When people try to grow plants in containers, one of the most common pitfalls that I see, is the use of poor quality soil, or potting mix. Last summer I conducted a small experiment to demonstrate the importance of soil in growing great vegetables. It produced some very interesting results, and generated quite a deal of interest from my gardening community.
This summer, I expanded the experiment to cover a wider range of potting mixes. I also investigated a range of off-the-shelf fertilisers (mostly certified organic ones). This was to see what combinations might work well for your container gardening, for those of you limited to major hardware chains and local nurseries. I wanted to see their effectiveness at improving the plants’ ability to grow in poor quality soils. See my blog post on my fertiliser experiment for more information on this.
Potting mix experiment round two
In the first round of my soil and potting mix experiment I looked at only four different types of soil and how effectively they could support plant growth. This time I have compared 11 different types of potting mix and soils. Most of the varieties were purchased from “The Big Green Box” and covered a range of potting mixes, including premium potting mixes and certified organic potting mixes. I also purchased a bulk potting mix, and a veggie mix from Fulton’s, one of our local garden supplies centres. A summary of the potting mixes and soils are tabulated below.
| Potting Mix | Purchased From | Cost | Bag Size | Organically Certified? | Meets Australian Standard AS 3743? |
|---|---|---|---|---|---|
| Fulton’s Five Way Soil Mix | Fulton’s | $80 | Per Cubic Metre | No | No |
| Natures Soil Potting Mix | Nature’s Soil, Silvan | $6 | 25 Litres | No | No |
| Scott’s Pure Organic Premium Potting Mix | Bunnings Warehouse | $13.99 | 25 Litres | Yes | Yes |
| Earthwise Growing Essentials Multipurpose Potting Mix | Bunnings Warehouse | $2.45 | 25 Litres | No | No |
| Brunnings Tomato and Vegetable Growing Mix | Bunnings Warehouse | $3.99 | 25 Litres | No | No |
| Fine Farms Blended Cow Manure | Bunnings Warehouse | $3.95 | 25 Litres | No | No |
| Debco Organic Potting Mix | Bunnings Warehouse | $13.98 | 25 Litres | Yes | No |
| Fulton’s Bulk Potting Mix | Fulton’s | $240 | Per Cubic Metre | No | Yes* |
| Osmocote Professional Premium Plus Potting Mix | Bunnings Warehouse | $10.97 | 25 Litres | No | Yes |
| Osmocote Plus Organics Vegetable & Herb Mix | Bunnings Warehouse | $9.98 | 25 Litres | No | Yes |
| Yates Premium Fruit & Citrus Potting Mix | Bunnings Warehouse | $8.98 | 30 Litres | No | Yes |
*Update 22/10/20. At the time of purchase I was led to believe that the Fulton’s Potting Mix did not meet AS 3743. On 12/10/2020 I was contacted by a representative of Fulton’s (which was over three years since contacting the company for feedback via email). They have informed me that their potting mix does now meet the Australian Standard.
All potting mixes, except for the Scott’s Premium Organic Potting Mix were purchased no more than the week prior to the experiment being set up. The Scott’s Premium organic mix was a bag left over from my first experiment from last year. The bag had been sitting, opened, but under cover for 12 months.
I had only intended to use 10 potting mixes and soils. However, when purchasing the products for our fertilser experiment, I came across the Fine Farms Blended Cow Manure. The word “blended” piqued my interest and upon reading the product description, it sounded more like a growing medium, than a soil conditioner. So I decided to use this as an eleventh “potting mix” in my test.
Of the 11 mixes tested, four of them were the same products tested in my first experiment from last year:
- Fulton’s 5-Way Blended Soil
- Nature’s Soil Potting Mix
- Scott’s Premium Organic Potting Mix
- Earthwise Growing Essentials Potting Mix
What does potting mix that complies with the Australian Standard (AS 3743) mean?
Potting mixes can be certified to Australian Standard AS 3743. Redtick, or premium grade potting mix include a minimum supply of nutrients from fertilisers such as a controlled release fertiliser. They may also have and other additives such as water crystals and wetting agents. To ensure that the mixes conform to the Australian Standards, a number of different tests are completed on raw materials and throughout the manufacturing process. To use the word “premium” on the packaging, the potting mix must comply to this standard. Beware of companies labeling their product with synonyms of “premium” (such as “professional” or “superior”) as these usually aren’t compliant with the Australian Standard and can be misleading to the consumer. Premium potting mixes tend to be more expensive due to the accreditation process involved.
What does “organic” potting mix or soil mean?
When it comes to soil, there can be two uses of the word “organic”. Organic can simply refer to the carbon based, organic matter in the soil. This may have come from manures, leaf litter, woody debris etc. Most soils have a component of organic matter. Soils high in organic matter are great for growing vegetables.
The second use of the term “organic” refers to “organically certified soils”. These soils are certified to comply with one of the several organic certification standards. These soils are free from inorganic inputs and are suitable for growing organically certified produce. Organically certified potting mixes tend to be more expensive and often don’t meet the Australian Standard for premium potting mixes.
You’ll often find garden supply yards labeling their bulk soils as an “organic soil mix”. This refers to the fact that the soil is high in organic matter, not that it is organically certified.
