Potting mix basics
Potting mix is the essential growing medium for plants in pots. It provides everything they need grow, flower and fruit to the best of their ability.
Potting mix is a man-made soil substitute that is used to:
- Physically hold plants upright.
- Provide an aerated medium for roots to grow through to anchor plants in position.
- Absorb and retain water and plant food that roots can take up.
- Allow excess moisture to drain away freely.
- Supply food for plants via fertiliser included in the mix.
Cheap premium potting mix
That old saying that "oils ain't just oils" applies equally to potting mixes. When it comes to growing superior quality plants in often expensive pots, why skimp on the cost of the potting mix? Cheap potting mixes will not produce the results you expect and they will not last.
It is well worth the extra few dollars to buy the best premium quality mix you can. We're talking just a few dollars here - maybe only $4 extra a bag - but it will be money very well spent.
Look for the Australia Standard's FIVE TICKS logos on our Scotts Osmocote Professional and Debco bags to know you've chosen the best potting mixes money can buy. Red for premium and superior mixes that include controlled release fertiliser and wetting agent, and black for 'regular' mixes without controlled release fertiliser or wetting agent.
Cheap potting mix
✗ Is often made from uncomposted wood shavings or sawdust and sand.
✗ Has no texture, no structure and only minimal nutritional value.
✗ May be very acidic (low pH unsuitable for many plants).
✗ Does not include controlled release fertiliser.
✗ Compacts or 'slumps' in pots within a few months.
✗ Is badly aerated, starving roots of oxygen.
✗ Does not contain wetting agent or water-storing crystals so is difficult to re-wet if it dries out.
✗ Does not comply with the relevant Australia Standard for growing media.
Premium potting mix
✔ Is made from quality raw materials.
✔ Lasts for up to two years without compacting ('slumping').
✔ Is thoroughly composted to eradicate weeds, pests and diseases.
✔ Has good structure and texture, with air porosity that allows roots to take up oxygen (essential).
✔ Contains controlled release fertiliser to feed over several months.
✔ Includes a professional grade wetting agent to aid moisture penetration and retention, while still providing good drainage.
✔ Has a pH in the range of 5.9 to 6.2 - suitable for most plants.
✔ May include a 'bio stimulant' to give plants added strength and vigour.
What's in our quality potting mixes?
Australian potting mixes are rated as among the best in the world because most of the well-known brands like Scotts Osmocote and Debco are manufactured from the best quality raw materials we can source and the finished products comply with the Australian Standard.
Our superior and premium potting mixes are made from:
- Composted pine bark (a renewable and sustainable resource).
- Coarse sand or grit to improve aeration and drainage.
- Coir fibre to hold moisture and nutrients (a renewable and sustainable resource).
- Wetting agent to improve moisture penetration and retention.
- Controlled release fertiliser to feed plants for many months.
Some mixes may also include perlite* or vermiculite** to make them lighter - ideal for very large tubs, vertical gardens or rooftop situations where the weight of pots, wall hangers and potting mix is a serious consideration.
* Perlite is non-crystalline and occurs naturally. It has the unusual property of greatly expanding when heated and is very light in weight.
** Vermiculite is formed from two natural minerals, biotite and phlogopite, which expand and exfoliate to form a light, flaky material when heated.
Why potting mix, and not soil from the garden?
Some people make the mistake of thinking you can simply dig up a few spades of soil ('dirt') from the garden and use that in a pot. That's not the case!
When growing in the open ground, a plant's roots have the space to grow down deep into the soil as well as extend out from the trunk as far as they want, giving them a huge volume of soil from which to extract food and moisture.
An average sized pot around 180mm in diameter, for example, filled with soil straight out of the garden:
- Will contain almost no nourishment.
- Will not absorb or hold water well.
- Will be poorly aerated, meaning roots suffocate.
A plant potted in it will not survive for very long.
The same volume of potting mix in the same 180mm pot, on the other hand:
- Will contain fertiliser.
- Be well aerated.
- Will contain coir or organic matter that will hold moisture and nutrients.
In summary, comparing the same pot size:
✗ Contains minimal nutriment.
✗ Retains minimal moisture.
✗ Frequently poorly aerated.
✗ Sets hard when it dries, becoming impenetrable to plant roots.
✗ Naturally organic-deficient.
✔ Has added long-term fertiliser.
✔ Includes coir and/or wetting agent to improve water holding.
✔ Graded bark sizes allows good porosity for aeration.
✔ Has mix of particle sizes that prevents 'caking'.
✔ Composted ingredients are organic-rich.
How is our quality potting mix made?
Composted pine bark is the main ingredient in most quality potting mixes. The bark is a by-product of the plantation timber industry - so it's local (not imported), renewable and sustainable.
Transforming pine bark into potting mix takes a number of processes:
- Pine bark is milled and screened at our facilities to produce different sizes/grades for different mixes.
- Screened bark has base fertilisers added and mixed through it to initiate composting.
- Bark is then formed into wind-rows (long heaps) outdoors.
- Wind-rows are turned over regularly to ensure even composting.
- Composting generates heat - the preferred temperature in the wind-rows is about 60 degrees C, which kills weeds and pathogens.
After two or three months when the bark is completely composted and resembles a rich, dark soil, other ingredients (coir, sand, wetting agent, controlled release fertiliser, etc) are added according to specific recipes for our range of individual mixes, eg Scotts Osmocote Professional Terracotta, Tub & Vertical Garden, Scotts Osmocote + Organics Vegetable & Herb Mix.
Each potting mix variety is then bagged, palletised, wrapped and delivered direct to retail outlets, ensuring that what's in store for you to buy is as fresh as possible.