Soil Mixtures Pros and Cons

Soil mixtures pros and cons

Our basic soil mix is exactly the same for every single plant species we grow.
There are many reasons for this.

The main one is that it worked consistently best for the widest range of species in our very extensive side by side trials.
I germinated and grew 100’s of different species in a couple of dozen different commercial mixes as well as half a dozen that I mixed up myself based on what others had suggested to me.
I have since repeated this test more than a couple of times over the years as my supply of materials unfortunately changed.
In each of these side by side trials, the various soil mixes were always watered three very different ways.

My trials were also always designed to kill a huge number of plants to really get to the bottom of what Darwin reckons is best.
Without lots of failure and death, it’s a pretty pointless exercise.

  1. The first group was flooding, and to do that the trays were lined with plastic garbage bags.
    Cheap, reusable and they fit a tray of 20x 100mm pots perfectly.
    This meant the pots were constantly sitting in water and every time it dried out they were just re-watered again.
    This causes a huge amount of death by root rot and damping off as the soil doesn’t drain well.
    When we first came here major flooding rains were an issue and this is an extreme simulation of those conditions.
  2. Drought was the second group, and for here it’s the most common weather pattern over the last half dozen years.
    These ones were only watered each time there were losses from dehydration.
    If they got the rain that was lucky for them, but if it didn’t rain I just waited until most of the species of plants were wilted and a small % had actually completely died.
    I then only watered them enough to prevent immediate death to the remaining majority.
  3. Control. This is the most important group as without it your results mean bugger all.
    People are always saying “I always do X and it works great, far better than when I use to do Y instead”.
    My response to that is how the hell can you form ANY opinion if you have only done one single thing, at one single point in time.

Side-by-side trials are NEEDED if you ever really want to know if something works best or not.
To do that you need a control that gets no special or unusual treatment.
These guys in the control group just got looked after and watered when they needed it.
Even with that high level of TLC and near-perfect conditions many of the fancy commercial mixes performed dismally.

Soils mixes that contain a lot of water crystals, silica beads, peat, coco peat, chipped palm, or highly absorbent insoluble fibre all hold water really well which is handy in normal-good conditions. I have no interest in good conditions as any doofus can keep a plant alive then…

My focus is always on the extremes and how to prevent dramas in less than ideal conditions.
If you invest your time in preparation and get that bit right then they not only survive the hard times that always inevitably come, they absolutely pump during the good times!

Unfortunately when waterlogged this highly absorbent stuff actively kills your plants by lowering the oxygen levels in the soil damaging the roots. It swells and expands forcing out all the air spaces and this causes cell death and rot. This then causes even more stagnation of the water, and in these water-logged soil conditions, anaerobic bacteria completely proliferate.
These bacteria and their waste products are acidic and they even further corrode,  burn and damage the roots, while at the same killing and feeding off all the good bacteria and fungi that healthy soils really need.
It’s all bad news, unfortunately.

When the soil eventually dries out again the normal air spaces that were in the soil have collapsed.
Even if the plant initially survived it is now trapped tightly in a shrunken solid brick of fibres that strangle and choke the delicate and now very damaged roots.

This shrunken paper mache looking lump can no longer absorb water and all the rainfall or water you pour on the plant just runs to the edges of your pots and straight out the bottom.
Failing that in really big pots or raised beds it runs along the large cracks in the surface of the soil, straight past the plant roots, and immediately deep into the soil when the plant can’t actually access it.
It provides the plant with no benefits at all, and the affected plant inevitably dies. The more expensive and fancy the potting mix, the more often this issue happens.

“Hydrophobic soil” like this will eventually kill a plant by dehydration, despite the issue actually being caused by too much initial water retention.

Sand is great stuff as it’s generally high in minerals and trace elements, and because of the very large surface area, it gives heaps of room for bacteria and fungi to set up shop. If you look at sand under a microscope it’s like a rough diamond, with heaps of flat bits. Pretend each grain of sand is actually a cardboard box.
If you unfolded the box and lay it out flat it’s huge!
If you pretend a wood chip or a composted plant fibre was a cardboard box roughly the same size it’s basically just a stretched and twisted shoe box.
It only has a few sides so when unfolded and laid out flat it is nowhere near as big in surface area as a piece of sand of the same size.

