Double Digging, Intensive Gardening, French Bio-intensive, whatever current buzzword is trotted out to sell the latest gardening book. The most sacred of sacred cows. And a complete waste of your time and effort. Compost Myth-busting returns!
Digging and especially Double Digging (turning the soil completely over) is a backbreaking waste of time. Digging destroys the delicate soil structure which exists even in badly abused soil such as that found in:
- Weedy vacant lots
- High traffic areas worn down to bare earth by human or animal traffic
- Recently de-paved areas
- Average round-up drenched american lawn
- Narrow strips between a side walk and street or retaining wall or other gaps between paved areas.
What do I mean by soil structure? The delicate web of beneficial earthworms, fungi, insects and microbes existing beneath your feet no matter how abused the soil. Digging, tilling, cultivation and plowing all destroy this delicate natural web the way a tornado rips through a trailer park. Preserving this delicate structure and integrating with your new bed should be your number one goal.
Your soil structure goals should be from top down:
- Top layer of mulch to protect the bare surface (straw or wood chips in my suggested method)
- Decaying humus layer (finished compost in my suggested method)
- Soil which is completely undisturbed
- Subsoil (mineral rich but nuturient poor)
In nature these four layers exist automatically without digging and are what your plants expect. The top layer is undecomposed leaves or dead grass, the next humus in the form of partly decomposed leaves or grasses , then the soil, and finally the subsoil. Plants want these in the same order they exist naturally; burying compost or other organic material by digging disrupts nature.
Straw or wool chip mulch used as a covering blanket serves to protect the soil from erosion and helps suppress windblown weed seeds. The mulch emulates the fresh layer of undecomposed material on the surface. Compost belongs on top of the soil where it emulates the natural humus missing in abused areas. The two covering layers together hold water and stimulate the beneficial activity of the life process in natural soil structure below. They emulate what is missing in abused soil without disrupting the beneficial processes already present.
The misguided theory for digging in organic material or compost, is to distribute it where the plants roots will be. However, the shallow surface roots of plants are designed to extract water and nutrients from the soil surface structure where the most recently decomposed humus would be in nature as discussed above. Deep roots on plants serve to bring up minerals from the subsoil and hold the plant down in extreme conditions.
Please note that planters, self watering pots, and ultra raised beds (more than six inches) are not what I am discussing here. I have seen all of these work very well, but you will need to work to establish the soil structure in these pocket environments and you will need a lot of inputs to get the balance right. See future posts for discussion on some of these options which are appropriate in limited spaces such as a balcony, a rooftops, indoors, or if you have a microscopically sized backyard typical of the urban enviroment.
I can see the comments already: But my conditions are special, I have crabgrass, bindweed, clay, sandy, dry, wet, toxic, fill in the blank soil. I need to waste time and money and ruin my back. Everyone here in my city, town, desert island says so!
Everyone says so because everyone read the same damn articles in The Mother Earth News over the years and thought “If it is backbreaking it must be good, right?”.
Wrong. The old term for double digging is bastard trenching, because you have to convince some poor bastard to do it. If you feel the need to get some exercise, do something which will actually help your poor abused body like taking a walk or riding a bike.
You are not a beautiful and unique snowflake (sorry for the gratuitous Fight Club reference). I can assure you that what I am suggesting will work absolutely anywhere. The process I lay out is so easy, you can test it with half of one bed for comparison without killing yourself. I inadvertently split tested this three times over the years in three widely differing climates and soil conditions because I bought into the holy writ of double digging. Each time I double dug about half a bed before I got disgusted and quit. The other half of the bed was done with some variation of the method described below and resulted in:
- Nearly zero freshly sprouted weeds
- No breakthrough weeds or grass
- Better overall vegetable production especially in the first several years
- Absorbed rain and irrigation water better and stayed moist longer after watering
The double dug portion resulted in :
- Massive fresh weed sprouting from disturbed weed seeds in the soil.
- Soil surface which hardened under rain to near concrete crust conditions that would then flood and dry too rapidly.
- Poor vegetable production for several years until the natural structure reestablished itself and additional compost applied to the surface restored the balance.
So what did I do instead? Simple:
- Mow or simply trample down any weeds or grass.
- Lay down four sheets of wetted newpaper.
- Cover with at least two inches of compost (more is better).
- Cover with one inch of mulch if you want to plant right away or two inches if you want to plant after a season has passed.
- That is it, no digging!
Wetting the newspaper keeps it from blowing around while you are laying it out and gets the disintegration process started.
Using a soil knife or hori-hori to pierce the bed after six weeks or so will help the new layer reintegrate with the soil below without destroying the structure. Don’t overdo it, just once every foot or so. If you plant the bed right away, using a soil knife to set out any seedlings will do this automatically.
Using homemade compost is better by far than anything you can bring in in a sack. I split tested this a couple of times as well when I wanted to get more beds going than I had compost to cover. Water absorption and retention was dramatically better with my own compost than the best commercial compost available. If you don’t have enough compost, then get one bed going now and start another when you have more finished compost. Worst case use the commercial compost for the bottom inch and your own superior compost for the top inch.
If you have lots of time before you need the bed, you can pre-prepare the bed by just mowing and covering with a foot of mulch. Wet well and ignore for a while. Eight weeks to a year later (depending on your climate just check to make sure the weeds and grass underneath are completely dead) you can rake the partly decomposed mulch aside to cover your pathways and lay down the compost and fresh mulch to form the new bed.
And finally, disturb the soil as little as you can. Every time you start digging in the dirt, you’re disrupting all those dormant weed seeds just waiting to come to the surface of the soil and get a little sunlight. The less you dig, the fewer weeds you’ll get. Note: completely weed filled, unmown lawn and weed free garden bed in photo.
Easy, simple, no expensive back surgery needed. You have protected soil structure and emulated natural fertile soil conditions. So what are you waiting for? Get out there and start practicing the No-Dig Heresy!
Saving the world one (no-dig) garden bed at a time.