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Clay soil & gypsum


apologies if this has been covered before or if it’s a stupid question, but I have a part shade garden which was re turfed last year, and although I wasn’t happy with the final outcome I have to deal with what I’ve got. Apparently at least half of the garden is on a bed of clay, a common problem in my area I’ve been told....looking into it, all I’ve come up with is putting down gypsum to break the clay up and let the grass, earth breathe. Is this right? Has anyone had any experience with this? I just don’t want to be digging up the garden ideally. 

Thank’s in advance. :-) 


  • pbffpbff Posts: 433
    edited March 2018
    Hi @Neil.lyon,

    Welcome to the forum!

    "There are naive questions, tedious questions, ill-phrased questions, questions put after inadequate self-criticism. But every question is a cry to understand the world. There is no such thing as a dumb question".
    Carl Sagan

    Having a clay soil is not necessarily a problem, provided you know how and how not to care for it.
    Clay soils are in fact packed with nutrients and retain nutrients and water very well, which is great.
    The problems with clay occur when it is excessively wet.
    Clay drains very slowly and if the ground is worked or trodden on when it is wet, it becomes compacted, destroying the structure of the soil and making it even more waterlogged.
    So rule no.1 of gardening on clay soil is never walk on or work the soil when it is wet!
    Constructing proper paths or placing stepping stones in the lawn is a must, as high traffic areas will quickly be ruined by walking on them.

    Digging can do more harm than good on a clay soil; you have a very narrow cultivation window usually between autumn and early winter in which any digging can be carried out. Throughout the winter and early spring it will be too wet. In the summer, as the clay dries out, it will become hard and often shrinks and cracks and cannot be worked then either.
    Employing the no-dig method is much better. I just mulch with plenty of well-rotted bulky organic matter and let the worms incorporate it (you get less weeds with the no-dig method too!)
    Bulky organic matter (i.e. garden compost, composted bark, spent mushroom compost, well-rotted farmyard manure) is great for improving the structure of a clay soil. 
    All soils contain three sizes of pores: macro-pores, meso-pores and micro-pores.
    When the soil is made up of larger particles, there is a higher percentage of macro-pores, which don't hold water for long e.g. in sandy soils.
    When the soil is made up of tiny particles, there is a higher percentage of micro-pores, which are permanently water-filled (however this water is mostly unavailable for plant uptake due to it being held hygroscopically) e.g. in clay soils.
    By adding bulky organic matter you are increasing the amount of macro-pores within the soil, thus reducing problems with waterlogging and compaction.

    Gypsum helps to bind the tiny clay particles together to form larger ones (a process called flocculation), but it doesn't really stabilise the soil structure in the same way that bulky organic matter does.
    It doesn't always work on all clay soils either.
    It always worth testing on an area of soil in your garden before you buy a whole load in to see whether it works on your soil or not.

    I'd personally go for the addition of organic matter first and sort out some sort of path for your lawn, rather than the gypsum.

    I hope this is of some help.

    All the best.
    pbff  :)
  • Pbff,

    thank you you for getting back to me, wow a very comprehensive response! :-) 

    i will give that a go with the bulky organic matter then. I was advised by the gardener who was paid to lay the lawn that it would need digging up, as the local area is known for its clay base....(a point he neglected to mention when quoating the job!) and to put top soil down with some grass seed. 🙄

    with thanks.

  • pbffpbff Posts: 433
    edited March 2018
    Sounds like said gardener was hoping for two jobs out of you then!
    It is common practice when laying turf on clay soil to lay the turf on a bed of sharp sand first. It isn't necessary to grow a lawn from seed on clay.
    I hope I didn't bore you too much with my post - I am prone to waffle on a bit about soil!
    All the best.

  • No not at all! I was going to offer you a job! ;-) 

    im just hoping it will break down the clay enough for new grass seed to grow. Do you recommend aerating the lawn first too I take it? It has been like a bog with all the recent rain.

    best wishes.
  • pbffpbff Posts: 433
    Ha, ha Neil!  :D
    Don't do anything to your lawn at the moment while it is still wet.
    Once it dries a little, then you can look at improving it.
    You won't be able to get much in the way of bulky organic matter into an existing lawn, although it is a good idea to add it to beds/borders.
    You can slit/spike the lawn and lightly top-dress with organic matter and sharp sand, which may help eventually.
    Much of my garden consists of beds and borders, with relatively little lawn - so I'm not as experienced in managing lawns on clay soils as I am beds/borders.
    Just been hunting about on the Forum for a thread on the subject and found this one:

  • Pbff, we have only been in the house 2 years and with the arrival of our first child I wanted to get the garden sorted....looks like plan B and put an extension on the back lol thanks for the advice though and I will try your suggestions in the mean time.

    all the very best.

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