The very large surface area that sand provides gives homes for all the good guys, and as well as that it leaves air spaces that roots need to thrive. Air is just as important as water, it really truly is!

Soils that are too high in sand and are too free-draining are not great either, but there are no mixes commercially sold that have this issue. The reason why is weight and freight cost.
Just basic $.

Sand and minerals are very dense and heavy compared to light fibrous organic matter, pine bark, mill waste, recycled rubbish, etc.
This alone is the reason why you don’t ever see sandy material in the bagged potting mix anymore.

Instead, you see things like expanded clay, vermiculite, perlite, etc and they all have a high surface area that the soil biota needs to thrive, but only in theory…
The problem with them is they drain too much, or they hold water too well, or they blow away when dry, or they pack down and compress into a solid mass, or they turn into fine silty dust and completely disappear over time.
They all suck when you run a side by side trial and NONE are ever as good as basic river sand.
Due to the lower freight and production costs, all of them have fancy labels and are heavily promoted as a superior product.
This is based solely on lab reports of moisture conditions etc, not on real-world conditions.
I don’t bloody care what the lab reckons or the label says.
I only care about what works in the real world, where I live…

A nice soil mix that has some absorbent material, along with a healthy dose of granular sandy material, along with a little organic matter is best.
Like any creature’s diet, a plant’s diet needs BALANCE.

This brings me to my real pet peeve, slow-release fertilizer in commercial soil mixes.
These are those coloured balls and what they are is synthetic chemicals or very rarely mined rock minerals that have been coated in a soapy waxy substance that is designed to melt and break down at a very controlled amount over time.

Many very safe pharmaceuticals pills and capsules work the same way, dissolving at a controlled amount over time, releasing a steady amount of medicine.
If you ignore the medical advice and chew them up instead of swallowing them whole, then the dose of medicine is absorbed all at once. This can cause serious health issues and even potential overdose and death.
The exact same thing happens with a slow-release fertilizer in fancy commercial soil mixes!

In ideal conditions, they work ideally, and when quality control tested at the packaging facility everything is spot on at all the approved levels of nitrogen, potassium, ash, etc..

Yet here in the real world where I live, they are never in ideal conditions.
Soil is a cheap and very low-profit product but without it, folks won’t come to a garden centre to buy higher profit things like crappy Chinese-made garden tools, gadgets, or plants bought in bulk from wholesale suppliers.
That is where a garden centre makes its profit, it’s not from direct sales of bags of dirt.

Gotta have a variety of dirt to bring the customers in though, but due to price point, it’s never looked after both in transit, or when stored at the garden centres.
It is regularly exposed to excessive sunlight, wind-heat, which can all dry it out and melt the waxes used to make the slow-release fertilizer balls.
If rained on or waterlogged that also melts the fertilizer balls early than intended, acidifying the soil mix.

Even just basic compression from stacking pallets on the truck fractures and punctures a very large % of them, and as soon as they get wet they release the fertilizer far earlier than the manufacturer says they will.

  • It is a FACT that in ideal conditions they work great, I 100% agree.
  • It is also a FACT that they sample the soil mixes pre-delivery not post-delivery making those results totally meaningless.
  • It is also a FACT that the thing you are buying after it has been delivered and stored is NEVER as good as the manufacturer and fancy pretty coloured label says it is, and I’d happily bet my left nut on that.

Nitrogen is the major component of these pretty coloured balls, and it is the ideal energy food for a mature growing plant actively producing leaves. It is also super toxic to seedlings and it will both reliably prevent germination and/or kill them.
It’s like force-feeding a newborn baby a couple of kilos of sugar.
While technically it’s “edible” and it is considered a safe high-energy food source, it still ain’t ever gonna end well…

Mother nature knows best and plants have evolved over millions of years to the conditions mother nature freely provides.
If you want to make a nice soil mix then go and have a look at nice soil. Seriously, just go have a look.
You will always find a mix of organic matter, and sandy mineral grains, and a component of well-composted material for trace elements along with minor moisture retention.
That’s it.

