

around compost heaps - their roots trap nutrients leeching from the heap so they can be recycled

Under fruit trees - they mine nutrients from the soil and as the leaves break down the soil is enriched. A thick clump also suppresses grass which vigorously competes with the tree roots

As a herb layer beneath/beside hedgerows

Out of the way corners where it can be grown for mulch to use elsewhere

Avoid comfrey anywhere you might want to grow annual vegetables - you will never shift it again. I made that mistake with jerusalem artichokes 5 years ago and still have jerusalem artichokes popping up every year.

If you buy named varieties - the bocking #4 or #14 for example - they are sterile and will not set seed, so if you don't disturb the roots they will only spread very slowly.

As Michael has said, Bocking 14 is the way to go, I have root cuttings coming along in a cold greenhouse which will be planted out this year and ready for cropping in 2016. Out in the wild I have found 2 patches of comfrey, one is the 14 strain and the other is an unknown but has self seeded everywhere, its not good news for the landowner but a win win for me as I can harvest as much as I need for making comfrey tea, cheers Dave

Good answer, Michael. I would add

Along permanent fences, to suppress grass from growing through or under the fence.

If your primary reason to have comfrey is to use it as a dynamic accumulator and then chop and drop, make comfrey tea fetilizer, essentially as green manure, then the Bocking clones are appropriate choices. They do not seed and only reproduce through root spreading. Which means not very fast and not very far, but you will have a hard time getting them out of there once established.

If you want to use the medicinal herb aspects of comfrey, then you want the officinale species, not the Bocking clones nor Russian comfrey. Different alkaloids. The officinale does reproduce by seed, so has some potential to spread.

I do not find the term "invasive" to be very helpful. Tends to tell me more about the speaker than about the plant Comfrey is not an aggressive plant, as bittersweet or bindweed that will clamber up other plants and pull them down. It does not spread aggressively like runner bamboo types, that continually try to expand their area. With regular chop and drop harvesting of the intended bed and mowing the lawn alongside, it will be pretty easy to contain. Will it tend to expand into an adjacent bed? Probably. Might want to isolate it, or plan for it to expand to fill in any bed where it is planted.

I would not be afraid of it. Not like it is something toxic that you do not even dare touch

This topic title is awesome. I just imagine a huge mean comfrey plant coming out from behind the fruit trees and sending all the farmers running.

I would be curious as to how many bad situations have actually been had with types of comfrey that spread by seed. I have read from many sources that true comfrey will just reproduce and take over via seed, many of them appear to be primarily interested in bocking varieties. Some of those seem like simple repetitions of someone else's past experience, but maybe in certain climates it is worse than others.
As soon as I hear a beneficial plant is a horrid invasive nightmare I buy some seeds and plant it, so I have comfrey officinalis growing comfortably in my yard.
No horrible problems yet, and I can't imagine it could be worse than the other strong invasives that are in my yard. Then again my whole neighborhood holler is a who's who of invasive exotics and strong native growers, that is to say my neighbors wouldn't even notice if a plant I planted spread to their property.