Who would have thought the word ‘duff’ could have so many different meanings? I’ve just searched it on the internet and the international variations are quite… extreme. In my mind, ‘up the duff’ was going to be a slightly suggestive heading connecting urban soil to pregnancy; slightly suggestive, in subtle as a brick kind of way. But the internet would suggest that my heading is more slightly suggestive in very odd, bordering on a somewhat disturbed kind of way.

Duff, in this context, is not about being pregnant or any of the other 33 more peculiar definitions, but about leaf-litter and all of the good things that live in it. If you were to envisage a soil profile as described in a text or course book, duff would be the ‘O’ horizon; the uppermost layer of a soil profile, the one with the highest percentage of organic matter (dead leaves, twigs and other plant matter in various stages of decomposition). Duff is all of that, plus the microbial soup that exists in that layer.

I first was introduced to duff as a description of organic matter while in America. I had just finished a presentation citing all the wrongs arborists do under the name of tree care, and a man asked me if I would recommend introducing duff into a planting hole. The context around this was ‘eco-sourcing’ (selecting and growing plants from the local region, for the local region). I had pointed out that there wasn’t much in a built environment that resembled the original environment, therefore, the assumption that if a tree once grew there it will now grow there, isn’t as logical as it first seems. I had discussed the pros and cons of ‘compost tea’ and ‘sugar supplements’ as methods of improving soil health [NB; the scientific jury is still out on those, it seems that there is a short-term boost but there is minimal long-term benefit], his question was around the reintroduction of local soil organisms into urban soils. It was a good question.

The issue with compost tea and sugar, is that there is no substance to it. Think of them a bit like energy drinks, a quick peak of metabolic activity followed by sugar crash. When your energy levels drop, if you are so inclined you can have another energy drink… Doctors and health officials tend not to recommend energy drinks as part of a balanced diet, I think the same can be said for about compost tea and sugar; it shouldn’t be considered as a long-term solution to improving soil health.

But what about duff? We are told that a teaspoon of top-soil can hold up to one billion bacteria, many meters of fungal hyphae, thousands of protozoa, and herds of nematodes. There can be no denying that duff has substance. So what would happen if we added a single teaspoon of duff to a planting hole?

I suspect when I answered him, based on three seconds of consideration, I came up with an answer based on the very real possibility of spreading a-hundred-and-one pests and diseases per teaspoon of duff – so I most likely embraced the Kiwi default phrase; ‘Yeah-nah’ (meaning no).

But, assuming for a moment that all of this substance is good substance (or at least not bad substance), and there is no issues with ‘pinching soil’ from a National Park and/or transporting biological organisms from one place to the other… would taking a teaspoon of duff from a natural/un-disturbed environment and adding that duff into planting hole be a good thing?

Yes, I believe introducing duff to a planting hole probably won’t hurt and could even be beneficial. As Nietzsche said: “That which does not kill us makes us stronger’. But for there to be a benefit the duff would have to contain only good (or at least not bad) microbes, it would have to be fresh and there would have to be some life and organic matter in the soil (the rest of the soil in the planting hole).

I don’t see duff as the silver bullet – you can’t just add duff to bed-rock or clay and hope good soil appears. Duff won’t solve drainage or break a drought and a teaspoon of good substance won’t necessarily fix a cubic meter of bad substance. If you are planting exotics then a teaspoon of native duff may do little to help those particular plants.

But to answer his question; should we ‘up the duff?’ Plants need healthy soils and healthy soils are mix of aggregates, organic matter, water, air, and living soil organisms. I’m not opposed to the idea of adding duff to a soil assuming it’s the right duff.