No gels or waxes or binders or colours or volcanized rock or synthetic chemicals or any of that other crap, yet the plants are doing fine. Thriving even.

While it’s super easy to better this in a lab or research facility using man-made materials and a completely artificial set of climatic conditions, no factory or scientist in the world can ever do better in a real-world outdoor garden setting.
Never has, and never will, so just ignore the hype and fancy labels.
Save a heap of time and money by copying mother nature instead.

 My soil mix is as follows:

  • 2 parts of river sand. Don’t be a tool digging out the river banks causing erosion.
    Just take it from the flats and sand bars or buy it from a landscape supplier.
  • 3 parts well-composted pine bark, or well-composted timber mill waste, or well-composted recycled landfill green waste, or failing that cheap simple potting mix.
    “Black and gold” used to be a great option consisting of well-composted landfill green waste and pine waste but now it’s full of crap too, so these days I just buy mine in bulk by the trailer load.
  • 1 part very old, dry and crumbly, well-composted cow manure.
    Fresh, wet, or dark coloured manure is way too rich and nutritious and it will kill seedlings and/or prevent germination. Mine is very old,  tan colour and dusty, and it comes from a local roadside stall, after being collected from nearby paddocks containing grass-fed cattle. It has been in the sun and rain for a long time before being collected, and it is stored bagged in the shade after that for even longer.
    Because of this most of its nitrogen has been leached out and washed away so it only provides humus and trace elements, along with a minor amount of moisture-holding potential.

For seed germination, it is very important to mix this all very very well and then sieve it to remove all chunks, stones, sticks, leaves, etc.
Anything bigger than about your thumbnail.
If you don’t do this step these can create minor inconsistencies in temperature and moisture, or your precious seeds can wash to the side and under them when you water, never to make their way back to the light and successfully germinate.

My basic rule of thumb for seed plant depth is as follows.

  • Seeds of 2mm or smaller get surface sown in a very shallow depression then very very carefully watered in using a fine rose watering can. If you are rough the tiny seed will wash down the sides of your pots never to be seen again.
  • Seeds bigger than 2mm all get planted at about double their diameter. For example, if the seed is 5mm across, it gets put in a hole 10mm deep then watered in. If the seed is 20mm it gets planted in a hole of about 40mm then watered in.

The only exception is with large legumes like the leathery skinned peas and beans.
For them, I never go quite as deep as I do with other species and I no longer water them on the day of planting.
I always give them a day or two first and plant them more shallowly as they are far more prone to root rot and damping off.
If they swell too quickly the hard seed coat can fill with water like a cup.
When that happens the seed itself is underground sitting in stagnant water and this causes rot.
When allowed to swell slower and planted closer to the surface, this issue is avoided.

I use the same basic soil mix for everything I grow as it has always outperformed all the fancy way more expensive brands out there.
In my side-by-side trials using it in comparison to the fancy stuff, I got a much better germination % across hundreds of different species all from different parts of the world, coupled with a way better survival rate over a longer-term.

For that reason(as well as basic cost and convenience) I have now used it to successfully grow THOUSANDS of completely different plant species over the years.
Many of them being super rare, dozens that bloody “experts” said would never grow here.
I personally can’t recommend you ever use anything else.

That said your conditions and needs may be different as could your own experiences and results, and for that reason, you may completely disagree with everything I’ve just said.
If so that’s bloody awesome, I really truly reckon that’s super cool!

I initially had consistent failures and wasted years of my life doing what bloody “experts” advised me to do, or even worse, things they told me not to do, and for that reason, I reckon you probably shouldn’t believe me either.
In my expert opinion,  “expert opinions” normally suck!

You should always listen to them to get ideas and inspiration, but you should never actually BELIEVE anything until you see it happen with your own eyes. Instead, I suggest you run a few side-by-side trials and REALLY work out what works best for you in your little corner of the world.

Best of luck with it all, and if you ever see anything cool I would love to hear about it!!!