7 Mar 2016

Dig or no dig, soil has the answer

Ardd Fotaneg · Botanic Garden

I recently shared a post for a no dig gardening talk on Facebook and it reached more people than any of my other previous posts. It is obviously a topic of interest among gardeners and growers but why?

Why We Dig

Gardeners of old love to dig but is it really the best thing for our soils or our backs? There are many reasons for digging. It is a tradition on the allotments keeping the old allotmenteers busy through the cold winter months. The nation even rallied round to ‘Dig for Victory’ during the Second World War.

Compaction and Aeration

Digging alleviates compaction. Heavily compacted soils contain little space between soil particles. This can result in poor drainage from the compacted layer. Good drainage is important to prevent soil saturation and water run-off which contributes to flooding.

Digging can help to aerate Soil. Soil needs aeration to allow oxygen and vital nutrients to efficiently reach plants’ roots. Beneficial micro-organisms found in soil also need air for respiration and metabolism.

However, over digging can put too much air into the soil. This can provide an unstable footing for plant roots. Over digging can also damage soil structure. Digging can disrupt the balance of particles and space already in the soil.

An alternative ‘no dig’ way of relieving compaction or aerating soil could be by using plants. Annuals and biennials with deep tap roots are perfect for this. Common teasel Dipsacus fullonum is a native biennial so it dies in its second year.

Teasel produces a large tap root that will grow deep into the most compacted soil. As the the root dies, it shrinks creating air pockets.

Vegetables also have the ability to delve deep into the soil. I’ve grown successful parsnips with long roots on heavy clay with minimal soil preparation.

Organic Matter

We sometimes dig to incorporate organic matter into soil. Organic matter provides nutrients for plants and other organisms in soil. Organic matter also acts like a sponge, with the ability to hold water. Soil with good structure needs minimal input of additional organic matter.

Adding too much manure or compost to the soil is wasteful and can lead to the run-off of excess nitrogen into our waterways. Not to mention that it’s hard work.

Digging increases oxygen into the soil. This speeds up the breakdown of organic matter. This can lead to impoverished soil and the need to incorporate even more organic matter. And even more unnecessary hard work.

Referring back to our ‘no dig’ teasel: when the root dies, it slowly breaks down in the soil. This increases microbial activity in the soil. Resulting in less compaction, more organic matter, nutrients for plants, happy micro-organisms and no bad back!

‘No dig’ Green Manures

Green manures such as alfalfa Medicago sativa which has deep roots can help to improve soil structure and add organic matter. However, to be effective in a ‘no dig’ system it will require a couple of years of complete light exclusion to kill it off.

Annual green manures such as Phacelia tanacetifolia that die off in winter are a better alternative. The cold winter kills the plants. Left on the surface of the soil, it slowly breaks down over winter. Worms and other soil fauna help to break down the dead foliage. As their numbers increase, the soil becomes better aerated, without having to dig it. The soil can then be directly planted into in the spring. This way of fertility building on the surface of soil instead of digging is a natural process.


Mulching is a technique used in ‘no dig’ gardening. A mulch is a material that is spread on the surface of the soil. You can use decaying leaves, grass clippings, straw, bark or compost. This winter, our vegetable gardener, Blue, used spent hops from a local brewery to mulch beds in the Double Walled Garden. The mulch helps to protect the soil from heavy rain and from drying out. It also helps to suppress weed growth.

As the mulch breaks down, it adds nutrients and organic matter to the soil. It encourages beneficial micro-organisms that help to keep soil healthy. It also provides habitats for beneficial insects such as ground beetles providing a balance in biodiversity.

Applied annually to the surface mulching requires no digging. With ‘no dig’ methods there is little disturbance to the soil. This means that fewer weed seeds are brought to the surface, and fewer weeds means less weeding.

Raised Beds

Raised beds are perfect for ‘no dig’ systems. Build them small enough so that you can reach the centre without treading on them. For the ultimate back-pain-free gardening, build your beds high without the need to bend.

In the Growing the Future Garden and Canolfan Tyfu, we have some excellent examples of raised beds.

I’m a big fan of the ‘no dig’ system. I like to see the joy on people’s faces when I tell them that digging isn’t necessary. I also like to think I’m helping the planet by practising sustainable horticulture. It seems like a win-win situation for all.