In the autumn it is common to see people on allotments from Lands End to John O’Groats doing the backbreaking work of annual digging. It is traditional to dig vegetable gardens every year, but is it the best way to manage the soil? During the last few years there have been increasing arguments about the value of digging. The enthusiasts argue that annual digging is the best way to remove weeds and revitalise soil. The counter argument is that digging damages soil structure is a waste of energy and makes life more difficult for the gardener. So who is right?
Digging has always been part of the ritual of gardening and it is difficult to argue against what appears to be such a ‘natural’ activity. Go to an allotment at any time of the year and there will be people digging. Walking down the track to my own plot last November I was greeted with a hearty “done yourdigging yet?”
The case for regular digging is that it is a good time to remove weeds and loosen soil that has become compacted by foot traffic and weather. It is physically demanding work that has finished off many a good gardener by giving them a ‘gardener’s back’. There are also many prospective vegetable growerswho are put off by the idea if digging the plot over and over again. It does not have to be like that, there are alternatives.
Is annual digging the best way to manage soil, particularly heavy clay? Consider the action of digging to one spade depth. On shallow soils it will expose sub-soil and bring it to the surface. At the same time the fine top soil is buried. Even if your top soil is of a reasonable depth why bury the top few inches which you have worked so hard to get into good condition?
Then there is the practice of digging in large quantities of manure in the autumn and leaving the soil exposed all winter. Rain not only compacts soil it also washes out nutrients supplied by the manure, particularly nitrogen. Where do the leached out nutrients go? Into the water table or downthe local stream. Pollution from ‘natural’ manure is just as damaging as that from the synthetic alternatives and manure should be applied when it is needed and not as an annual or twice yearly habit.
In the spring its time to dig again, or use the rotovator which is even worse! Rotovators certainly break up the top soil, and are an easy way to produce a fine tilth, but they can also damage soil structure. The blades of the many rotovators are ‘L’ shaped. The part that is flat on to the soil polishes it as it rotates a few inches below the surface. This makes an impermeable ‘pan’ which can produce poor drainage and even water logging of the top soil. It also means that roots have to make an extra effort to penetratethe hardened layer. Rotovating in spring is often accompanied by the application of another load of muck. You will hear gardeners say that the ground is so hungry it has to have another feed as it’s the only way to get decent crops.
An alternative way of managing soil is becoming increasingly popular and is known as ‘no dig’ or ‘minimum tilling’. The no-dig garden is divided in beds, usually 1.1m (4ft) wide which makes them easy to reach from the sides. They are prepared by an initial double digging and incorporation of bulky organic matter. The soil is later worked down to a fine tilth. Once dug the beds are not walked on, this avoid compaction from foot traffic. The beds are also covered as much as possible by crops, green manures and mulches to avoid compaction from heavy rain. Covering the beds also helps to reducenutrient leaching by rain or snow.
In no-dig gardens organic matter and manures are applied as surface mulches in the autumn or while crops are growing if extra nutrients are required by heavy feeders. This works well on clay soils but on very light soils it might not be possible to incorporate enough material without cultivation. Theanswer, in this instance, is to incorporate manure into the top few inches with minimum soil disturbance.
Using the no-dig method of gardening provides some interesting ways of growing crops; potatoes cannot be earthed up in the usual way but are grown on the surface and covered with a straw or other mulch. This makes it very easy to harvest the crop as all that is required is to remove some of the mulch, pick up the quantity of potatoes required and replace the mulch.
There are other very good reasons to limit the disturbance of top soil. Over recent years research has been carried out into the bacteria and fungi that live in soil. We all know that there are some nasty fungi around, things like clubroot are rife on many allotments, but there are also many beneficialfungi that work with plants.
Mycorrhizae are a type of fungus present in most soils; they live by attaching themselves to the roots of plants. The surface area of the fungus is very much greater than the area of the roots so the fungi effectively extend the feeding area of the plant. They work in harmony with the plant by helping it toabsorb more water and nutrients, in return the plant provides food for the fungus.
Having such helpful fungi in the soil is of obvious benefit but mycorrhizae are fragile, they prefer soil that is not disturbed so thrive in ‘no dig’ gardens with a high organic content. Although naturally present in soil the numbers can be boosted by adding an innoculant. This has been a fairly common practice in the US but commercial innoculants have only recently become available in the UK.
Another major benefit of not digging is the decrease in the number of weeds. Every time you turn over soil more weed seeds are exposed to light and can germinate. Some need only the merest flash of light to wake them up and start growing. After a while no-dig beds have fewer and fewer weeds until eventually there are hardly any at all!
After many years my no-dig beds continue to support a thriving plant population. The beds have not been dug for at least 5 years and yet show no sign of being compacted or exhausted. The regular application of garden compost and mulches has produced a loose, friable top soil that is easy to manageand virtually weed free. A word of warning; a couple of years back a neighbour kindly donated several sacks of well rotted horse manure. I used them all on the beds and grew a good crop of weeds including nettles, docks and grass! Now I use only my own garden compost and leaf mould.
The no-dig technique
- Start by double digging your beds making them around 4ft (1.1m) wide.
- You can edge the beds with timber if required but do not use pressure treated wood as there is some belief that the chemical used can leach into the soil.
- There are recycled plastic alternatives.
- Do NOT walk on the soil again, even using boards.
- Keep the soil covered as much as possible to protect it from heavy rain which causes compaction.
- In Winter use green manures, mulches or garden compost covered by black plastic to protect the bed from the worst of the weather.
- Make paths around the beds at least 2ft (75cms) wide. They can be covered with a permeable membrane, chopped bark or any other weed suppresser.
As far as I can see there is no need to dig your plot every year in fact it can do more harm than good to both the garden and the gardener. If you want the exercise then there are other ways of keeping fit most of which are better for your back! Why not have a go at not digging this year and see how it can work for you.
Update 8 Feb 2009
I used no-dig with great success for many years. When the new garden was started in 2003 I again opted for the same approach as a way of managing the very heavy clay. It worked well for couple of years but after the re-occurrence of a serious health problem, autumn of 2005 we moved to a modified no-dig, or ‘minimum till’ as it is called in the US.
Now we use well rotted cow manure and a small rotovator. It is a Honda that has star shaped tines that are not bent to an ‘L’ shape. This avoids the polishing of the clay that produces a hard pan in the soil. We still avoid walking on the soil as much as possible and keep it covered in winter to avoid rain compaction.
Overall the results have been very encouraging. The muck has really increased the organic matter and fertility; the crops in 2007 and 2008 were superb, the best ever! I am not saying that no-dig does not work, it clearly does. What I am saying is that it can be modified to suit circumstances. I came to the conclusion that it was better for us to use cow muck and a rotovator than give up, or seriously reduce the amount of food, we could grow.
