It is amazing how many gardeners still believe a regular dig each year is essential. Some may prefer autumn digging, others later, some do deep digging and others just surface forking over. I've been a passionate no-digger for decades and can't see the point of annually digging every vegetable plot from one end to the other. Indeed it may surprise you to learn that all of my forty vegetable beds have never been dug as such over twenty years and that most were never even dug over initially!
Of course at first a good dig seems important, initially, after all no-one knows what debris lies hidden under a skin of weeds, it helps level the ground and presumably one might also want to incorporate compost and manure while digging. However although the first point has merit the last fails. Truly the old bicycle wheel, tin cans, bricks, broken glass and stones and are best evicted however this can occur piecemeal later. Likewise weeds do not have to be evicted to be killed and levelling can be accomplished more slowly. Importantly compost and manure and so on applied uniformly to the surface soon disappears. It is on this last property that most of the no-dig philosophy rests.
Mulches have many different effects on the soil. They alter the soil temperature making it slower to rise and fall. Mulches generally keep the soil moister by preventing evaporation -though some waste light showers by trapping the rain in surface layers merely to evaporate away and so never reaching the soil underneath. Similarly thick mulches may restrict soil aeration especially if they pack down though coarser ones cause little problem. Thick mulches prevent seeds in the soil germinating. Mulches break the wind, heavy rain and sun stopping them concreting or eroding the soil. And most importantly organic mulches break down adding to the soil fertility and humus fraction.
This property of surface applications breaking down and disappearing into soil fertility and humus is believed to do more for the soil texture, aeration and drainage than an annual dig incorporating those same materials. Of course if you enjoy the exercise do not let me stop you as it is far healthier than visiting the gym. However I reckon the same effort applied to collecting compostable materials, composting them, mixing the heap, and sieving then applying that material will give even higher returns.
The no digging argument goes that there is little soil disturbance similar to digging in nature save after catastrophes -and by creatures making burrows and nests. Worms are reckoned to bring up a dozen tons of casts per acre per year but from all levels. Moles, rabbits, ants and others may do likewise. However there is no wholesale digging up, turning over and leaving bare the top foot or so save perhaps if many trees uproot together. Such spontaneously revealed spots are rapidly colonised by plants with long-lived or airborne seeds and which are the antecedents of most of our garden weeds. In nature the rule is for plant life to cover every bit of bare ground as soon as possible.
This may not happen at ground level, in a beech wood or under any dense trees especially evergreens the leaves exclude so much light few plants exist at ground level. But the soil is covered both by the canopy and again by a litter of twigs and leaves. The two together prevent heavy winds, baking sun or driving rain from eroding, packing or panning down the soil which is also bound by the networks of tree roots. The soil may be thin but thus protected it teems with life and rapidly recycles the trees' nutrients back to them. Where trees and woods are removed, say with grazing animals or regular fires the soil becomes covered in grasses in the temperate zone, with heathers in poorer soils. These still cover the soil with a litter of leaves and bits but now it is on a finer scale though still functioning in the same way. When we reduce our ground to bare soil it is no longer fixing sunlight binding that with water and soil nutrients into forms of life and future fertility. Instead it is likely to erode or pack down into cement like dried mud. Improving the humus level improves the crumb structure and the bare soil can resist erosion and packing for longer. Fill the top soil with fine roots and it is better still. But add some litter and suddenly it is much more stable, deeper, moister and more fertile.
The no-dig argument thus maintains that a healthy soil needs a litter of some form on top lying underneath and around most plants. Furthermore that this litter can then, thro' the agency of worms et al, greatly increase soil fertility and that using such far outweighs any alleged benefit obtained by simply digging the soil. Obviously diggers imagine that all those benefits and more could be had if the litter was just applied after a good dig.
