Wednesday 27 November 2013

Why gardeners dig: to sever unwanted roots

My posts in this series explore why gardeners cultivate the soil. In some cases I carry out the same cultivations myself. In other cases I do not share gardeners’ methods but appreciate their good reasons within their system of management to do so. In the case of deeply cultivating amongst established plants I firmly disapprove. Today I shall sit on the fence!

Protecting my allotment

Many years ago I had an allotment. It was a long strip of ground alongside a private garden. I have boasted in a previous post how my none dug soil was black with organic matter and highly fertile. One day I went down to my allotment and found to my complete devastation that my neighbour had planted a leyland cypress hedge on his side of the boundary! I sulked for a week! That wretched plant, would suck my beautiful soil dry of water and nutrients, not to mention stealing my light if it was allowed to  grow high.
I resolved every couple of years to dig a two-spit deep foot-wide trench on my edge of the boundary. I have no idea if cutting the hedge roots did much good to my garden but I felt  better for it. Although perfectly legal, in the interest of neighbourly relations I waited until my neighbours were out!
It did not appear to do the hedge any obvious harm. Unfortunately.
I never quite determined  how many cypress roots  grew up from depth into my plot!

My present undug vegetable garden is lined with a 1.5 m.privet hedge separated by a 1m path. I no longer dig a trench! There is a small but not very significant fall-off in the quality of my plants near the hedge. 

Planting under trees

Most of my ‘other’ gardens are rather well wooded. I frequently plant under trees in my cemetery gardens. Other than making a slit or a small planting hole I never dig. Planting some times almost breaks my wrist. It would be impractical, time consuming and in my opinion, a waste of my energy to dig in any conventional way. (And in an old cemetery one might not be quite sure what you might dig up). Undoubtably there is competition to plants from tree roots. 

Nature faces this problem of competition all the time and plants have evolved  to compete.The natural ecology of an un-dug soil is such that woodland plants are well able to grow under trees. There are factors such as existing mycorrhiza, natural cracks where dead tree roots have decayed away, mulches of leaf litter and all the benefits of earthworms.
I would argue that digging such a soil, although it would make the process of planting much easier would in the long term be detrimental. Tree roots are amazingly quick to recolonise and exploit new loosened soil. I shudder at the thought of all those  water-hungry exploring young fibrous tree roots competing with my plants.

As a contrast to my more natural planting, I have in my minds eye, a picture of Victorian parks (no I’m not that old, but you know what I mean), where walks under trees were sometimes lined with borders of bedding plants. Because of aggressive invading tree roots they were dug every year.

Good gardening reasons for cutting roots

  • Undercutting nursery stock. When nurseryman grow ‘open ground’ shrubs and trees to ensure a compact root system they routinely undercut the plants with mechanical equipment. On a small scale it can be done with a spade.
  • When planning to move a well established shrub or small tree it is sometimes  good practice to anticipate the event by severing spreading roots several months before the operation. Some gardeners dig a trench around the plant and back-fill with fibrous material to encourage new compact peripheral roots. (I also firmly recommend reducing the tops when moving old plants).
  • Root pruning is a traditional and very effective way of keeping vigorous plants smaller. Think of bonsai!
  • There is increasing evidence that when transplanting trees and shrubs that if distal roots are damaged it is best to cut them off and let the more central healthy roots regenerate.
  • Although I do not transplant my own leeks many gardeners do and ‘top and tail’ them. It goes against my own instincts but it is common practice.


  1. For 20 years I dug up the vegetable garden but 7 years ago we moved and I adopted the no till method. The soil in the new garden a a good deal poorer than in the old one but putting a layer of leaves each autumn and not disturbing the soil has already made quite a difference. When you look at nature, most plants don't get their soil dug up. Weeds seems to be the only ones to benefit a lot from tillage.
    I have a hedge that produces root competition but I cut most of the roots, except where currants are growing alongside the hedge. I plan to move the currants in a couple of year and will do some root cutting in the process.

    1. I have just returned from visiting gardening friends and they have just planted a rose border next to an old hedge. They have followed some very good advice by putting a two foot deep vertical plastic membrane at the base of the hedge to confine the pesky roots. Thanks for your comments Alain

  2. We don't top and tail our leeks and they grow just fine. It would upset me too to do it! In the last we have suffered from neighbours' leylandii but fortunately no longer. The only saving grace was that lots of birds roosted in the branches but we were still happy to see them go.

    1. Yes if used properly the Leyland can be a fine tree. A former colleague had a fine hedge but he did clip it umpteen times a year- six or seven times if I remember

  3. I wouldn't be without my trusty trenching spade for planting in woodland, I go as deep as I can rather than wide and put plenty of good material under the new plant which I hope is enough to establish it before the tree roots join in! It is also ideal for planting bulbs in areas a bulb planter won't touch.
    My first job was for a parks department and every winter we had to trench dig through the shrub borders chopping through any roots that got in the way. Never asked why perhaps I should have done!

    1. My first job also was in a Parks Dept. Rick. It was Hartlepool Parks and at they time our Parks Director was called Mr Grubb!
      Perhaps your trenching spade would jar my wrists less.
      I have never been fan of bulb planters and always use my spade!

    2. Just another thought Chris, One of my Parks colleagues was a superb craftsman.
      His digging over of the shrub borders was a joy to behold
      Pity it was such a waste of time!


Note: only a member of this blog may post a comment.

Related Posts Plugin for WordPress, Blogger...