Setting up the potting mix experiment
I purchased 20 punnets of capsicum seedlings whilst at Bunnings purchasing the various potting mixes for the experiment. These were all relatively the same size, in the same condition and appeared to have been sown at the same time.
Using each of the different potting mixes and soils, I potted up five of each of the seedlings. I tried to make sure that each soil had a seedling from five different punnets to reduce the chance of experimental error.
The potted-up seedlings were then placed in my greenhouse. The pots were placed out in a pattern to ensure that the 5 pots of each of the soils were spread across the shelf. Each pot appeared to have equal access to light and water. The automated irrigation system watered every morning with a fine mist for 5 minutes. After 6 weeks, I assessed the plants and took photos of the results.
Results of the potting mix experiment
I assessed each of the plants and recorded the colour of the leaves as well as the number of plants in each group that had set fruit. I also recorded the total number of flowers and fruit set on the 5 replicate plants combined. See the results tabulated below.
| Potting Mix | Colour of Leaves | Number of Plants With Fruit | Total Number of Fruit across the five plants | Other Comments |
|---|---|---|---|---|
| Fulton’s Five Way Soil Mix | Light Green | 1/5 | 1 | Weeds growing in 3 of 5 pots |
| Natures Soil Potting Mix | Dark Green | 5/5 | 16 | N/A |
| Scott’s Pure Organic Premium Potting Mix | Yellow | 0/5 | 0 | N/A |
| Earthwise Growing Essentials Multipurpose Potting Mix | Yellow | 0/5 | 0 | N/A |
| Brunnings Tomato and Vegetable Growing Mix | 2 x Dark Green 3 x Light Green | 4/5 | 6 | N/A |
| Fine Farms Blended Cow Manure | Dark Green | 3/5 | 4 | N/A |
| Debco Organic Potting Mix | Light Green | 0/5 | 0 | Flowers present, but no fruit. Tall and spindly plants. |
| Fulton’s Bulk Potting Mix | Light Green | 0/5 | 0 | One flower present, but no fruit. One plant showing evidence of disease. |
| Osmocote Professional Premium Plus Potting Mix | 4 x Dark Green 1 x Light Green | 1/5 | 5 | N/A |
| Osmocote Plus Organics Vegetable & Herb Mix | Light Green | 1/5 | 1 | N/A |
| Yates Premium Fruit & Citrus Potting Mix | 3 x Dark Green 2 x Light Green | 2/5 | 5 | N/A |
I also took photos of the plants. Below is an image of the best plant out of the 5 replicates for each soil type. As you can see there is a huge variation in the performance of each of the potting mixes.
So what does it all indicate?
Never underestimate the importance of good quality soil in growing your fruit and vegetables. Interestingly, price isn’t always a good indicator of quality. I found that some of the best results came from cheaper potting mixes such as Brunnings Tomato and Vegetable Growing Mix. As a general rule, the certified organic potting mixes performed fairly poorly. Which is understandable given they are not conditioned with inorganic fertilisers.
Keep in mind, that the premium potting mixes are only confirmed to support plant growth for the first three months. If you’re growing vegetables, and especially fruit trees, in pots, over an extended period of time, it’s likely that you’ll need to top up the soil nutrients. You may be interested in the second part of my experiment, which looks at a range of off-the-shelf fertilisers that you may like to try.
On 03/04/17 I contacted the manufacturers or suppliers of each of the products investigated and invited them to leave feedback in the comments section below.
Update 30/04/17: I have finalised discussions with Scott’s Australia regarding the performance of the Scott’s and Debco products in our experiment. See below for details.
Disclaimer: All of the products tested and materials used in this experiment were purchased by Leaf, Root & Fruit at full retail price. No incentives or sponsorship are received from any of the companies mentioned in this blog post.
Response from Scott's Australia regarding the performance of the Scott's and Debco products in our potting mix experiment.
After releasing the results of our potting mix experiment, Scott’s responded with a series of phone calls and emails. I provided Scott’s with information relating to some of the batch numbers of potting mix used and further clarified how the experiment was run. They provided this written response. We have a few comments regarding their response:
“Scott’s cannot ensure that the product used were appropriate for trialling based on the ages found. The data described is not a true reflection of Scott’s and Debco quality and provides a biased view we believe based on bag age alone. Therefore the integrity of this trial has been placed in jeopardy when the data is stacking 1 year old mixes against other unknown aged products.“
The trial run the year previous (Dec 2015-Feb 2016) was with the Scott’s Premium Organic, which was purchased the day the experiment was set up. It had the same results as this year. So I’m not sure that the shelf life did have that much to do with the poor performance of that product. This is unless it had been sitting in Bunnings for considerable time before I purchased it. However, Scott’s response indicates that this is unlikely to be the case, due to high turnover of their product. It would be ideal to test all potting mixes fresh off the production line, and compare apples with apples, rather than apples with oranges. However, this experiment reflects the actual use of this product by the public. If a true, premium graded product, performs as the consumer expects it to, then this shouldn’t affect the results.
