It's high time for an update on our no dig potato and cabbage patch, first documented back in my May 12th, 2021 entry.
In the first year, 2021, neither of us were especially impressed with the performance of this bed. The non-porous structure of the cardboard did exactly what I had feared it would do, creating a hydrophobic environment in which water ran off the surface, causing the soil beneath to dry out at a faster than average rate.
The roots of the potatoes, planted parallel to or just above the surface of the cardboard — as recommended in several sheet mulching guides — failed to penetrate deeply into the soil.
As a result, the crop didn't perform as well as we had hoped. The yield was a little underwhelming even after taking into account the blight induced early harvest.
By the second year, 2022, the cardboard had still not completely decomposed. We filled the bed with a thick layer of manure from a local horse owner, then added our usual cover mulch of straw and hay. Later we planted onions and cabbage varieties here.
As in the first year, the remaining cardboard constricted valuable water flow through the soil. This exacerbated the difficulties caused by the hot, dry summer we experienced that season.
Our cabbage crops especially struggled in this bed. When we dug up the most underperforming plants and moved them to a part of the bed where the cardboard had completely decomposed, the plants responded quickly to the uncovered soil and began to develop more healthily.
In both years, weeds appear to have been suppressed, but we can see that there are plenty of roots tangled and thriving and ready to grow back. This is of course not to be considered a report of a serious study. We did not proceed with any sort of control group, nor did we document the myriad variable conditions with an eye to repeating the experiment.
To reiterate from my original post, this bed was very quick and very easy to construct, and it did produce a crop in both years. If you're short on time or have health problems that prevent you from digging and performing heavier work, this could be a great option for growing food with minimal manual labour. As it uses waste material that you may already have on hand, it can be considered a form of recycling. It may also require less initial input than other no dig methods that use thick layers of woodchip and coarse organic matter. Although I would always advocate for these where they are an option.
I maintain that the biggest disadvantage of sheet mulching is its well documented potential to restrict aeration of the Earth below, which has effects that are difficult to measure from a general garden level observation. It's also worth noting that — in contrast to our drought problems — the sheet mulching barrier has been shown to prevent adequate evaporation and drainage on wet or poor draining soils.
These are interesting points considering that the method is part of a philosophy which attests to not unnecessarily disturbing the soil microbiome. Apparently adding a synthetic barrier that deprives the Earth of oxygen, inhibits natural drainage, and interferes with root growth, does not count as a meaningful disturbance.
There are changes we could have made to help water, oxygen and root penetration, and I have encountered some of these in the intervening years, but this highlights one of my recurring problems with the popular permaculture market. Even the simplest practices can be poorly defined, with a range of conflicting opinions and personal anecdotes offered between sources.
I cannot over stress how important I believe it is to maintain a critical, science backed approach to your farms and gardens. At the very least this will help you to avoid sinking time and resources into ineffective methods, and may steer you clear of unintentionally harmful practices.
That said, we may well repeat this process in a few other small areas this year, as we have a lot of spare cardboard lying around in the barn, and it may aid us in quickly expanding the kitchen garden. I just won't be expecting any particularly notable results from it.
