Ealdwood welcome to the complex world of non-traditional potting mix for growing cacti & succulents in containers. There are alot of lot of information available in this forum regarding the vast array of different soil ingredients/components you can use, along with its attributes and benefits to porosity, water retention and aeration.
So far, I have only have tried the popular 1-1-1 gritty mix (GM) and a coarse bonsai mix (75% inorganic/25% organic soil), it's basically like your gritty mix, but was added with volcanic rocks. After encountering fungus gnats, spring tails, the death of a few plants (through rot) and a couple of excruciatingly warm summer weeks, I'm relooking into tweaking my mix (since I finished using my batch of GM as well) and watering habit to match the humidity level and temperature.
A few forum members swears by perlite, pumice and volcanic rocks as a core ingredient in their modified mixes, but so far I'm taking one step at a time and am experimenting with perlite to increase porosity in my GM.,
Trust me, you will hear ALOT of recommendations, but what works for someone growing haworthia outdoors in North Cali, might not be ideal for someone like me who leaves in the East, growing mostly Echeveria succulents indoors. So reading into recommendations are great to learn, but at the end of the day you need to find something that works best for you.
For starters, the 1-1-1 GM is good enough and works as a good standard mix for most Cacti & Succulents (key word, most, not all), until you start adopting the more "fussier" plants, you will need to do more research and reading, which is what I'm doing now.
There are a few varying factor that will require you to analyze before choosing what works best for you.
1) Knowing your C&S plant! The key is identifying them and knowing the type of roots they have, this will greatly help you to meet their needs, as some prefer more air - which means you need to have more porous ingredients or have the ingredients sift at a larger size.
Take for example, Haworthias, are monocots type plants with thick fibrous fleshy roots. These plants enjoy long deep pots with a medium that holds moisture better and a more coarser size (say about 1/8") to encourage their tap roots to thrive. More Excerpt as described by Mark/Xeno below:
"Haworthia have a long and extensive system of fleshy roots. If they are crammed into a small pot, which is likely because that's how most succulents are grown, they will be prone to damage.
The fleshy roots are best in a medium that does not dry out completely. Those thick roots need a consistent moisture level which may not be easy to accomplish especially in a cramped pot where there are greater temperature fluctuations. Remember that roots in a pot are not at all like roots in the ground - the substrate is much less stable in a pot. Roots easily get too hot or too cold, and will often just die back without you realizing.
Since these are monocots, roots are regenerated from an initiation zone at the base of the plant. This takes longer than dicots which can root more easily, in general.
I would bet the roots were gone or on their way to being gone earlier this spring, you're just seeing it now. I know this from experience. Put the plant into a new substrate without any peat, something gritty with perlite, turface, etc. Place it in a shady spot and wait. New growth probably won't come until nights are cooler in September. The temp variation outdoors is MUCH healthier than growing the plant indoors at room temp. Indoors is good for tropical plants, not so good for subtropical stuff like many succulents."
Source
I believe most regular succulents such as the Crassulaceae, echeveria family enjoy shallow pots because they encourage extensive root hairs to reach outwards horizontally instead of vertically, and shallow pots allows the mix to dry faster.
2) Choosing the right pot.
Too big, too small? Clay, plastic? Glazed, unglazed? Deep, Shallow? - Can all work differently even if you use the same soil mix for all.
Initially I started out with those cheaper plastic pots, just because they were much easier to attain and are cheaper because they came with the plants when bought. But now, almost all of my plants are in terra cotta pots because they allow good air circulation to reach the soil and roots much faster.
You have to know when growing plants, especially succulents in pots are very different from growing them in the ground. Our job is to mimic the environment as close as we can possible by meeting those conditions and it's usually tougher to master this balance.
Plants grown in the ground have their roots kept deep enough underground without constriction or limits, so temperature on the surface wouldn't greatly affect the plant's roots health. Imply that similar concept and put the same roots grown in a small 6" pot, the soil has no natural protection or have any cooling/heating agent from heat or cold. Too hot - they desiccate and fry, too cold they freeze and die too.
It's always when the roots die unsuspectingly (simply because it's hidden from the eye and usually do not show signs of stress on the foliage), we continue to water them without knowing until it's too late, and the stems/roots rot and eventually die because the plant has no more roots to take in the water we give, and sitting water, dampness = death.
3) Watering Habits
Some people grow succulents mostly for their drought tolerance potential, and have little to no time to water their plants. These people will often benefit from a more water retentive base mix, though theoretically it isn't great for the plants in the long run, but it's what works best for you matters in the end. Some people (like me), have personalities to be overbearing to their plants needs in terms of watering. To me watering sessions are the only opportunity for me to interact and inspect my plant's health, so I do it every few days to weeks during the summer, weeks to months during winter/spring.
You'll be surprised that some people on this forum face quite some problems with the GM and are in fact switching back to 50-50 perlite-peat. I believe my mix needs to be more porous than the regular GM version to match my watering habits. The reason why some members are recommending the completely inorganic route, is because organic materials decomposes, and those product creates bacteria, acting as hosts for fungus and attract pests to your plants, ultimately threats to the roots.