“The Australian Standard recommends a best before use date. This is a process Scott’s has considered but also knows from 6 years of sales data that no growing media is available for sale in stores longer than 4 months from delivery date.“
Other than the Scott’s Premium Organic, ALL potting mixes used in the experiment were purchased in the week prior to the experiment being set up back in December 2016. I have receipts available to substantiate this. The Scott’s Pure Organic Potting mix manufactured on 19th February 2016 was 10 months old when I purchased it in December from the Hawthorn Bunnings Store. If potting mixes have such a short shelf life, then I really can’t comprehend why they are not applied to the bags. Otherwise, manufacturers are setting consumers up for failure. In many cases, consumers will not be using the potting mix the day they purchase it. It may sit in the garden shed for months or even years prior to use. I am trying to support backyard growers to be more successful when trying to grow their own produce. A shelf life applied to the potting mix could further assist my work.
“Aspects of our Pure Organic Premium Potting and Planting and Debco Organic were labelled as high priced and ineffective in growth. When comparing organic lines against non-certified you are making large comparisons that cannot be measured equally.“
This experiment looked solely at the performance of capsicum seedling growth in a range of potting mixes. There are plenty of other ways to assess performance. But I feel that this (admittedly simple experiment) is a great way to do this on a tight budget. Readers of my blog post are welcome to make their own decisions about which potting mix to use based on their preference for organic vs non-certified vs budget vs performance.
I would like to thank Scott’s Australia for their response. It has certainly been an eye opening experience and helped me to understand the industry better. It has also raised a few concerns for me regarding the consistency of potting mix quality and performance that each product may afford the consumer. I’ll look to repeat this experiment again in the future and would appreciate feedback from the public on how it may be improved to obtain even more meaningful results for my readers and gardening community.
Thankyou. What a clever experiment.
Glad you found it useful Milica!
Hi Leaf, Root & Fruit,
I’m starting my self wicking VegePod today and came across this project! Great review and well planned out and written.
Are you planning on another follow up review? And with the self wicking capability of the VegePod (or other self wicking vege beds) would the requirements of the potting mix be slightly different due to a constant water availability?
Looking at the table above the best performing potting mix seems to be Natures Soil Potting mix followed by
Brunnings Tomato and Vegetable Growing Mix.
From your experience, how do these compare to Searles Herb and Vege Potting Mix?
Looking forward to your early reply and keep up the great work!
Hi Glo,
At this stage we have no plans for follow up experiments, they were just designed to highlight the importance of the right potting mix. There’s too muhc variability within the same product for us to warrant more work. Plus it costs a lot of money for a small, family run business. Both the Nature’s soil and Brunnings mix have high organic content. So I wouldn’t use them in a wicking bed as it may turn a bit anaerobic. You want something with a higher sand content.
I have no experience with Searles, so can’t comment there.
Best of luck with the project
Duncan
Hi Glo,
I have just purchased a vegepod and very excited to get started BUT so very confused about what soil to use!!!
What did you end up deciding on? I look forward to your help
Sonjia
Thank you. This experiment and report is very helpful.
I’m glad you found it useful.
Happy gardening
Thank you for this experiment. Some of your results mirror my experiences with vegetable growing, and what I was already suspecting eg. higher price does not always ensure a better outcome of fruiting.
Hi Polly,
Thanks for your feedback. Hopefully you’ve managed to find a reliable product that suits your needs.
Good Luck and Happy Gardening!
Duncan
why is it so bloody hard to get a bag of compost thats actually compost these days, i know what you mean about the cow shit i noticed a bag of that yesterday all finely broken down and i was scared to smell it cause it didnt say composted but omg im adicted to the smell it smellt like rainforest soil or something such a nice smell, i think ive had enough of buying animal by products tho as a vegan.. might just go back to using dirt out of the ground untill my own compost is fully broken down, f u scotts whys it so hard to care about the people and test your product before you sell it, perhaps they thrive off wasting lives, they do have a long time partnership with monsanto maybe they just want us to fail so we have to buy food or something, conspricies lol im just upset sorry, glad to caonfirm with your research thankyou for sharing
Thanks for your thoughts Scotty. Yes, it’s a good idea to make your own compost if you have the sapce and facilities to do so.
Good Luck and Happy Gardening!
it is very possible that scotts doesnt know that certain barks are alleopathic, or that woodchips rob nitrogen and alter the ph of the soil which is non existent (lol), so no matter how much nitrogen u feed it it wont come out of the funk it just seems to make the dying happen faster
Hi Scotty, There are many reasons why their potting mix may not have performed well. Your theory on woodchips robbing nitrogen etc seem plausible to me. I suspect that the quality of the input may have had an impact, but as I said, so could many other factors.
Thanks for your thoughts.
Duncan
I am checking out soils and potting mixes because I am experiencing an epic fail in my new garden. I have a long and successful experience with gardening and put in a new garden December last year using Richgro soil and Richgro organic mix. Results are awful , in the first 3 months soil levels as expected were down a third (I had overfilled the garden beds)and the soil had either separated into sawdust or around the bigger plants impenetrable blocks of mouldy looking stuff. Nothing much was growing even with extensive fertilising. Couldn’t keep it wet either. Ive filled the garden beds up but the levels just keep sinking and I’m faced with pulling everything out and starting again. How do they get away with this and why wasn’t Hortico used in the test?
Hi Annie,
Sorry to hear that you haven’t had the best results. We conducted this test on a limited budget (as it was it cost us several hundred dollars in materials to run the experiment). So we didn’t have the budget or space to test every single potting mix product out there. As it is, I suspect that each batch of potting mix is going to give you different results anyway. The experiment is more to highlight the importance of using good quality (not necessarily expensive) soil or potting mix in getting good results in the garden.
