On 26/05/2015 19:46, Chris Hogg wrote:
On Tue, 26 May 2015 18:32:52 +0100, stuart noble
wrote:

On 26/05/2015 16:02, Chris J Dixon wrote:
john west wrote:

Am trying to get into shape a garden containing some quite hard (but
seemingly good) top soil, but it has quite a lot of lumps of clay in it
(dug up from the clay bed from about a foot below) some time in the past.

I have some ready access to a endless supply of rotted leaf mold heaped
up from somewhere nearby and similarly a lot of old lawn grass cuttings.

With the intention of growing just flowers and shrubs (no veggies) in
the garden, should i try to remove all the lumps of clay ( a lot of them
are only a couple of cm across) ?

Whilst you are at it, gypsum is recommended as a soil improver
where clay is present, but appears to be sold in garden centres
as a proprietary product costing over £6 for 2.5 kg.

http://www.capitalgardens.co.uk/clay...er-p-6321.html

On the other hand, I picked up a 25 kg bag of multi-finish
plaster for under £5, and AFAIK this is essentially the same
material. It worked very well.

Chris


I don't think gypsum sets when mixed with water, but probably not
important in the long term

The setting action of plaster has nothing to do with it's action as a
clay-breaker. It's the calcium that does it, gypsum and plaster being
slightly soluble (~0.2% in water, IIRC). The calcium causes the
microscopic flat platy clay particles to clump together (flocculate)
in a more open structure (often described as an edge-to-face
house-of-cards structure, compared to the face-to-face pack-of-cards
structure it was before) which makes the bulk clay easier to manage.

Lime can be used to achieve the same result, but with an accompanying
increase in pH which may not be desirable.


Ah, interesting!