Re: Potting mixes
Janet Smithen wrote:
> The John Innis mix was never used in California. We, instead, made up a version
> of what was called the University of California mix. It was simply 2 parts
> organic mix to 1 Part inorganic mix. Different commercial companies made
> different versions.
Yse, this formula is known here, and is presumably the basis of a lot of
local commercial mixes but to me it has too many minuses, particularly
the intrinsic lack of fertility, (which means constant feeding) and
that dreadful tendency to dry out and then resist rewetting. I
occasionally buy plants in pots for my glasshouse and almost invariably
end up by repotting them to make them more user-friendly.
> I've grown up too, and no longer use peat moss and commercial products derived
> from sewerage sludge. Still use the 2 to 1 ratio; but now instead of sand, I've
> found a very coarse product at feed stores called granite grit (used for
> poultry). The compost part is hard if students don't make their own, they must
> buy something as close as they can. The ground wood can be any partly composted
> ground wood used for top mulching.
>
> Thanks to Moira, I've also gone to using kelp meal as an additive for trace and
> potassium. It's expensive here, boxed in its little 1 pound boxes, but I think
> it's worth it. I also add a fish-meal product available her, called Bio-Grow.
>> To this we added a product produced here called Gro-Power, at 2 Tbsp. to a
> 2-gal bucket.
I made a modified JI mix for some years, using unsterilized garden soil
and compost in place of sterilized loam and peat. The difficulty was
always what to substitute organically for their fertilizer mix of hoof
and horn meal, superphosphate and sulphate of potassium. For the two
latter one could use appropriate rock dusts, but the hoof and horn
defeated me. It has never been available in this country and their seems
to be no comparable nitrogen source which is sufficiently slow-release.
THe best I could come up with was a slow-release NPK fertilizer called
Magamp, which is actually a chemical COMPOUND of NPK with magnesium.
This comes in the form of irregular granules either fine or coarse. The
coarse sort are approximately pea size and are genuinely slow release,
surviving at least two years, so one can, I think, count them as a sort
of artificial mineral with which soil organisms seem to co-exist well.
Eventually I switched over to the compost/sand mix which was originally
described in OG some years ago as recommended by a NY organic research
lab, and I found that for small pots and short-term use the compost plus
kelp meal provided very adequate nutrition, especially if supplemented
with a couple of applications of a liquid fish fertilizer during each
growing season. The main advantage over my former mix seemed to be the
marked better health and growth of the plants, particularly in the great
reduction of soil pests and diseases. I used, for instance to have quite
a bit of trouble with soil mealybug, but haven't seen it for some time
and the other great gain has been in seedling health with no sign of any
damping-off problems.
For large long-term containers I tend to either top up with the sheep
pellets or for the more greedy things like camellias I do still use the
Magamp.
>
> Using a dollop of good garden soil (vegetable quality) for trees, shrubs and
> vines in large containers is wonderful advice. Thanks so much to both Moira in
> N.Z. and Glenn in S.A.
Glad to be useful.
And while I am at it, I will save a bit of time by a couple of short
comments on the other postings on this subject.
Deborah already has an answer on the composition of JI mixes, but she
also wanted to know what JI is and it stands for John Innis
Horticultural Institution, Merton England.
In 1939 they published the classic on the subject a little book of about
160 pages entitled "Seed and Potting Composts" by Lawrence and Newell. I
have a copy of the second (revised) edition which I bought in 1953 and
which was my potting soil bible for many years.
Whether this Institute still exists I have no idea, perhaps some English
correspondent could enlighten us.
And Dave, I don't like the sound of your chook poo preparation at all,
my sheep pellets are MUCH more refined and one has to put one's nose
close to the bag opening to smell anything at all (Though I must admit
to a slight farm odour in our hatchback car after having a bag for
several hours in the boot!)
Moira
Tony & Moira Ryan <theryans@xtra.co.nz>
Wainuiomata,
New Zealand (astride the "Ring of Fire" in the SW Pacific).
