September 19, 2014

The Darker Side of Digging

Feeling warm and slightly out of breath you stand up and have a stretch.  Time for a cuppa.  You park your spade in the freshly dug earth and reach for your thermos.  You feel a warm glow inside as you watch the robin looking for worms in the soil.

You admire the square of soil that you have just spent the best part of an hour digging.   A square of lovely dark, grey, weed free soil to your credit. Good, honest work that.  Getting close to the earth, close to nature and getting some exercise in the process, that’s what life’s all about.  All is well with the world after a spot of heavy digging with your trusty spade, followed by a nice tup of tea…..

All is not what it seems

Um, I think I might be about to shatter your illusions here.  You see digging is not the ‘salt of the earth’ pursuit we might have been led to believe….

You see digging the soil and removing the weeds that are currently covering your beloved patch contributes to the dreaded greenhouse gas, carbon dioxide.  How?  Well, if you remember the carbon cycle from school?  No?  Well, basically plants take up carbon dioxide from the atmosphere through photosynthesis and convert it to energy.  The carbon ends up in the leaves, the stems, etc and the plant emits oxygen.  We all know that this is the only way that oxygen is created on the planet – by photosynthesis of green plants.

So what happens to the carbon – well, when the plant sheds it’s leaves or dies it rots down into the soil, generally adding to the organic matter. That’s organic as in ‘carbon containing’.  Great.  The soil acts as a great big carbon dump, locking the carbon in…..until we dig it over, or remove the pesky nettle patch.

Bare soil exposes the carbon locked within it to oxygen present in the atmosphere.  The carbon and oxygen combine and, you’ve guessed it, you end up with carbon dioxide being produced.  Now, I know that your little square of bare earth isn’t really going to make a whole lot of difference to the general ‘look at how much greenhouse gases we are producing‘ globally, but get this, according to the soil association:

“Soil carbon losses caused by agriculture account for a tenth of total carbon dioxide emissions attributable to human activity since 1850”

Wow.  So it’s not just us gardeners who are to blame, it’s the farmers as well. Sheesh.

Hooray for the lazy person!

Merrily digging away can also:

– Potentially damage the topsoil structure, upsetting the balance of those delicate symbiotic relationships that keep your soil healthy.

– Bring to the surface dormant seeds that have been lying in the subsoil for some time, thereby adding to your weed problem, if, indeed it is a problem.

– Displace valuable nutrients, pushing much needed organic matter deeper into the soil where it can’t be accessed by your veg.

Or maybe not

So yay to the ‘no dig’ brigade.  Yes, well, maybe.  To play devil’s advocate there is also a school of thought that reckons the benefits of not digging are only for the short term.  The much respected John Harrison for one.  (Do please check out John’s site, it’s the best allotment site on the web, with the friendliest and funniest forum I have ever seen).  John is convinced that not digging at all will result in a compacted soil layer a couple of feet into your soil, resulting in long term loss of fertility.

If he’s right,  what’s the answer?  We’re stuck between a rock and a hard place aren’t we?

 Mix things up a bit.

I think (and yes, I’m biased here) that the answer is simply to plant different stuff together.  You won’t get a soil pan if you have roots that go down a really long way.  Interplant deep rooting plants with your carrots or salad.

For example, take perpetual spinach, those roots are enormous.  The first year I grew them I tried pulling them out by hand once they’d gone to seed.  Much to the amusement of my more experienced plot neighbours!  Plant your shallow rooting stuff around the base of a shrub and it’s even better.

The whole dig or not to dig debate isn’t relevant if you don’t do neat rows of single types of veg in your patch.  You know, do away with the veg patch idea altogether and plan your edible plants to fit with your ornamental garden.  There’s bound to be trees, shrubs and perennial plants there, all with different types of rooting systems.   Of course if you are not growing your food on a yearly basis and go with more permanent, perennial type planting then so much the better – forest gardening wins again!

Check out the soil association article on carbon and organic gardening here.

Photo credit: hughrocks / Foter.com / CC BY-SA