Supersoil
totototo@telus.net (Mon, 24 Nov 2008 14:34:43 PST)
Interesting to read about the decline and fall of Supersoil.
Some very green-thumbed growers here use commercial Sunshine Mix, peat
based, but I prefer to mix my own starting with "Island's Finest Top Soil."
This raw material is fairly cheap, typically $2 or $3 for a 30-liter bag. It
appears to be excavated from an old lake bed, so it's a natural mixture of
peaty materials and silt. Heretofore, there's always been enough rough
twiggage in it to demand that it be screened before use, but this year no
such problem.
My target is a mix that is close to the famous John Innes potting compost
without getting involved in the arcane intricacies of Cornish silver sand,
stacked turves, and hoof-and-horn meal.
Here's the exact recipe I use these days:
30 liters of soil
16 liters of horticultural perlite
150 g of organic 4-6-8 vegetable fertilizer
170 g of lime
7 g of fritted trace elements
Notes:
1. If the perlite bag doesn't say "horticultural", it may contain soluble
fluorides. These won't cause a problem if you are pouring the stuff into the
wall cavities of your house as insulation, but your plants will take
considerable exception. My original recipe (which I may have posted here
before) only called for 6 liters of perlite, but I found the result was somewhat
too peaty and airless for comfort. The increased quantity is simply based on
"how the stuff feels" when you rub it between the palms of your hands.
2. I use an organic fertilizer in the belief that it will break down more slowly
than a fertilizer compounded primarily from soluble salts.
3. Lime. I use ground limestone or agricultural lime, not dolomite. The
purpose of the lime is to bring the pH of the finished product up to about 6.5;
dolomite is too insoluble to do this. I recommend to those who also mix their
own soils that they buy some pH testing paper and use it to verify the pH of
their final product. The lake bed material I start with has a pH around 4, very
acid, so requires a surprising amount of lime to bring it up to near neutrality.
4. Fritted trace elements. This takes care of any trace element deficiencies
but is little enough it won't overdo any of them.
--
Rodger Whitlock
Victoria, British Columbia, Canada
Maritime Zone 8, a cool Mediterranean climate
on beautiful Vancouver Island