Comfrey easily takes hold via root cuttings and crowns. But how about just a leaf?
There's a single thread on Permies from many years ago, one n00b (at the time) wrote 'I place comfrey leaves in water, and they grow roots and I plant them and they become new comfrey plants.' Another n00b (at the time) said 'Yeah me too'. Followed by a smattering of others saying 'Hey! I didn't know you could do that, I need to try that!' Then the thread dies, and the two n00bs aren't heard from again on Permies.
I tried it. Found four healthy leaves (difficult to do in January!), dropped the stems in water with a drop or two of rooting compound, and placed them in a 65 degree basement under grow lights.
Over a month later, three leaves are shriveled, gone. One is still reasonably healthy all things considered, still a nice green color. No roots have appeared.
My question: Has anyone here successfully propagated comfrey from just *leaves*?
I've always been mad, I know I've been mad, like the most of us have. Very hard to explain why you're mad ... even if you're not mad.
This only happens if you don't want it to I expect. I've certainly had comfrey leaves trying to root where I didn't want them, so they never got a chance to survive. I think it was when I mulched round my tomatoes in the polytunnel with fresh leaves, so that would have been warmer and dirtier than your set up. You may have better luck trying later in the year with bigger leaves perhaps.
I haven't ever tried propagating comfrey from just leaves but I might guess the more of the base of the leaf you have, the better the result... or perhaps waiting until it has a few leaves and taking the very top of the plant (like the beginnings of a crown offset) would be more successful?
If I can find the space I might try a few and see what happens.
I haven’t tested this but I believe I read that the thicker flowering stems will root. The comment suggested not using the stems to mulch around plants in case they rooted in a spot where you didn’t want them.
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With the larger leaves, I think you'll need to trim the leaf part way back, leaving maybe a 1 inch square surface. This is recommended for other plants. Doing this helps the cutting put energy into make roots, instead of trying to support a large leaf surface.