Re: potting soil observation

Jan Smithen wrote:

In "Container Gardening" classes sooo many years ago, I found we had to make
our own potting mix because it was too expensive to buy for that many
people. I used the Univ. of Cal. 2 to 1 ratio: 2 organic to 1 inorganic
    1 part compost, 1 part washed coarse sand, 1 part ground up redwood
(called redwood soil amendment in those days) To that we added 2 Tbsp. kelp
meal OR 2 Tbsp. Gro-Power for every 2 gal. bucket of mix. Depended on what I
could find in those days.

Lots of work, mixing and blending, but it worked very well and taught me the
value of grit in a soil mix.

Jan
This is very similar to the mix I use, though I got my recipe from some NY lab which was quoted in Organic Gardening in the days when it was still a useful publication. Mine however uses just compost for its organic portion. With my own compost this seems substantial enough for small containers and for large pots I do add some soil as well. I am sure I could get ground bark here quite easily, as pine bark is the medium of choice for many commercial mixes and I might try your recipe some time. My experience with mixes using bark only for their organic fraction is definitely not favourable though, as on its own it tends to be a bit like peat - once it has dried out it is extremely difficult to rewet and watering consequently almost always involves regular soaking of the pot. In any case such mixes, unlike those with compost have very little intrinsic food value and usually depend on regular additions of chemical fertilizers to sustain the plants.

I find my compost-only plus kelp meal mix is very adequate for the majority of plants in my greenhouse for at least one growing season. For some of the larger and more permanent plants though I do add a substance called Magamp which is easily obtained here. It comes in the form of irregular granules and is in effect an artificial rock containing NPK and Magnesium chemically combined in a form which allows only slow release and so is not a danger to living organisms, which can draw on it as required. It can be used in open ground also, where its effects last easily up to two years for one application. In my business days I used it very effectively for establishing new roses for instance..

For my grit fraction I use a half and half mix of propagating sand and coarsely ground pumice (both freely available from my favourite garden centre). I am interested to hear though of someone else using just grit and not Vermiculite or perlite, both of which are both hard to get here and expensive when one does.

I found the easiest way to do the mixing was to spread the ingredients out on large piece of plastic sheet. Quite a lot of the stirring can then be done simply through rolling the heap over trough lifting the sides of the plastic.

--
Tony & Moira Ryan,
Wainuiomata, North Island, NZ.     Pictures of our garden at:-
http://mywebpages.comcast.net/cherie1/Garden/TonyandMoira/index.htm
NEW PICTURES ADDED 4/Feb/2004

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