Are you using potting mix to fill a raised garden bed? I would recommend that in future you use a bulk, premium blended soil to fill raised garden beds rather than potting mix. Especially if you have clay soil underneath. The negative charge of the clay soil may be why your potting mix is becoming very hydrophobic.
Thanks for sharing your experiences with us.
Best of luck with any future attempts that you make!
Duncan
Nice experiment. I just planted out 8 tomatoe plant seedlings in Bunnings tomatoe and vegetable growing mix and one in a potting mix from a local nursery in Hobart (Chandlers) which costs 3 times as much as the Bunnings. Two observations after two weeks:
1. All tomatoe seedlings in Bunnings soil show yellowing leaves especially at base and some show a discolouration and stunting of upper leaves on large plants. The seedlings in Chandlers soil looks good and just like the ones in adjacent garden.
2. The miniature capsicum plant in Bunnings soil looks fine as well.
I suspect that the Bunnings mix is not mature enough and as someone above suggests is robbing nitrogen from the soil. I am adding a liquid fish waste mix in an effort to correct this. It also seems that tomatoe plants which are very fast growers may have a higher nutrient demand than other vegetables which makes the choice of potting mix even more critical than in your experiment.
Hi Nic,
Thanks for sharing the results from your own trials. Interesting observations you’ve made regarding the tomatoes versus capsicum seedlings. It might be worth us investigating that further.
Please keep us updated on the progress of your trials.
Good Luck and Happy Gardening!
Duncan
Hi I need some help I am putting new garden beds in my garden and would like to know thats the best organic soil or blend to put in to it and that’s cheap I was looking into Brunnings 25L Tomato and Vegetable Growing Mix
But I dont no please help.
Thank you
Hi Maria,
I’d avoid buying potting mix or any other bagged soil to put into your garden beds. Instead order in a good quality veggie growing mix from your local garden supplies. It will be far more cost effective (and better for the environment without all those plastic bags). You’ll get much better results also. Ultimately though, you’ll want to be enriching your garden bed soil with plenty of good quality compost. This wil need to be done once or twice per year.
Good Luck and Happy Gardening!
Duncan
Thankyou i really found this article very interesting, especially as a new gardener
Thanks for the feedback John.
Good Luck and Happy Gardening!
Debco used to be a good quality mix. It seems to have deteriorated in quality since Scott’s took them over. Everyone I talk to about their mixes say that they use garbage such as sawdust to bulk up the mix. After having multiple plants go backwards or die in Scott’s & Debco potting mixes I have decided not to use them anymore. They often use too much soil wetter and even though they know that water storing crystals don’t work they continue to use them in some mixes. It’s just a marketing ploy to justify the increased cost.
If you do another test in future I’d be interested in your results with Better Grow potting mix which although not sold at Bunnings, is available at many smaller nurseries (in Melbourne anyway).
Were the pots in a row or bunched up? Outer pots could perform differently to central pots due to drying wind or heat. For more uniform results I would place pots filled with soil but no plants on the outside of the potted plants so that all plants are surrounded by other pots for insulation.
Thanks for the feedback Jon. It’s a great idea to you plant-less pots. Unfortunately in this instance we were limited on space in our greenhouse. So to counteract any issues, we placed the pots in a pattern rather than groups. This meant that each type of potting mix has some at the front, some at the back and some in the middle.
We’ll certainly consider using plant-less pots in the future. We’ll also consider testing Better Grow in a future trial.
Good Luck and Happy Gardening!
Duncan
Yes, Debco used to do a lot of R&D out in Tyabb and continuously tested their product batches as well as their competitors. To stay ahead on quality, they aged their wood and bark components longer and used better formulations which all added to the costs and overheads.. The disappearance of specialist nurseries with the advent of the major supermarket garden centres and then Bunnings forced them to cut margins to compete and then cut back on quality to survive until the owners were made an offer they couldn’t refuse.
Thanks for that great insight Trevor!
Thank you for the experiment. Testing was on products the average gardener is likely to buy at the big green barn. If some potting mixes deteriorate over time, a use by date should be voluntarily shown on bags by the manufacturer. Please offer and publish more of these experiments in th future. The Amateur gardener is getting ripped off.
Thanks for the great feedback Norma. We’ll be sure to conduct further experiments in the future!
It would be nice to see the results in graph format. E.g. bar graphs to more clearly and quickly evaluate the results
Hi Mike,
Thanks for the feedback. Given our limited time and budget to run these experiments, we opted not to go into too much detail measuring plant biomass, plant heights etc. Without these measurements, there’s nothing for us to graph. Instead we chose to rely on photographic evidence to provide a visual method of evaluating results. The main point being, that it is important to get the soil right if you want to grow your own food!
Good Luck and Happy Gardening!
Duncan
I find increasing amounts of plastic and rocks in potting mixes these days. I would love to see an experiment measuring this. I also had this problem with bulk premium veggie growing mix
We are experiencing quite a few reports of such contamination. It’s a shame.
At this stage, with a limited budget, time and labour resources we have no plans for more potting mix experiments. We have had great success with the Nature’s Soil product and never have any contamination in that product.
I have recently sent Searles an email but to date I haven’t received a reply. I bought Searles Advanced Potting Mix 60l from Bunnings & used it straight away. I have found it to be more like garden soil & it too water retentive making it gluggy. I haven’t found this with other brands of potting mix used in the same way.