If you notice, the fundamental core of healthy plants all revolves around healthy roots, and this is why it is so hard to master, because it's all about creating a balance of all of the above, as well as matching your growing abilities.
I'm sorry if I didn't answer your questions directly, because at the end of the day, you have to decide what's works best for you and your plants. We only can offer what we have learnt and know from experience.
I found these articles through research, and they have been profoundly helpful for me, in terms of listing the different types of soil substrate available along with their effects/benefits, and I hope they'll do the same for you too.
http://forums.gardenweb.com/discussions/1834859/informative-reading-about-soil-mixes
http://www.labs.agilent.com/botany/cacti_etc/html/soils.html
http://forums.gardenweb.com/discussions/1853340/soil-substrate-comparisons
Purposes of soil:
The soil mix provides physical support for the plant, acts as a source or
reservoir of water and nutrients, allows circulation of air to the roots
while protecting them from sun damage and desiccation. For some species
it is also important that the soil serve as thermal storage allowing the
plant to survive greater temperature extremes than it could in bare-root
form.
Natural Soil Components:
Most cacti and succulents live in soil with perhaps 3% to 5% organics.
The remainder is mineral and may include particle sizes from clay up to
boulders. Finer soils allow less air circulation and tolerate much less
water before risking root suffocation and rot. Conversely, coarser soils
require more frequent watering to avoid root death due to desiccation.
Desert soils do not experience the cultivation that worms perform in
temperate regions. Neither do they develop thick layers of humus from
which minerals and humic acids leach with each rain. Rapid surface drying
slows the breakdown of plant residues. In the Sonoran desert, carpenter
ants may be the major force for removal of surface residues. In Africa,
it is the termite. The major source of soil organics does not come from
above. It is the roots of prior plant generations.
Except for plants with seeds that must be deposited by flowing water like
the river paloverde, plants do not choose their soil. They try to survive
where they are. The soil in which they naturally survive may not be
optimal and may just be too poor to support any competitors. Not
surprisingly, there are perfect soils in which practically any plant will
do well. Such soils are so rare in nature that no species would evolve to
depend on them and no collector would perceive them as the native soil
for any particular species. Nonetheless, we can produce such soils
artificially.
Available Natural Components:
Clay particles array themselves in a fashion that stores water and
nutrients and in natural soils prevents both from sinking below the root
zone. They also pack so tightly that root aeration is compromised. As
much as 10% clay in the form of kitty litter may save mixes that would
have been too friable to hold plants upright. Clay makes the mix stick
together but must be used in moderation.
Fine sand/silt in natural soil holds moisture in narrow interparticle
spaces and wicks moisture into the root zone from the subsoil. This
service is not needed for potted plants. The particles pack too tight for
good root aeration and offer little ion exchange capability. They also do
little to support plants structurally. There is no specific need for sand
in a soil mix.
Natural gravels and pebbles improve air circulation but do not hold water
or nutrients. They are often so rounded that plants potted in pure gravel
just tip themselves out of the pot. Sometimes a little clay will hold the
mix together but pebbles are best used as a top or bottom dressing or as
the starter medium for aero-hydroponic systems.
Those who want to screen their own should discard particles under 1 mm
which would pass through the typical kitchen strainer. The 2mm to 5mm
particles which pass through 1/4" hardware cloth are useful for soil
mixes. The 5mm to 10mm pebbles which pass through 1/2' hardware cloth are
best for hydroponic use or as top dressing for large plants.
Granular diatomaceous earth looks like kitty litter and has particle
sizes from 1mm to 4 mm. It absorbs water in its pores and supports ion
exchange. It is sold as a mechanic's oil absorbent and would be a perfect
medium if it were available in coarser form. It is a great top-dressing
because it does not stick together and the surface quickly dries to
eggshell color. Even without much cohesion, its weight and wet-ability
provide good plant support.
Crushed pumice shares the same characteristics and is available in
coarser sizes. It is not cheaply available in most areas in less than
boxcar-sized loads but is the product of choice when available.
Crushed basaltic lava rock has larger vesicles and lower silica content.
The particles cut into each other providing better physical plant support
than any other medium. Lava rock is slightly soluble. Minerals leach out
making the soil more alkaline and it breaks down into smaller particles
over time. A high proportion of lava rock will cause the same problems as
will sand after enough leaching.
Peat moss is the decomposed remains of temperate bog mosses. Its fine
particle size requires moderation to avoid root suffocation. It releases
humic acids which may combat some root pathogens but in breaking down it
competes with the roots for available oxygen. As a primary component it
resists re-wetting after drying but in proportions less than 25% and when
ground with the other components through 1/4" hardware cloth re-wetting
is not a problem.
Peat moss stores water and nutrients well while providing little of its
own. It helps in physical support by holding the soil together but relies
on fine roots and fungi to assist in that task.
Peat moss is a thermal insulator and prevents plants from transferring
heat to or from the soil. Plants potted in peat moss will have lower heat
and cold resistance.
