SOILS AIN'T SOILS
Where to start on the monumental subject of soils?
How about at the beginning?
What is the basic definition of soil?
The dictionary says it is:
“the upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles”.
So when you go into your local retail landscaping supply company here in South-East Queensland and check out their different bulk soils what are they actually selling you?
There is such an array.
‘Premium Garden Blend’, ‘Organic Garden Soil’, ‘Platinum Garden Soil Blend’, ‘Ultimate Garden Soil’, ‘Trade’ soil, under-turf soil, top-dressing soil, top soil, fill soil etc etc ad nauseum.
Actually, in most cases what they are selling you is, broadly speaking, pretty much what the dictionary definition of soils describes. A blend (of varying percentages) of components that, as a whole, meets classification as a soil and more directly should meet (and hopefully exceed) the Australian Standard for soils (AS4419).
SO WHAT DO YOU ACTUALLY NEED?
Basically, the best ‘soil’* you can afford for the job you want it to do.
(but sometimes the best soil will be more than we budget for!)
This requirement does not change whether you are growing vegetables, laying turf, ameliorating (improving) your own site soil, planting raised podium/rooftop beds or preparing ornamental garden beds.
*I use parenthesis for the word ‘soil’ as when it comes to podium/rooftop blends in particular an argument could be made that growing media is a more technically correct term
AND WHAT IS THE BEST SOIL FOR YOUR PARTICULAR PROJECT?
In nearly all cases that would be one of the more expensive ones.
A classic example is this:
One large retail landscape yard sells a wide range of soils and the most expensive is just on three times the cost of the cheap ones.
This example is a great way to highlight how you get what you pay for:
ONE OF THE CHEAP SOIL BLENDS
One is described as a blend of “partially (my emphasis) composted green waste blended with various (again, my emphasis) soils suitable for most bulk installations”.
Their honesty is commendable. On their website they freely admit it will be affected by ‘slumpage’.
As the green waste continues to break down it will ‘slump’ or shrink.
There are potential issues with a soil blend that is only partially composted:
1. In some cases, slumpage can be quite significant. I have had discussions on this subject with a representative of a prominent growing media supplier and his suggestion was that in the worst-case scenario (not their own product I might add!) slumpage could ultimately exceed 30% of original product volume.
Minimising slumpage may be one reason why the retailer of this cheap blend incorporates ‘various’ soils with the (semi) composted green waste.
2. If the composting process is still on-going there will be heat generated. That is not good for plants. If you’re at a landscape yard and you want to check this out dig into the pile of bulk organic based soil blend in their bin with a spade and see whether it is hot to the touch or even steaming! If it is, best avoid it.
3. Nitrogen Drawdown. The microbes that are at work decomposing the organic matter have first dibs over the plants for the nitrogen (N) in the soil blend. This has the potential to leave your plants N deficient, at least in the short term.
4. As the soil blend breaks down it potentially becomes compacted (with a resultant reduction in the soils air-filled porosity) and hydrophobic (repels water).
Neither is desirable.
5. The weed Nutgrass. The potential exists for the seeds to be present, particularly with cheaper soil blends. Nutgrass is tough to kill.
In a perfect world all soil blends should be tested prior to despatch for what is technically termed ‘plant propagule’ (weeds such as nutgrass) but unfortunately that test requires three weeks incubation!
THE EXPENSIVE SOIL BLEND
Faced with only the choice of either the cheap blend or the expensive I would personally buy the expensive without so much as even blinking my eyelids.
But I should also add that although I might not be blinking, my eyes might be watering!
This soil blend is comprised of over twenty ‘ingredients’, and for the most part none of them could really be thought of as spurious or un-necessary.
The manufacturer/retailer describes this soil blend as un-compromising and ‘crafted’. Both descriptions work for me. Somebody really put some thought into this soil blend.
But you pay for it.
AND THAT’S THE DIFFERENCE
This little example hopefully shows, just like with most things in life, you really do get what you pay for.
Just remember, the growing media your plant is thrust into is vitally important to the ongoing health and vigour of the plant.
So, when you sit down to work out a budget for your next planting project, consider carefully what the growing media component should be and how much it costs to get a truly satisfactory long-term result.
What quantity, quality and type of soil blend is required is a subject that nearly always comes up during our consultations and we are happy to spend time taking you through this subject when we are with you on-site to help steer you towards the best solution for your needs.