In regards to the potting mix trial with commercial brands; there are some issues that should be considered.
The potting mixes with fertilisers added are at the greatest risk of pH change, due to the potting mix (being sealing in a plastic bag) being placed in locations at retailers where the bag often heat up. Thus inferring dumping of fertiliser from slow release prills (which response to temperature and moisture).
Found one mix used to be fairly alkaline (around 8.5).
All bags should be stored at a standard temperature (if fertiliser included); the lower temperature the better, so chemical reaction is minimised.
Had some young seedlings burnt after using directly from the bag (Assumed too much, along with misguided trust). Toxicity of nutrients can be an issue in bagged potting mixes
Carrying out both a pH and Salinity test to all mixes can sometimes be a good indicator of what going on with the mix.
Sometimes airing the mix can remove some of the gases that have built up in the bag. Either place in a wheelbarrow in the shade and turn a few times, or cut the top and place in a cool location.
Sometimes it is easier to get a potting mix with low to no fertiliser added; and add when you wish to pot up your plants. Otherwise there is a risk that one puts too much trust in the commercial brands.
I’m surprised that only a 1/3 of the mixes meet Australian standards
Hi Douglas,
Thanks for sharing your wisdom with us. Great last point about buying a potting mix with no fertilizer added and then improving yourself, we totally agree. Stay tuned for this summer’s trial of different composts and soil improvers. We are getting some very interesting results!
Seems so hard to find potting mixes that have none of the additives – one I know of has fertilisers, trace elements, gypsum, water storage crystals and coir and even this brand’s Garden Soil and Planting Compost has these and they are supposed to be used as soil amendments – all of which don’t do anything long term. I will go hunting for your trial on composts now. Interesting reading 🙂
I’m glad you found the trial interesting. It certainly is a challenge to navigate all of the potting mix options.
Happy gardening.
Duncan
Good call, I have had similar results and now use Searls Premium Potting Mix, it has a 12 month fertilizer, wetting agents and works very well. I am surprised you didn’t include Searls, hopefully next time , cheers
Hi Bob,
Thanks for the feedback. Due to a limited budget and space in the greenhouse we unfortunately had to limit the number of products that we trialed. Our selection of products was based on walking down the potting mix aisle of Bunnings and throwing a random assortment of potting mixes into the trolley. Given the outcome of the trial and the resulting comments from the manufacturers, I’m not confident that we would get the same results if we repeated the experiment. It doesn’t seem like there’s much consistency from bag to bag. The point of the experiment was more to highlight the importance of soil and that performance was not linked to cost. Glad you’ve had success with Searls, maybe we can try them in a future trial.
Good Luck & Happy Gardening!
Duncan
Same here. I love Searle’s Organic potting MIx. Unfortunately I can’t seem to be able to purchase it in Victoria.
I have also used Searles recently and have seen instant results!!
Thank you so much for this, I found it very interesting and informative. I do use potting mix and because i cant afford top grade organic(certified) I have been mixing a potting soil mix with the tomatoe and vegetable potting mix mentioned. I would like to be able to buy a load of certified organic soil. My only attempt at this was a disaster as the load delivered to me had flecks of a grey substance through it and the water would just sat on the surface. I have an acre so i mix soil from my forest and compost with potting mix to get more soil when i need it. However , I really appreciate you going to this trouble and would love to see a trial on organic soil as well. How to bypass all those plastic bags of potting mix.
Hi Sharon,
thanks for the great feedback and for sharing your experience with us all. We’ll certainly consider your suggestions for future trials.
Good Luck & Happy Gardening!
Duncan
This is great to know, thank you for you efforts.
It explains why I have had poor success with potted citrus trees in the past!
Thanks for the feedback Paul. Good luck and happy gardening!
Thankyou this information has been so helpful especially that potting soils need a use by date. Would additives help ,with older soil, like compost and slow release fertiliser?
Hi Chrysanthy,
Thanks for the great feedback. Additive will certainly help. Please see our other experiments involving different fertilizers and soil conditioners.
Good Luck & Happy Gardening!
Duncan
I would not recommend using Brunnings Tomato and Vegetable Growing Mix. Over the last two years Brunnings management has followed a cost-cutting regime. It is not the same product as it was two years ago. It now has all sorts of rubbish in it now like stones, paint flakes, pieces of building sheet and has no added nutrients. Put succinctly, Brunnings’ products are absolute rubbish today.
Thanks for the update Ty. Good to know.
You may have made an error. In the results you say 5/5 plants in Natures Potting Soil had dark green leaves, but in the photo the corresponding plant has light green leaves.
Thanks for the feedback Mic. Glad you are paying such close attention. I can’t tell if it is the light from the side window causing the issue in the photo, or in fact that I did make a mistake when recording results. Either way, I obviously no longer have the plants to go back and check.
Stay Safe & Keep Gardening!
Duncan
As a professionally employed groundsman I use a large quantity of potting mix and have tried most of the above…There is a distinct and much varied quality out there and the only one i would use and say is half decent is Osmocotes Premium plus..The major issue which i find
with all potting mixes is they start out great and they rapidly deteriorate and how quickly the soil basically dies and has zero water holding capacity in summer which stresses plants.This is very true to the likes of Brunnings Tomato and vegetable mix… Lets face it most of these mixes are soilless based and are just recycled green bin refuse being composted and sold back to us with nutrients added for the initial splash and dash growth then they fail..There is a BIG market awaiting to be filled for a “True” premium potting mix out there with the quality and longevity to sustain the expensive purchased plants we place in them.
