Each autumn, there’s a collective, nationwide groan as gardeners think about the endless digging they’ll be doing over winter to improve their soil’s condition for the following year.
But Charles Dowding, renowned market gardener and expert vegetable grower, can offer them some good news.
Over the years, he has conducted many experiments comparing the effect on plant growth of digging with not digging and has found that a ‘no-dig’ approach is the way to go. It not only saves time and exertion on digging, but also on weeding, because far fewer weeds grow on undisturbed soil.
He insists that growth and quality are improved by simply covering beds with 2.5-5cm (1-2in) of compost over the surface.
“The usual recommendation is to dig or even double dig the soil for growing vegetables,” he says. “Because this is repeated so many times, most gardeners accept the task without wondering if it is really necessary. In fact, there is no need to dig at all.”
Initial clearance of weedy and grassy ground can mostly be achieved with mulches (such as cardboard and compost) and some digging out of woody plants, then you can maintain the plot by weeding regularly. Surface compost weathers to a soft mulch over winter and can be directly sown or planted into, he adds.
“Soil does not need to be mixed, stirred, scraped or tickled. Only large lumps of organic matter on top require some knocking around with a fork or rake to create an even surface, mostly in winter and spring.”
Dowding has run an experiment since 2007 to understand the effect on soil of digging and not digging, comparing growth of the same vegetables growing side by side in dug and undug beds.
“In the absence of digging, I have found that harvests are as high, sometimes higher, while some extra quality of growth on undug soil may be apparent.
“Soil in the undug beds, with compost on its surface, is well-drained, retains more moisture in dry springs and grows fewer weeds and stronger vegetables, especially at the start of the season,” he explains in his new book Veg Journal, which offers month-by-month no-dig advice.
A key point in the no-dig approach is that undug soil is firm, which is not the same as compacted; roots have freedom to travel and are well-anchored at the same time.
“Fertility is enhanced by an increase of undisturbed soil life, which mobilises nutrients and helps plant roots to access them,” he continues. “This is most noticeable in early spring, when growth on undug soil is generally faster by comparison with dug soil, whose fertility, in terms of soil life, is still recovering from the winter digging.”
In experiments he found that during spring and early summer, many vegetables on the dug beds, especially radish, onions and spinach, started growing more slowly, and that in the undug beds the leaves of spinach and lettuce were thicker and glossier, the radish roots were shinier and the onions had a deeper colour.
He says that firm soil is often wrongly labelled as ‘compacted’, yet soil which has been mechanically loosened and fluffed up is not stable, which is why you have to walk on planks after digging heavy soil to avoid compaction.
Compacted soil is squishy when wet, rock-like when dry, contains few or no worm channels, is hard to crumble in your hand and may smell sulphurous because of lack of oxygen. It usually happens in the top 15-20cm (6-8in) of the surface and if it does, he advises adding plenty of organic matter.
He concludes: “My advice is simple: disturb your soil as little as possible.”