Lately, there’s been a lot of conversation around potting mixes, thanks to Tim’s Garden Centre running a potting mix experiment. It’s a great conversation starter—but like many things in gardening, there’s more to the story than meets the eye.
What Tim’s Experiment Highlights
Tim’s trial uses 8 different Australian Standard Premium Potting Mixes, with dwarf Cos Lettuce planted directly into the bags. It’s simple and visual, and it highlights something really important—not all potting mixes perform the same, even if they meet the same standard.
In fact, some mixes that performed well in a previous trial are struggling this time around, and vice versa.
What does that tell us? The Australian Standard itself might not be enough.
What Tim Didn’t Mention
While the experiment raises valid concerns about consistency, it leaves out some critical context that gardeners deserve to know:
How long had each bag been sitting on the shelf before purchase? Age impacts nutrient levels, moisture retention, and overall performance. Cheaper mixes tend to sell faster, so they’re often fresher. Premium more expensive mixes, on the other hand, might sit longer, especially in big box stores where stock turnover may be slower for a more expensive range.
Where and how was the potting mix stored? Potting mixes stored outside in all weather conditions start to break down faster. This breakdown attracts fungus gnats, which thrive in moist, organic material.
We’ve even seen discontinued mixes on shelves years after they were removed from production. Old, compacted, and improperly stored potting mix isn’t a recipe for success.
Understanding the Australian Standard
This raises an important question—what do the Australian Standards for potting mixes actually cover? Most people assume they guarantee quality, but in reality, the standards primarily focus on:
Physical properties (drainage, air space, particle size)
Basic nutrient levels
pH balance
What they don’t cover in detail is storage conditions or maximum shelf life. That’s a major gap, because even the best potting mix can deteriorate if stored poorly or for too long.
So, What is Potting Mix, Really?
This is a perfect time to go back to basics:
Potting mix isn’t just dirt in a bag—it’s a specially formulated growing medium designed to support plant roots in containers. It’s lightweight, well-draining, and holds moisture without becoming waterlogged.
Garden soil, on the other hand, is heavy, compacted, and often poorly suited to containers. This is something I covered in my blog Going Potty, if you want to dive deeper.
Why I Stock Searles Platinum Potting Mix (and Not Searles Premium Potting Mix)
Tim’s trial uses Searles Premium Potting Mix, which is a high-quality potting mix containing a blend of organic compost, humus, trace elements, minerals, peat, coir, and Zeolite, along with 8 months of Robust® Controlled Release Fertiliser. It’s a solid mix that meets the Australian Premium Standard, but at Trevallan, I go a step further.
I choose to stock Searles Platinum Potting Mix®, the apex potting mix designed for long-term success. It’s professionally formulated using only the highest grade ingredients and advanced blending techniques, honed over decades of experience. Platinum doesn’t just meet the standard—it exceeds it.
Searles Platinum Potting Mix (Stocked at Trevallan)
18 Month Controlled Release Fertiliser
Contains Searles Flourish® Soluble Plant Food & Robust® Controlled Release Fertiliser
Double Strength Penetraide® Re-Wetting Granules and Water Crystals
Enriched with Potash, Fish, Seaweed, and Volcanic Rock Minerals
Enhanced with Zeolite, Trace Elements & Minerals
Suitable for indoor plants, ferns, potted colour, hanging baskets, shadehouse plants, and more
This is why not all potting mixes are created equal—and why choosing a higher-grade mix sets your plants up for success from day one.
The Real Takeaway
It’s easy to blame a plant for failing, but the real culprit might be the mix it’s growing in—or how that mix was handled before you even brought it home. This is why expert advice matters and why I’m always happy to explain the differences between products I stock.
This isn’t about saying one retailer is better than another, it’s about educating gardeners so they understand that not all potting mixes are created equal. If we want people to succeed in gardening (and keep gardening!), they need honest, clear information, something the industry as a whole needs to get better at providing.
If you want to know which potting mixes I recommend (and why), visit me at Trevallan. And if you missed my latest blog about the true cost of plants and why expert advice matters, you can find it here: True Cost of Greenlife
Gardening success starts with good soil—and that starts with knowing what’s in your potting mix.