Thanks for your insights Andrew. Very true.
Stay Safe & Keep Gardening!
The only commercially available product I find useful is the ZooGro produced by Melbourne Zoo…it smells beautiful! It’s a struggle to keep up with home made compost, so I buy this product often. Unfortunately not all nurseries stock it, but it is well worth hunting out. Apparently it’s produced from all the animal’s waste (except elephants!) plus garden waste from the zoo. Highly recommend .
Thanks for the great tip Anne!
Hi there, thank you for your two experiments – a thoroughly enjoyable read.
Would I be correct to say that the “Fine Farms Blended Cow Manure” ‘potting mix’ (by itself) did better then many of the established potting mixes? (or am I reading and seeing this incorrectly).
It would be interesting to know the NPK ratio of this manure.
Cheers,
Paul
Hi Paul,
yes it did seem to do better than some of the potting mixes. It’s not really “manure” in my opinion. Simply a bit of manure mixed with a lot of composted arborists mulch or green waste. I’d imagine that the NPK rations would different a lot between bags.
Stay Safe & Happy Gardening!
I believe you’re right. Any product with the word/s “blend-blended” has a lot of bark / chips mixed in to bulk them out.
You’re paying for for filler . Thanks fir great articles
As the saying goes, the proof of the pudding is in the growing. Your method could not be fairer and found the results very helpful. There are always glowing descriptions on the bags so its great to see ACTUAL results to make comparisons. Thankyou and cheers!
Glad you found it useful Anthony. Thanks for the feedback!
I have had some concern over the lack of good results when using locally produced potting mixes. Western Australia.
I feel too much woodchip is present. This has the effect of reducing nitrogen content in the potting mix. When purchasing potting mixes I now run my hand over the outside of the bag. If it feels very lumpy I pass it by. I now refuse to purchase any commercial potting mix. However I still purchase the odd bag of compost. These contain a smaller amount of woodchip. I blend this mix 2parts local soil 1part compost. I then add lots of cow poo, sheep poo and pelletized chook poo, blood and bone and a sprinkle of potash. The result, although early, is proving to be most encouraging. In fact 100% better. One more thing. All peelings from the kitchen are placed 2/3 down the growing pot.
Your experiment has directed me to a limited amount of commercial garden products which I may consider using in the future. Maybe.
Keep up the good work chaps. And thank you for this information. Regards Jeff.
Hi Jeffrey,
Thanks for the feedback and some great tips.
Good Luck & Happy Gardening!
Duncan
No mention of Searls mix, I been using this for 2 years and now my freezer is full of cauliflower, broccoli, beans beetroot,celery and more, been an eye opener for me, great product, I met mr Alan Searle in my shop in Kakadu, lovely man.
Thanks for the feedback Glenn. We have limited space, and budget and testing every product and brand out there is just not possible for us. When selecting products to trial we aimed for those that are most readily available to small space gardeners in Melbourne.
Good Luck & Happy Gardening!
Duncan
Worthy experiment to me despite what Scott’s was saying.
Would you please do this annually as new products emerges and maybe do comparison on popular flowers too ? Peonies, Roses, and Sweetpea. Sunflower (from seeds) might be good too as theyre thirsty for nutrients. Thanks and im glad i found this today, but im looking for best value for money medium for potted floeers.
Hi Josh,
Time, greenhouse space and budget are all limited for our small business. Given the outcomes of the last trial and the feed back from Scott’s I’m not convinced that the products are going to be overly uniform from one batch to the next. So any results that we get may not be reflective of the product for the whole year.
As for the flowers, we do utilise a lot of flowers in our landscapes to help create diverse ecosystems. However, the business focuses on growing food, hence the use of edible plants in our trials.
That being said, I’m more than happy to collaborate with others who can help with the space, labor and budget to make this an annual trial!
Good Luck & Happy Gardening!
Duncan
This is brilliant. I came across this while looking for indoor potting mix. Would be great if I can find some experiments in indoor potting mixes.
Thanks for the feedback Rabia. Our company aims to help people grow food, so our research focuses on edible plants rather than indoor plants. Hopefully you can find some similar work done on indoor plants elsewhere.
Good Luck & Happy Gardening!
Duncan
Hi. Great info. This experiment is great for east coasters, but if shelf life (& bag temps) are taken into consideration that would make them worse for us gardeners over here in Perth.
We have a Perth supplier and would’ve been great to see results of their product.
Hi Andrea,
Thanks for the great feedback. Unfortunately time, space and money are all limited, so we chose to focus on products that are specific to our local clients and followers. Whilst we would love to help gardeners all over the country (and the world!) keeping our advice specific to gardening in Victoria enables us to make it more accurate and useful for our locals.
Good Luck & Happy Gardening.
This information is very helpful to me as I often wondered why I can’t grow any vegetables or flowering plants in the pots. Thank you for posting your experiments online.
Thanks Claire. Good to read you find our website useful.
