Bruce at RED Gardens has found double-dug gardens to be more productive:
I have used this method of garden creation for some years now ever since reading John Jeavons’s book How to Grow More Vegetables.
There are concerns with it, of course.
- Disrupts soil layers
- Destroys microbial and fungal life
- Is labor intensive
- Is not something you see in nature
Yet I cannot argue with the results. Our double-dug beds have always done well. Always. There has never been a time where I put in the effort to double-dig and then said “man, that wasn’t worth it!”
It may be, as Bruce notes, that double-digging initially to clear rocks and remove soil compaction followed by using a no-till or other method may be a better practice than breaking the soil again year after year.
More experiments – as always – are in order.
Yes, I would lean to the “do it once” conclusion. That said it’s so much work, and I’ll no longer do it. That’s for my younger self. 🙂
You make one good point here: none of us should be slavishly following a particular cultivation practice. Even though I have been bio-intensive gardening for 40 years, and prefer this method (even in my “old age!”), I do think we should constantly evaluate the health of our soil and make cultivation decisions that minimize disruption while supporting a healthy, deep, nutrient profile. I’d like to point out, however, that all four of your criticisms of double digging perpetuate common misunderstandings of the basic premises of the bio-intensive method as taught by Alan Chadwick and John Jeavons.
1. Proper double digging actually preserves (and enhances) soil layers, always keeping the top three inches (where much of the active microbial life resides in a healthy garden bed) intact and on the surface, and forming new layers of organic matter deep in the soil profile.
2. Rather than destroying microbial life, double digging deepens the aerated portion of the soil profile, multiplying the cubic area that is available for microorganisms to proliferate in.
3. Although, the initial preparation may seem labor intensive, over the long haul, bio-intensive beds require extremely low labor inputs. If you’ve ever had the privilege of double digging an established bed, you’ve experienced the truth of the claims that these beds require minutes, as opposed to hours, to prepare. Usually, the job can be done without breaking a sweat in less than a half hour per 100 ft2. Further, once established, bio-intensive beds are generally not double dug every year, but can be simply broadforked and amended before each new crop.
4. Finally, the whole premise of double digging was based on the observation that in nature, the action of landslides creates a bio-active environment in which plants flourish. Correct double digging is like creating tiny landslides that both aerate and tip the soil layers at an angle, encouraging life to permeate deeper into the soil profile.
Hope that helps to answer some of the common criticisms of the method.
Carla, I’m afraid it is you that is perpetuating common misunderstandings. Jeavons is not a soil biologist, he has no training, education or expertise on the subject at all. He has never even bothered to do a basic scientific trial comparing any aspect of his scheme to anything else.
1a. Digging can not preserve soil structure. Keeping the soil that was in the top inch on the top does not matter. Soil contains a vast living network of fungal hyphae, you can not dig without destroying it.
1b. The myth that most microbial life is in the top 3 inches (or 4, or 6) comes from people killing their soil, working compost into the top, and then saying “look there’s only microbes in the top few inches”. There should be a healthy rhizosphere creating soil for as deep as you have dirt.
1c. Double digging actively hinders the formation of organic matter deep in the soil profile. It creates a layer of dramatically different density, which disrupts the capillary flow of water. This causes roots to avoid further downward growth, so you limit the depth of roots. And stable organic matter is creating almost exclusively from the root exudates of living plants, so you limit the depth of your top soil.
2. Roots and arthropods will do all the aeration needed, just as they do in nature. Double digging adds excessive air, which creates conditions where organic compounds are fully decomposed into CO2 and H2O. This is the opposite of building soil organic matter.
3. Not digging is much less effort than digging twice. It also lowers weeds, so you have less effort spent dealing with that problem. And it provides greater yields, builds soil, and requires no fertilizer of any sort. Digging is a bunch of work that lowers your long term fertility, makes you dependent on fertilizer or a crazy compost growing scheme, encourages rampant weed growth, and produces lower yields.
4. That’s a very poor observation. In nature, landslides create areas of bare dirt and disrupt and destroy all fungal life. As a result, early succession colonizing plant species that thrive in low fungal dirt sprout and take over, thriving in their ecological niche. We tend to call these species “weeds”. All soil destroying techniques like plowing, tilling, digging, etc. all share this same common issue: they are creating the ideal environment to grow weeds. Almost all vegetables people grow are mid succession plants that grow best in a balanced bacterial and fungal soil. By destroying the fungal life, you make it harder for your crops to grow and easier for weeds to grow.
Search for Elaine Ingham on youtube if you want the scientific details, or search Gabe Brown if you want the “just tell me how to do this” version from a farmer.
Bob, I feel like the no-dig movement (and generally the current “environmental” movement too) romanticizes nature, without looking at actual biology. Living in Canada, where for the most part, soil development has only resulted in approximately 15-25 cm of topsoil since the retreat of glaciers, it is clear that natural processes of soil development can be extremely slow (at least when applied to a human timescale). As an archaeologist, I’ve dug from coast to coast in Canada and in numerous different soil types, and I can earnestly say, that the deepest soil development I’ve ever seen has been in areas farmed in a traditional fashion during the last two centuries with plowing/digging. From indigenous practices of burning forests to increase overall biomass, to coppicing and pollarding, humans have always found ways to maximize productivity from the environment. If digging has worked for millennia, why is it suddenly seen as evil and unnecessary? The earth will always be more productive with active human intervention. Look up terra preta.