TO DIG OR NOT TO DIG

The question I ask gardeners when promoting no-dig growing is 'why do we dig?' To loosen the soil for drainage and aeration is the first answer and to get rid of the weeds is the close second. Followed by, to let the frost in, to help get a fine tilth and to dig in organic matter. Many often say because they simply enjoy the exercise and it makes the garden look tidy, and some just look at you as if to say 'well how else do you think things grow?' Certainly according to Alan Titchmarsh and all the other TV experts, digging or ploughing is essential for the health of the soil and the plants that grow in it.

So then I ask, how is it the fertile plains of America that had supported life for thousands of years were transformed to a dustbowl in one generation of farming? To which usually something is muttered about soil exhaustion. And yet in nature, plants have successfully evolved over millions of years in self perpetuating soils. How can this be?

Yes, it is true; most plants require well-drained and aerated soil since they feed via water and air. Compacted soil does not allow a flow of air and water between the soil particles, and makes root growth difficult. So you dig or plough to loosen the soil and bash it about to produce a crumby texture ready for planting. But hold on, what's causing the compaction? Squashing the soil, whether by foot or tractor tyre, is one cause. The biggest compaction however comes from the elements. Heavy rain on bare earth causes saturation and clogging of all the natural aeration channels and air pockets in a 'silting down' effect. Unable to absorb the downpour (a dry sponge can't absorb as much as a damp one), water runs off the top to the nearest low point taking 23 billion tonnes (world wide) of eroded top soil with it each year. The sun comes out, evaporating most of the rain, sticking soil particles together into big lumps and creating deep cracks. Gardeners and farmers look at this rock hard soil with perennial weed roots embedded with dismay and reach for the herbicide and machinery. Or else, they reach for the fertiliser to enrich the washed out earth in areas with sandy thin soil.

So in actual fact exposing the soil actually causes compaction. Nature covers up her soil in an annual mulch of decaying matter and a living shelter of green stuff. A layer of composted material on the surface will absorb 69% of rainfall and expands like a sponge to hold it. The same compost beneath the surface is compressed and cannot swell up to hold the same amount of water.

Natural aeration and drainage channels are protected from flooding with a layer of mulch. The worms and other crawlies can carry on their day and night tilling of the soil. These workers are natures diggers and fertilisers; just look at these interesting 'worm' facts:-

15 tonnes of leaves per acre per year are pulled down by worms in healthy soil

Worm casts contain 5 times more nitrogen, 7 times more phosphate, 11 times more potash, and many more trace elements than the surrounding soil due to the work of their gizzards. (Worms produce fertiliser!)

In good soil and properly fed, worms can produce 10 - 15 tonnes of worm casts per year.

Amazing! So anybody out there still chopping worms with their rotivators? Exposure to light and frosts will drive worms from the surface where most of their 'work' occurs. Also driven down by frost are the bacteria that live in the top four inches of top soil. Vital to the breaking down of organic matter, their work is suspended if they are forced deeper by frost or by soil inversion. Likewise the intricate threads of fungi that penetrate the soil are knocked back every time the soil is disturbed.

I'm sure all GGA readers are aware of the importance of mycorrhiza but for the benefit of recent subscribers here goes. Mycorrhiza are a symbiotic fungi organism that live on plant root hairs. They break down soil molecules into plant food molecules in return for energy supplied by the plant. Without the presence of mycorrhiza plants can't eat properly because they can only absorb water soluble nutrients in the correct format (like us eating calcium carbonate instead of calcium from food sources - totally useless, we weren't designed to eat rock). Plants then become minerally deficient and with their immune systems weakened they become prone to disease. And of course if you haven't guessed, mycorrhiza are killed by exposure to light by tilling and to chemicals.

So where are we? By digging we are hoping to create soft friable well drained soil, full of nutrients, with organic matter dug in. What you are actually doing is destroying the natural eco-system in the soil that is trying to do this for you despite all your well intentioned efforts. Of course many conventional growers do have successful gardens and farms and tilling the soil will produce a flush of fertility due to the nutrients released from decaying micro-organisms. Common sense suggests this is a depleting cycle that will eventually ruin the life of the soil and require the need for continual fertilisation, either by chemical or organic form. Nothing can replace the life-giving qualities of the soil’s eco-system and the natural health of the plants, and those eating the plants, will diminish.