Duncan
Thank you for this analysis. I sometimes get soil improver (?) from Bettagrower at about $16-$20 per 15 kg bag (approx. 25 litre) and have wondered about how it compares with the cheaper products at Bunnings.
Have you come across Bettagrower products?
Hi Poh, no we haven’t trialed Bettagrower. There’s just too many options out there to try them all!
Interesting experiments and results. People who have used Kelpomix mulch have reported very good results. The Kelpomix seed raising mix is, reportedly, even better.
Thanks for the tip Frank
Thank you for the effort you put into researching the products and conducting the trial on potting mixes. I often stand looking at the bags of potting mixes in my local Bunnings store and wonder what the information really means. You have provided needed information and understanding of terminology. I would be interested to see if you have conducted a trial on composts and the results of that. Thank you once again. Kind regards Jill
Hi Jill,
We have trialed some “soil conditioners” but not composts. The trouble with trialing composts is that it is difficult to find consistent products. Eg not all mushroom composts are the same and many have not even been used to grow mushrooms. Without consistently formulated products the results are meaningless.
Hopefully you find the soil conditioner trial interesting.
Good Luck & Happy Gardening
Duncan
This is really cool! I’m privy to the scientific method. Based on this alone I’m going to go for the Brunnings red bag potting mix. Super keen as it’s cheap and outperforms its Bunnings-sourced competitors.
Hi Nick, thanks for the feedback. Good luck & Happy Gardening!
I’d just bought several bags of the Brunnings Tom & Veg Growing Mix prior to reading your test results, so was pleasantly surprised. Many thanks for taking the time and trouble to test the commonly available mixes.
Hi Peter,
Glad you found our article useful.
Good Luck & Happy Gardening
Just had a similar results with the premium product. Used the cheap tomato Bunnings product last year with great results…
I found out my own way that Scott’s is a crap product..
Thanks for sharing your experience with us all Steve.
Good Luck & Happy Gardening!
Having grown up on a smallholding in England with lots of experience growing plants for food I’ve had a bit of a disaster with my first crop Here in Australia. Reading this and seeing I have one of the worst performing mixes has gone some way to assuring me that it’s worth giving it another go.
Hi NRTY, glad to hear you’re keen to give it another go. Having also gardened in the UK, I’m aware that there are HUUUGGGGE differences. I’m sure you will be on a steep learning curve though.
Happy Gardening!
Great information for what to purchase. Do you experiment with private garden centres that just sell soils and their own labelled potting mix?
Hi Tracey,
Thanks for your question. This experiment was more about highlighting how important great soil is to ensuring strong plant growth. As much as we would love to, we unfortunately don’t have the staff availability, space or financial budget to test every available option out there.
Good Luck & Happy Gardening
Duncan
Thank you so much for this analysis. I am not suprised. Pity I can’t get deliveries from Nature’s Soil in Victoria. Seems like the only good product.
For 7 years, I grow many fruit, nut and some veges from seed. All the soil/potting mix and seed raising mixes I have tried have caused me untold germination and growing issues. They have poor nutirition and/or are loaded with fungus gnats and/or have fungus growing through the media. Osmocote seed raising mix used to be great, same with seasol seed raising mix. This year I have bought bags of both and theyre full of bits of wood, mulch and other kinds of rubbish. Same thing this year with the potting mixes and soils. So angry !!!
Going to have to order bulk bags of soil and compost from ANL or someone similar, because the bagged stuff from bunnings is crap!!!!
Full of rubbish and diseased!
Hi Sleepy Fisher,
Thanks for sharing your experience (albeit a frustrating one). There are a few retail suppliers of Nature’s Soil in Victoria, but yes, it is hard to come by. They focus on supplying a quality product to the nursery industry but hopefully they branch out into retail in the future.
Good Luck & Happy Gardening
Duncan
I am wanting to put a hydrangea cutting into a pot (34cm x 34cm 30cm deep) to obtain blue flowers> The cutting has been in a small pot for about six months and the intention is to put in the pot during this spring (the earlier the better). What is the best potting mix to use to gain a low PH? We previously were given a hydrangea which had blue flowers but when placed in a pot and then in subsequent years the flowers were always pink despite using commercial products to try and lower the PH level. That plant has since died and we do not want to go down the same path and end up with pink flowers.
Hi Francis,
We focus on edible gardening and therefore don’t have a lot of experience with trying to find potting mix with a very low pH. The exception being blueberries which also need a lot pH. We find the Nature’s Soil supports fantastic growth and productivity in Blueberries, so I assume it is on the acidic side of neutral. Whether it is acidic enough for blue hydrangeas I’m not certain. In any instance many of the nutrients will leach over time an the pH may alter (as you have found). It may be better to be content with pink hydrangeas!
Good Luck and Happy Gardening
Duncan
This is how my tomato growing season is progressing in Melbourne at the end of January. Following your evaluation of the selected potting mixes I decided on the Nature’s Soil Premium Potting Mix in 40cm diameter black plastic pots (around 30cm deep). I planted seedlings in early November and watered the soil only as needed. I have applied Seasol Power feed, around half a capful as well as Potash, around a third of a capful in a bucket (9 litres) around every two or three weeks from planting.
I have five plants.
Diggers Tigerella currently very green leaves, 1.5m tall, had 66 flowers, for 25 fruit, 6 almost ready for harvest.
