Subject: Re: clay soil + compost = adobe ???

From: [email-masked] (S. Plunkett)
Date: Thu, 9 Mar 1995 12:22:36 GMT

Anthony Brewster ([email-masked]) wrote:
> I recently added 1 part compost/mulch to 8 parts low organic clay soil. A week
> after thoroughly mixing the soil + a little gypsum, 2-3 inches of rain fell
> and turned the soil into a thick paste which lost a lot of volume and is
> now drying into a hard adobe like mass. In a sense, the soil now seems
> more compacted than before the organic material was added and is going to
> need a lot of fluffing up to be suitable for planting.

You will probably have to add quite a bit more organic material to
soften up your clay.  Adding some fine sand will also help to make it
more suitable for gardening.

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From: [email-masked] (Lena Bolander)
Date: 9 Mar 1995 08:11:36 GMT

In article [email-masked], [email-masked] (Anthony Brewster) writes:
> The question I have is did I not add enough compost(Nurseryman's brand, forest
> products), or are some materials better than others at loosening up clay soils?
> Also, does the loosening effect take time to happen, ie does the organic
> matter have to decompose some before it really has an effect? How many more
> parts of organic matter should be added, if any? BTW, I also turned over a
> cover crop of rapeseed, rye and hairy vetch, and added about 0.5 parts kitchen
> scraps.
> 
> Thanks..Anthony
> 
> 
> 
In order to change the soil structure you have to ad lots of the new material
(compost, mulch, sand or whatever soil you want) to the surface, as deep as
 you need for your crop roots. I dont know how much of compost it takes but for
changing clay-soil to light sandy soil there has to be more sand than clay in
the blended result. 
But your clay will be fine as it is though it need some "fluffing" now. If you use
grassclippings or other fresh green material to cover the soil between the plants
the worms will do the fluffing for you during the growing season. Cover should be 
about 5 cm thick. Clay holds water quite well and the top cover added to that will
 keep the soil moist much longer than if you had a bare soil. It does also prevent
 the clay from cracking and getting hard. If you continue to use this method your soil
will improve a little for each season by containing more organic material.
You have also to choose a crop that is suitable for the clay. I have had some
difficulties with carrots earlier but now the grow much better though they not
are perfect (yet).

regards

/Lena

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From: [email-masked] (nightjar)
Date: 13 Mar 1995 22:01:50 GMT

>cover crop of rapeseed, rye and hairy vetch, and added about 0.5 parts kitchen

Adding organic matter is not always the answer. On poorly drained soils it actually
decreases fertility - turning the soil anaerobic and sour. The way to check drainage
is to dig a hole about 2 feet deep when the soil is moist. Fill the hole with water and
if most of it is still there next day you should think seriously about sub-soil drains.

If you have used un-composted organics, they will need to decompose before they
have the best effect. You will also need to add Nitrogen fertiliser while they are doing
so as they absorb Nitrogen while rotting. Well composted organic material, although 
dearer, has an immediate effect.

In the UK clay soils respond best to digging over in Autumn and letting the frost
get at them. I somehow doubt that is much use in L.A.

Unless you want to grow lime-hating plants, the next best thing is to put on lots
of lime. This causes the soil to flocculate, i.e. stick together in small clusters, rather
than large clods, so it becomes more manageable. Alginates, from seaweed can
have the same effect.

The ultimate solution for clay soil is to add an equal quantity of sharp sand and mix
well. Unfortunately, except for the smallest gardens, this is not often a practical
method. The ideal soil is about 50% sand, 25% silt, 20% clay and 5% organics.

Happy digging

Colin Bignell

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From: [email-masked] (Lena Bolander)
Date: 14 Mar 1995 07:50:10 GMT

> if most of it is still there next day you should think seriously about sub-soil drains.

As Colin says the draining might be bad. This quite common with heavy clay which
have been packed by use of heavy machines on top of it. When plowing only the top
layer gets turned. The layer beneath is getting harder and harder. This is also
way rototilliers not are very good to use on heavy clay. 
In order to correct this you need deep digging. Of course there may also be bad
drainage which need to be corrected sub-soil drains but there may also be just 
enough with som digging.
In order not to pack the clay  you might make beds which you reach over without
stepping on them an which you keep at the same place from year to year. Then you
do not need the heavy work of digging each autumn.
I use this method myself together with covering the soil with grassclippings during
the growing season.

/Lena