Peat moss lowers the PH of soil and is useful to compensate for lava
rock. Otherwise, one to three tablespoons of lime must be added per cubic
foot of peat moss to avoid excess acidity. Dolomitic lime is preferred to
avoid an excess of calcium compared to magnesium. Peat moss is mined from
environmentally sensitive areas with limited regenerative capacity. Many
avoid it for that reason and use the alternatives described below.
Artificial Soil Components:
Vermiculite is an expanded form of mica. It holds water and minerals well
between its layers. It tends to shrink when wet and expand when dry and
moves a lot when watered. The volume changes can be compensated by about
one gram of polyacrylamide crystals per liter. As with lava rock, the
particles break down over time. Since the surface of vermiculite dries
too fast for exposed seedlings while the depths offer too little air
circulation for most plants, it should be used sparingly, no more than
25% of the mix.
Rock wool is derived from a mixture of ground stone which is melted, spun
and compacted. It holds water and minerals well but slowly releases
alkali like lava rock. Its fine pore size may suffocate roots except
where the smallest cubes of rock-wool are used for seedlings. In
hydroponic use, larger plants are allowed to arrange their roots on the
surface of a rock-wool slab while plant support is provided from above.
Bulk rock wool looks like grey cotton and can be used in soil mixes. The
chunks do tend to stick together and aggregate. Breaking them down
through a 1/4" mesh screen embeds a multitude of fine fibers in one's
skin. There are many better alternatives to rock-wool in a mix.
Perlite is an expanded silica. It is slightly porous, offering some water
and mineral storage capacity. It provides good plant support when wet or
dry but tends to suspend itself during watering. It will let a plant fall
over but will stiffen up when the water drains out. It will also float up
through a top-dressing. The main value of perlite is its support for air
circulation while also distributing water well through surface wicking.
Many plants grow well in straight perlite with hydroponic feeding. A pot
or tub of perlite can water itself via a fiber wick extending into a
vessel of hydroponic solution. Perlite is an excellent bottom dressing to
prevent potted plants from wicking up too much moisture from drainage
saucers. Some sources of perlite have high alkali content, mostly
potassium and will raise soil PH over time.
There is also a styrofoam product called styromull with characteristics
similar to perlite. Some European experts recommend it but it does not
appear to be available in the Americas.
The three products described above are thermal insulators having the same
limitation described for peat moss.
Baked clay spheres or extrusions which are collectively called grow-rocks
in the hydroponic trade provide drainage and air circulation and store
significant amounts of moisture and minerals. They are too coarse to use
in other than hydroponic systems and most are too smooth to provide good
plant support. A variant made of expanded shale avoids those limitations
and is the equal to pumice. These products are of little value in low
concentrations, becoming expensive pebbles and are too expensive to use
in quantity unless one has a local manufacturer. As with the natural
mineral products, shipping costs far exceed the initial cost of the
material.
As an alternative to peat moss, one can use mixed compost or composted
bark chips. Mixed compost may contain manure, fallen leaves, grass
clippings, agricultural residue, recycled newspaper and/or sawmill
residue. Most are well composted and can be used like peat moss but
without the re-wetting problem.
One superior product called "America's Choice" was long-fiber sawmill
residue. The long fibers provided plant support but were coarse enough to
avoid packing down and suffocating roots. Alas, Wal-Mart no longer offers
it. Perhaps some of the list members can find alternate sources.
Bark chips have a much lower surface to volume ratio. They offer good
drainage and can be used in high concentrations without suffocating
roots. They do not offer good support and slide over each other easily
but are much less likely to float up than perlite. Eastern sources of
bark have predominantly 1cm and larger particle sizes while western
sources are below 1 cm. One can screen it and use the same particle sizes
as were recommended for gravel. Bark is not fully composted. It releases
humic acids slowly so that little lime is needed to regulate PH but it
can absorb significant amounts of nitrogen from the soil mix during its
initial breakdown. One can add a tablespoon of dolomite per cubic foot
and 2% to 3% by dry weight of nitrogen in some soluble form to a dampened
mix and let it re-compost a few weeks before use.
Favorite Mixes (FLAME BAIT):
My favorite mix for aero-hydroponic use is equal parts of pea gravel and
bark chips which will pass through 1/2" hardware cloth but not 1/4"
hardware cloth.
My current favorite mix for daily watering with hydroponic solution is
equal parts of granular diatomaceous earth, perlite and screened bark
chips. All pass through 1/4" hardware cloth but not through a 1mm screen.
My favorite mix for gift plants which will be watered irregularly with
our local alkaline water contains equal parts of peat moss, vermiculite,
perlite and granular diatomaceous earth with 1/2 tsp of polyacrylamide
crystals, one tablespoon of Osmocote pellets and two tablespoons of bone
meal per gallon of mix. The mix goes through 1/4" hardware cloth just to
break up the lumps.
The
Future:
Please post your opinions if you disagree with any of the above. Describe
any products that you use which are not included. Also post your favorite
mixes which will be used to adjust the recommended ranges for ingredients
and combined into a recommendation which allows for locally available
alternative ingredients.
Happy Growing,
Bernard
Q