Comfrey: Boon and Bane
When my husband Dale and I first checked out our new vegetable plot in the New Paltz Gardens for Nutrition, we saw masses of comfrey and thought, oh no. It spreads by underground stems in an aggressively jaunty fashion; it’s one of those that if you leave a little piece of root behind, you’ll have a new plant, so it’s very difficult to be rid of altogether. We thought someone had planted it for its herbal uses (external, for poultices that are said to help with wounds and inflammation) and now we had this monster on our hands, which we did not plan to use for cuts and bruises.
While we were digging out our dreaded squatter, a woman came walking round the community garden to a common area and started harvesting big bags of the stuff. We asked her what she uses it for. She told us it makes an excellent mulch for her vegetable garden, that it’s high in Nitrogen, Phosporus, and Potassium (having an N-P-K analysis on par with farmyard manure), that the leaves–low in fiber–readily break down, verily dissolving in two days, and that it can kickstart compost piles with its high Nitrogen content. Well.
We kept most of the patch and started cutting the stems and using them as a topdress alongside our crops. We felt very smug having our own living mulch right in the garden that we didn’t have to haul. We did have fantastic yield last summer, and we could have been tempted to give credit to comfrey, but it was not exactly a controlled experiment, and last summer was just good growing, period. This summer our garden doesn’t look as robust, despite the continued use of comfrey leaves as nutrient-rich mulch.
My real moment of disillusionment has come from realizing that nothing else in the vicinity of the comfrey plants–within at least six feet–grows. I tried squash, cucumbers, onions–even nasturtiums just bit the dust. I did a little web search and see that there are several studies that found that comfrey roots have allelopathic properties. Allelopathy is the clever means by which plants exude toxic chemicals that fend off other plants. There don’t appear to be enough studies to conclude that this is for certain what’s happening, but at the very least, the girthy roots of comfrey are widespreading and are outcompeting my poor little seedlings for nitrogen. Perhaps the soil in this part of the garden is chronically nitrogen depleted because of the comfrey stand’s hegemony.
So now I am thinking that it’s great to have comfrey nearby, but not in my garden plot. I’ll bet that’s why the herb lady comes down to the floodplain to harvest it, rather than growing it herself. Who can blame her?