Diggers Mortgage Lifter green leaves showing signs of stress, 1.5m tall, 51 flowers, 6 tomatoes someway off harvest.
Diggers Aunt Ruby Green, lighter green leaves, 1.6m tall, 34 flowers, 9 tomatoes, late fruit set.
Diggers Granny’s Throwing, healthy green leaves, 1.2m tall, 27 flowers, 8 fruit.
Diggers Black Russian, some yellowing leaves, 1.3m tall, 60 flowers, 9 tomatoes to date. Still very green fruit as with most of the plants, except as mentioned the Tigerella.
Flowers are still being produced so hope to improve on the above numbers before the end of season.
So I am reasonably satisfied. My previous attempts have been a little tragic. More research was undertaken before my current effort.
Hi Bill,
Glad to read that you’ve had success with the Nature’s Soil Potting Mix. The descriptions of your tomato plants indicate that most of them are doing well (especially compared to your previous attempts). It is interesting to see the variability between varieties and that variability is reflected in my own experiences. That is, genetics or seed selection is critical to successful gardening. Some varieties are better than others for disease resistance, yields, timing of fruiting and most importantly…. flavour!
Keep up the good work and thanks for sharing your experience with us.
Duncan
I have always purchaswd osmocote premium mox and have alays liked this product for pots,but recently I have found it complete rubish with mainly bark not much soil I was wondering what has changed and what is the best soil for pots as I have tried seasol potting soil as well and it was like sawdust no body to it at all.
Hi Cheryle,
That’s disappointing to read that you are having issues with potting mix but something that I am hearing all too often. I don’t think there’s much control over what goes into most bags of potting mix. Late last year we purchased a premium bag of potting mix to demonstrate during a workshop how to set up a bioassay to test for herbicide contamination in compost. We had some strange results and it turned out the potting mix was contaminated with herbicide!
We have had very reliable results with Nature’s Soil. The product is consistent every time and all of our plants seem to thrive in it.
Happy Gardening
Duncan
Your conclusions pretty much reflect my personal experience with potting mixes. I have grown vegetables in a variety of large home gardens for over thirty years, in various places on the east coast of NSW. I buy a potting mix for drainage and low price and then add my own compost and nutrient selection because commercial potting mixes out of the bag will not grow a healthy plant. Brand name and reputation are not reflective of effective product.
Hi Max,
It sounds like you are on the right track by using the potting mix as a base and then amending to suit whatever you are growing. Well done and thanks for sharing your experience.
Duncan
Be good to know which ones are chemical free. Another experiment with Bunnings own brand which I find quite good and Buy Right brand from Mitre 10 would be good to compare too.
Hi Linda, how do you define “chemical free”? Do you mean certified organic? I’ll keep those two products in mind if we do a future trial.
Happy Gardening
Duncan
Brilliant article!
Great advice, I’m a first-time Tomato grower in grow bags, so thanks for all the information.
Keep up the good work.
My regards
Glad you found it useful.
Happy gardening!
Thanks a lot for the review of potting mixes. I have long been usspicious of how potting mixes are labelled and priced. Your experiment has demonstrated that reputation and “words” writen on potting mix bags means little.
My only problem now is locating some of the top ranked mixes out there….
Hi Colin,
Thanks for the great feedback. I’m convinced that if I ran the experiment again today, with the same products, that I would see completely different results. There’s just no consistency in the product. The most reliable product I’ve found is Nature’s Soil, but it’s next to impossible to find in retail outlets.
Happy gardening
Duncan
Thank you for a most helpful article
Thanks for the feedback, I’m glad you found it useful.
This is a great article and it would be good if you could include other brands, like Richgro Black Marvel, Searles, Scotts Osmcote in the orange bag.
Hi Lynn,
Thanks for the great feedback. I’m looking to do another trial “soon” and will be asking for suggestions about which products to include. Stay tuned to my newsletter for more updates.
Happy gardening
Duncan
https://www.productreview.com.au/listings/scotts-osmocote-premium-potting-mix
Seems to me that 37 out of 40 reviewers gave this product the lowest possible rating of 1.
Many talked about plants dying and the potting mix smelling.
Not sure I’d want to try based on those reviews.
I think your photo backs up that kind of feedback.
Thanks for the work you’ve put in to highlight this issue.
I’m glad that you found it useful. Thanks for sharing the link to the reviews.
Happy gardening
Duncan
Another simple test of potting mixes is pH. According to current internet wisdom. a slightly acidic growing medium is best for most plants. Acid loving plants require a higher degree of acidity. Most of the potting mixes that I have tested are alkaline, including Scotts Osmocote Rose, Gardenia and Azalia Premium Potting Mix for acid loving plants. My latest test of the pH of this product was on July 22, that is, yesterday, using a Manutec Soil pH test kit from Bunnings. The potting mix and the pH test kit were purchased yesterday.
There is little information of any substance about potting mixes on the internet.
Hi Allan,
Yes, pH is a good test to conduct. However, from my understanding, those simple pH test kits are not designed to test samples that are high in organic matter. If the test sample is for example, high in compost (or compost itself), or in the case of potting mix, high in composted bark or other organic matter, then the result is likely to show as being more alkaline than it actually is. That is, the result is misleading. To test the pH accurately they’d need to be sent off to a laboratory for analysis.
Thanks for your input.
Duncan