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Re: customizing soil for container vegie gardening (fwd)

Margaret M Daniels wrote:

> In various books I have seen it hinted at that one can create different
> soil mixtures to suit the preferences of the different vegetables,but I've
> never seen this laid out in detail (they then give an "all-purpose" mix,
> which spoils the fun!). I like to experiment, so the idea of
> doing this appeals to me.

I've only ever done this in connection with container growing - but perhaps
raised squarefoot beds count as large containers. Most instructions and
greenhouse practice use sterile, processed materials ordered in bags or bales.
Here is a list of soil amendments and their purported properties:

1. Compost - screened and sterilized. The nutritive component of the soil mix.
May also have other beneficial effects on plant growth.
2. Sand - not sea sand, sharp quarry sand like that used in concrete. Added to
improve drainage.
3. Peat Moss - a sterile and not very nutritious medium, whose humus texture
is said to encourage root growth. Used to add a friable, fibrous texture and
aid water retention. Available in coarse or sieved textures. The sieved
product makes up the bulk of most seed-starting mixes.
3. Vermiculite and Perlite - both are heat-expanded rock - perlite even looks
like mineral pop-corn, which is just what it is. Vermiculite is a gritty
popped quartz, and while improving drainage of heavy soils, still retains
moisture: it is used in some hydroponic schemes to give roots something to
cling to. Perlite is a lightweight aggregate used to improve drainage.
Unfortunately, many greenhouses now use styrofoam instead of perlite, since
the two are identical.
4. Cocoa fiber - chopped/ground coconut shells, including the fibrous husk,
compressed into a brick. The brick expands when moistened. The combination of
gritty shell bits and shredded fibers offers texture and drainage. HOWEVER
every time I have used this product - both in Israel and the USA - I was
warned to thoroughly soak and rinse the fiber, since it contains sea salt from
processing.

I have never heard of anyone selling heavy clay soil in bags, since the goal
in most potting mixes is usually a light, friable mix. But if you have such
soil, it may be useful in small amounts, to bind the fibrous elements and
increase water retention and nutrition.

The other big reason why people prepare soil mixes is to accommodate pH
requirements - and I feel this is more crucial than soil texture in most
cases. A relatively fertile, friable soil that is sufficiently deep and kept
sufficiently moist should be able to grow many things. But pH can be a real
limiting factor: acid loving plants will turn yellow due to chlorosis
(inability to extract iron and manganese from alkaline soil). Lime-loving
plants also suffer in acid soils. Here is where "laboratory formulated" soil
comes in.

Peat is known for its moderate, long-term acid reaction, and is therefore used
to acidify soil. Often large amounts of compost are added to alkaline soil to
moderate its effects. Compost of pine trees is particularly good at acidifying
soil.

Dolomitic lime powder is added to commercial seed-starting mixes to
counterract the acidity of the peat. Other than than, most of the amendments I
have listed are pretty neutral in their pH reaction.

Ben


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