Monday, 25 March 2013

Garden myths discussed: You need to dig the soil to aerate it


Perhaps my previous title ‘Garden myths debunked’ was rather pretentious but I felt  inclined to retain it for this one! It is so contrary to what I as a no dig gardener believe! It then occurred to me that in some circumstances it might be true! Can it really be, that some gardeners abuse their soil so much they need to cultivate to aerate?
In fact, clearly any cultivation aerates, but is it necessary, what does it do and is it desirable? In one sense  aeration that promotes the breakdown of organic matter is part of the traditional gardening and agricultural scheme as I discuss in this previous post. 
My argument is that nature aerates her undisturbed soil without the need  for any mechanical aeration. We will turn a blind eye to errant moles and rabbits!


The rabbit subscribes to the theory of aerating and like many gardeners likes to ‘show off’ the crumbly soil, thereby starting the process of the soil’s structure destruction! Fortunately I can kick back this soil and tread it down. This great hole in my herbaceous border is causing less plant damage than the digger who digs around the plants.
It’s the wrong type of aeration 
Sometimes I read that I should dig the soil to aerate it. I get quite cross. It’s not that there are not legitimate reasons to dig, better gardeners than me dig. It’s just the reason given! 
I know the railways protest “it’s the wrong sort of snow”  and now its my turn, “it’s the wrong type of aeration”. When a soil is energetically cultivated the natural internal structures are ripped apart. Apart from destroying natural cracks and channels that provide drainage and aeration, soil aggregations - intimate mixtures of organic materials and particles -  are exposed to the elements. The soil is aerated, it is super-aerated and organic matter is oxidized away. An undisturbed natural soil delivers essential oxygen to soil life in a much  gentler, kinder and controlled way. 

No comment!  Location withheld to protect the guilty.
Aerating between established plants is a complete waste of time
It’s when I read I should dig the soil between my plants to aerate that I really go spare. 
Light hoeing is fine for weed control and I can even - with difficulty - tolerate a light fluffing through for cosmetic reasons. But digging, please no, and rotavating between nursery rows is quite beyond the pale. Don’t people know that churning the soil between growing plants is not only bad for the soil, it’s bad for the plants! Loosening the soil between plants does let in air, but it also cuts away any roots that might in theory benefit. Yes, they grow back, but what a waste of their energy, when they are likely to be chopped again. It’s interesting to ponder what induces roots to grow out into the soil. They grow towards air and they grow towards water (importantly, they do not grow towards dry conditions in search of water). Soil at the very surface is that which is best aerated and after rain is wet. Roots want to grow to the surface and not be chopped away.

It is ironic to think about herbaceous borders dug over in autumn when the soil later becomes excessively wet in winter, where the ground is badly drained. An elevated water table displaces oxygen and deep roots die. The ones at the surface have been cut off or damaged.The first spell of dry Spring weather the plant is dead. It’s not ill fortune that killed the plants. To paraphrase the ‘red tops’, “it’s the digger that did it”.

My ten year old herbaceous border has never been dug, even when planted. It was planted direct into glyphosate sprayed turf and for cosmetic reasons given a light mulch. Apart from small design re-adjustments and a little propagation, it has never been lifted and divided.
My the end of February it is time to cut  down. As the soil is undisturbed I can do this even after heavy rain. Even now the plants are free standing, although none have been staked.

Perhaps not your idea of tidy! In a few weeks there will be lush green leaves.

15 comments:

  1. Haha, my 23 year old borders have never been dug. I have a gardening friend who always digs between the plants in autumn. In spring she is complaining about loss of plants. I told her many times, but according to her she has to dig the garden before winter, otherwise she does not feel well....... So many men, so many minds. But in summer the same digging people ask how we manage to get such a nice borders.
    Your border looks great in summer and so do your grass, I cannot say that with a border collie making a race track of the grass.

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    1. Good to have the benefit of your experience Janneke. I love your english turn of phrase. I have friends like yours!

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  2. I'm not big on aeration either. I just dig holes, put the plant in and mulch. Seems to work for me.
    Cher Sunray Gardens

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    1. Thanks Cher. I think almost everyone who has a quality garden knows that this is how you get best results. I agree about the mulch.

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  3. Your summer border is a beauty Roger. The more I read and see about your no dig philosophy the more I am beginning to understand.
    My latest blog contains a method of soil aeration that you choose to turn a blind eye too!

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    1. Yes, your mole! What an amusing piece you have written about it on your blog!

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  4. Roger, presumably even if you don't lift and divide the plants you do cut down their foliage (as evidenced by your last photo). When do you do this? I mean, at what point in the year.. Autumn? Spring?

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    1. I cut down my herbaceous borders at home in January or February. I do also have lots of herbaceous plants on the village plot and in the two cemetery gardens. There I tend to cut back (with my petrol hedge trimmer) as plants start to become untidy and have nothing left to offer. This works out at me cutting back perhaps November to March depending on the plants -and my energy! Brenda insists I am rather tidier at home.

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  5. I once considered aerating the perennial garden but then thought...if it isn't broken, why fix it? Every year it returns lush and beautiful. Occasionally I'll move something here or there and divide to plant elsewhere.

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    1. Good thinking Carolyn. I do like you and occasionally move the odd plant to improve the design. I do not subscribe to the traditional view that herbaceous borders need replanting very three years! In fact although herbaceous borders have the reputation of being labour intensive I think the opposite and herbaceous perennials are my favourite plants.

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  6. The herbaceous border is lovely - you seem to have a decent sized garden

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    1. Oh yes Sue, just under an acre! I am longing to get in there when these cold winds subside. Why don't you come and see it for yourself on my open day in mid July- that is if you can tear yourself away from blogging and gardening!
      Actually fellow bloggers like yourself are welcome anytime.

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    2. I'll take you up on that when the weather improves - hopefully it should have by July!!!!

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  7. Dear Roger,
    I am fascinated by this. I have recently (last December) moved into a new build home with newly laid turf. I was intending to dig a large herbaceous border in one corner but having done some minimal planting in the front I'm aware that the soil I have been left with is very heavy shaley clay, with a very minimal amount of topsoil for the turf to root into.
    I was really not looking forward to digging it but I now have a glimmer of hope.
    I have 3 shrub roses to put in put the rest will be mostly perennials in 1-2 litre pots. Do you think this will be feasible?

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    1. Hello Mr or Mrs Quilter
      For me not only feasible, but normal.
      Give it a go. My latest post (before later today Ist sept) shows me planting Cathi's garden using exactly the same principles
      (My aunt lives in Sisters Oregan where they have a wonderful quilting festival)

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