| Soil Test Kit for
NPK and pH
How can one decide
what type of compost is most suitable for a particular plant. Fortunately
the days have gone when some 'experts' advocated a special compost for
Two approaches are outlined below. The first one is an amalgam of Branch
committee members' views on composts for both cacti and succulents. The
second is based on some elementary botanical reasoning which may also
Almost all committee members base their composts on about 50% John Innes
(JI) No 2 or 3. The other 50% is made up by chicken grit, small stones,
or perlite, although one member said it sometimes looked like mealy bugs!
None added any fertilisers because there is enough in the JI mixes. Fertilising
is almost all done on roughly alternate waterings with Chempak plus occasional
shots of normal fertilisers like Phostrogen and Baby Bio, especially at
the beginning of growth. None use peat, but advise being careful about
the content of JI because not all manufacturers follow the correct formulae.
That formulation is given in the Appendix, John
The committee also urge caution in what is added as grit; be careful it
is not crushed shells or other lime-rich stones. It may also be helpful
to check the pH of your compost because the acidity of peat can vary.
Another important consideration in any compost is the need for trace elements.
It is not enough to see 'contains trace elements'; the actual elements
should be named. Sometimes called 'micronutrients', one would expect boron(Bo),
copper(Cu), iron(Fe), manganese(Mn), molydenum(Mb), zinc(Zn), to be actually
specified because they help in a plants uptake of certain nutrients.
'Doing Your Own'
If you want to make up you own compost there are various alternatives.
A loam or 'top soil' would comprise about 50% of it. An old gardeners'
trick was to use soil from mole-hills. The reasoning being that it came
from some depth down, not from the surface where all kind of things dwell.
Then add a good portion of sand or gravel, and finally some (about 10-15%)
of sphagnum peat. The critical gardener might then want to test the mixture
for N, P and K with the kind of kit market gardeners sometimes use. These
kits look similar to pH test kits. A good general fertiliser is 'Growmore'
introduced during the last war, and still as good as any today. Alternately,
a mix of bone meal, blood & fish, etc will be adequate to start with.
It might be worth while testing pH. It is usually easier to make a soil
more alkaline than more acid. If acid then hydrated lime would make it
more alkaline. On a loamy garden soil 8oz (250g) of hydrated lime per
square yard, would raise the pH by 1.0 point. If alkaline then sulphur,
even some peat, would adjust that.
The second approach, referred to above, begins with a botanists' rule
of thumb. The rule seems to be that wet areas are acid because there is
more vegetation producing acids by respiration, decay, and excretion.
Dry areas, on the other hand, have less vegetation and these processes
do not occur because of less rainfall. There is then less washing out
of substances which cause soil alkalinity to increase.
Following on from that it might be said that plant evolution has favoured
mutations which enable dry area plants to cope with alkaline soils and
wet area plants to cope with acid soils. Cacti and succulents seem to
be nearly neutral (pH of 5.5-6.5) and not as sensitive as azaleas, camellias,
and rhododendrons, for example, which need a pH of between 4.5-5.5 But
another school of thought suggests that some of the more recently evolved
cacti, such as mammillariae and its close relatives, might like something
on the other side of neutral. pH values are not as close as one might
think. See 'What is pH' in the Appendix for more details.