So following the same line of argument, are we creating more weed problems by our efforts to eradicate weeds by digging? Let's look at what nature is trying to do with a bit of bare soil. Newly disturbed ground quickly germinates with seeds blown in or brought to the surface. Fast growing creeping things start spreading; docks and dandelions send tap roots deep to the subsoil to bring nutrients up to the surface. These quick growers, flower and seed in a rapid turn around of maybe six weeks to kick start the race to cover up. Next come the brambles and shrubby trees - elder, alder and hawthorn for instance. These fruiters feed the wildlife and start to build up the fertility big time, mulching the soil and creating 'nursery' woodland. Short-lived trees like larch, hazel and birch arrive and extend the eco-system until eventually a mature forest can appear with the long-lived trees, like oak or beech, finding fertile ground for their slow cycle of seed dispersal (around 50 years maybe from seedling to acorn producer).

This is the force we wage war with every time we expose the soil and try to keep it weed free. For us to live completely within our natural place in this system we should have to become hunter gatherers in that mature forest. Clearly we cannot do this, but we need not do battle with nature in order to live. Respecting and emulating her principles may be to our own advantage too; maybe we'd actually learn something!

So how can we do it? Basically we need to keep the soil continually covered by growing plants or else copy the autumnal principle of mulch, mulch, mulch! If we don't want weeds to creep in we have to give them no bare soil to colonise. Also to minimalise the need to disturb soil by sowing and planting out we should maximise the use of fruiting bushes and trees and perennial plants that can be harvested again and again without digging up the roots. Also we clearly want to avoid compacting the soil by treading on it so most non-diggers use a bed system.

So now we get on to the tricky subject of compost! If any of us could produce enough of the magic stuff to give a permanent two inch layer on our beds we'd be laughing. Personally I can't so I tend to manure every 3 or 4 years and in between I use anything I can get my hands on to mulch - lawn mowings, collected leaves, weeds, shredded garden prunings, comfrey and dandelions grown for mulch, ornamental grasses harvested for straw, other people’s unwanted green waste and mowings. I also use green manure on bare patches in the winter and allow undercrops of weeds beneath tall plants (eg chickweed underneath broad beans, horsetail under sweetcorn).

I compost my kitchen waste with leaves, comfrey, nettles and cardboard but this is never enough so I tend to only use it around the roots of transplanted plants or for sowing seed into. For sowing fine seed I sow into a line of compost and cover the space between rows with mowings (produces lovely stripey beds!) For big seed I lay the seed on the surface and cover with mounds of compost. Bare soil is my guide - if I have a bare patch showing through and a half rotted compost heap I would rather empty the heap.

Here's something to think about though. I've recently read that decaying waste requires quite a bit of nitrogen to break down and therefore by not composting first you may be leaching nitrate out of the soil and inhibiting plant growth. I certainly have found that scraping back unrotted mulch, especially high carbon stuff eg 'woody' things like straw, and sowing directly beneath tends to affect germination. Also I can see how digging in unrotted matter could be harmful (it goes against nature anyway) but leaving it on the surface around well establised deep rooted plants must be a natural process surely? Ensuring the good fine compost goes around the roots and stems of seedlings and thereby mimicking the natural process of seeds germinating in the spring on compost formed over the winter intuitively 'feels' OK to me. Any thoughts?

To me, no-dig gardening is more than just continual mulching! Companion planting, wildlife planting and even moon planting are just as much part of the process of creating and encouraging a natural eco-system to build and interweave a network of support and exchange in your garden. I like to think my efforts to regenerate this on my allotment mean I'm actually slowly becoming part of the system too!

Alison Ensor

References:-
Gardening Without Digging - A Guest
The Lost Science of Organic Cultivation - SA Howard and R Krsna Das