However no-diggers believe the natural networks of worm holes, decaying roots and soil fractures allow for more soil aeration and drainage than does the structure of any homogenised soil after it's been dug over. Furthermore no-diggers reckon that it is also important not to disturb the different soil layers as each has it's own mix of inhabitants. Most of all no-diggers point out that digging is done in the winter so the soil can recover by spring -because undug soil has better capillary networks and draws up water more easily than does loosely dug soil. The proof of this is if you dig over a bed well and rake it down to a fine tilth. Then walk across it. The next dry day the surface soil will be dry except in your footsteps which will remain damp -your weight consolidated the loose soil to form a capillary network. (Faulkner, mentioned in the booklist, deliberately station consolidated his soil at immense pressure in order to get good capillary networks.) On the other side diggers justify digging for many potentially valid reasons; it can more rapidly obtain a level bed for cultivation, it can incorporate a flush of weeds or a dose of manure, it exposes pests to the birds (what percentage must be debated), it aerates the soil, breaks up pest nests and tunnels, and rather erroneously 'lets the frost break the clods into a fine tilth' (the frost may just as well break up a surface layer of soil into a fine tilth). Most garden books still subscribe to a dig annually in the vegetable plot (surprisingly it was also the custom to annually dig over herbaceous and shrub borders, and even digging over the soil around tree and vine roots before repacking.
So has any trial been done; well many, including several by the HDRA. I myself set up a trial when I came here to Dickleburgh with nine of my forty 5foot by 15foot beds being dug over each by different degrees and with different additions of turf, compost and manure and one converted by mulching with carpet. Having seen the first year results the remaining thirty were managed by killing the top growth with weed proof mulches of carpet (now not recommended) laid over the turf with some compost and manure spread about beforehand. Once the original growth was killed off by the carpet the paths were dug out and spread on the beds levelling them and creating a tilth in one go. Over the first ten years I was convinced the dug beds had a poorer texture and were not as productive as the undug. Moreover I could never have dug over the huge area I took on anyway. To this day the whole forty have never been dug.
Overall most advocates suggest that an initial dig is worthwhile especially in heavy and badly drained soils, some maintain that it is better to retain the layers undisturbed but then you need to gain weed control by other methods than digging the roots out! Thus plastic membranes or herbicides become necessary. The trials then show that there is some small benefit to digging every seven years or so. However this gain is not huge and usually smaller than say the benefit from one really good watering in an average growing season. The reason is that although any soil may benefit from occasional disturbance this is least value in the vegetable bed because there the soil is usually already amply disturbed. In most vegetable plots most gardeners employ a rotation and grow potatoes and or root vegetables such as carrots and parsnips. With these crops coming around every few years their soil manipulations whilst growing and harvesting more than compensate for any need for annual digging. It would seem that our digging may be better devoted to working over the fruit cage's soil every seven years than annually that of the veg. bed. Bibliographical evolution of the main No-dig argument
18C 'Substitute for manure' Jethro Tull -in this he expounded the converse -he valued regular and frequent soil pulverisation as he believed this produced fertility (partly true-increased aeration and decreased particle size will give short term increases in fertility but at the cost of long term impoverishment). 1945 'Ploughman's Folly' Edward Faulkner an American farmer (also 'Soil Restoration' 1953) reasoned in favour of minimal disturbance and indeed soil compaction to restore capillary network. 1944 'Gardening with compost' F.C. King gardener at Leven's Hall near Kendal in this concentrated on the value of mulches for improving soil health and fertility and later put the argument for not digging in his later 'Is digging necessary?'.
1947 'Gardening without digging' A. Guest of Barnsley puts forward not digging by means of mulching the surface with compost and is convincingly practical. 1950 'Organic Surface Cultivation' Gerard Smith advocates not digging by mulching combined with surface cultivation. Convincing on ornamentals and fruit he's a bit dubious in the veg. plot. 1960 'Successful gardening without digging' James Gunston a pragmatic private and market gardener is convincing on both fruit and vegetables without digging but drags stuff about with a crome (huge coarse rake like a bent over fork).
1963 'Cut-work gardening' Shewell-Cooper who founded the Good Gardeners Association at Arkley Manor though heavily into mulching was not-digging elsewhere but still rather on the side of digging in the vegetable garden, and with a powered cultivator for ease, but by 1976 in his 'Mini-work gardening' he had become persuaded of the No-dig method and advocated it strongly. 1969 'N0-digging report no1' HDRA while still at Bocking, Essex reported on several methods; including JLH.Chase's seven year trial at Chertsey, the Veganic O'Brien system as put in 'Intensive Gardening' by R O'Brien and The Ruth Stout system in her American 'Gardening without Work'.