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[Melb, VIC] Creating a Soilless Mineral Only Mix or 20% Soil Mix Based on "Xerophillia: The Stone Eaters"

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After loosing too many of my indoor cacti to rust / rot I've decided to get to create my own mineral only mix based on Xerophillia: The Stone Eaters. http://xerophilia.ro/wp-content/uploads/2013/08/The-Stone-Eaters.pdf. From my experience it appears that growing cacti & succulents on bedroom & bathroom windowsils indoors in Melbourne, VIC is challenging longterm because of the regular condensation & therefore high humidity. It seems the regular cactus potting mix sold at either Bunnings or Garden World Collectors Corner is either full of bark chips or peat moss as well, most likely making a breeding ground for microbes that cause rust / rot. Pre sterlising this potting potting mix in either a microwave or conventional oven was not enough IME to fix the issue longterm only slow it down. Please keep in mind this is why I have created one of the most high drainage & quickest drying mineral mixes. If others are are interested in using the ingredients I'm using but are in a hotter & dryer environment (such as outdoors) there are simple things you can add to this mix. For example adding porus rock should increase water retention. The porus ones I find that were not too difficult to find that are spelled out in The Stone Eaters guide as having good mineral content were perlite, vermiculie & pumice. The first two being available at most Bunnings stores but keep in mind they are very light and especially the perlite is often complained about as it floats on water. Pumice is a little harder to find and a lot more expensive. I found it for 50 bucks for a big bag from Bonzai Sensation which in Narre Warren South, VIC. Otherwise if you want there are other Bonzai suppliers that ship pumice from ebay in Australia their bags are generally much smaller and shipping is around 20 bucks. Scoria or crushed brick maybe inert in terms of mineral content but might be another cheap additive to add water retention. This seems to be reletively easy to find at gardening or landscaping supply shops.


So after much reading, hunting and testing I've found the cheapest sources for my mineral only mix. I'm using crushed & screened granite, sandstone & bluestone rocks sourced from Daiseys Gardeing Supplies @ 7 bucks per 20kg bag. These are the exact items I bought:

1x 20kg bag of screened 20mm sandstone

1x 20kg bag of screened 10-14mm granite

1x 20kg bag of screened 7mm bluestone

1x 20kg bag of screened local topsoil


Note: If you want less than 20kg bags I think they sell smaller "sample" bags @ Daiseys in the inside shop area. Also the screened topsoil is optional for mixing a 20% dirt + 80% mineral mix such as for tropical cacti. Here's a link to where I bought everything: https://daisysgarden.com.au/screenings/10-14mm-brown-screenings/.

Midway Concrete seems to also have these 3 mineral rocks. https://midwayconcrete.com.au/garden-supplies/rocks/. Many of the other gardening and landscaping supplies I contacted have the bluestone screenings (often just called 7mm screenings or 7mm gravel for building road base) but often not the granite or sandstone. The sandstone is usually called "Tuscan Screenings" and the granite is often just called "10-14mm Brown Screenings".


Here's a photo of the mineral mix I've created using granite, sandstone & bluestone:




If you don't have those 3 rocks easily available at local gardening or landscaping supply shops, another option I found is mica-schist from Bunnings. The larger Bunnings sell N.Z. schist for 16 bucks for a 30-50cm slab. The stuff is faily soft and I found lots of pieces of crushed schist rocks from just looking down near the bottom of the palate. Should be able to get this for crushed stuff for free as they only care about selling it in a large slab. It's fairly easy to crush pieces of schist up to a smaller size for potting just using a hammer. Reccomended to wrap the stuff in plastic wrap or a bag and probably use something a bit more than just "safety squints" like either safety glasses or a face shield to protect yer peepers.




If you've read through The Stone Eaters you'll probably be aware that carbonates such as calcium carbonate or magnesium carbonate are generally something you want to either avoid or at least be aware of in your mineral or mineral & soild mix as they are reported to act as growth inhibitors for most cacti. With this in mind and having a f*ck all knowledge of geology or how to identify common carbonate rocks such as limestone or marble, I went with the acid test. Below in the photos, I tested with vinegar. This proved to be noticable enough with bubbling for carbonates if I put my hand or something behind the glass to give a bit of contrast. Better than vinegar is whatever stronger acid you have laying around. The bubbling will just be more noticable if you have something a little stronger than vinegar. I found diluting some supermarket citric acid or tartaric acid in water showed the bubbling reaction much better than vingar.


Here is some unknown grey stone chips that bubble like mad in acid which indicate they contain carbonates. Is this limestone, marble or dolomite?!? Like I said I have f*ck all geology identifying knowledge...




Here are some other partial fails in terms of products I tested. They are two different sizes of pebbles from Bunnings. The acid tests on the ones below reveal that some but not all rocks fizzed. It was not like the grey stone chips where every rock fizzed. On the ones below it was usually just some of the white stones that fizzed. This might only be a small percentage of the rocks so it might be okay depending on how much you want to avoid carbonates. I'm not impressed that it's marketed as pebbles for aquariums as I thought carbonates were exactly what aquarium owners were trying to avoid when buying rocks or at least with ones that have live fish in them.




I sieved out the stones (and rinsed away all bark) contained in the potting mix from Garden World Collectors Corner. The acid test was very similar to the pebbles from Bunnings. Only a few white rocks bubbled. If I was to make a guess I'd say maybe somewhere around 10% of the rocks reacted.




I guess this pretty much ends my guide or adventures in making my own mineral mix. Hopefully my cacti will be happier once they are all switched over and hopefully I'll avoid more casualties from my friendly cacti creatures dying pre-maturely from rot. I'll probably post any updates in the future if there's anything worth reporting as I've decided to go a more extreme route than what the authour of The Stone Eaters reccomended. He was saying that for cacti that have been babied with lots of organic matter and artificial fertiliser like all of that NPK crap to wean them off gradually. He reccomended something like a 20% dirt 80% mineral mix for the 1st season with a couple of fertiliser spays. I'm going against that reccomendedation and instead trying to switch all my cacti to soilless mineral only right away since it seems as I'm pulling them out to repot, many of them need their roots washed out anyway some even cut right off because of partial rust / rot. I'll have some dilute Seasol fertiliser just to help them initially. It'll be interesting to see how this goes.


Update 26-Mar-2019:

I've re-potted my 1st three cacti tonight in mineral only mix. The cacti all had their roots thoroughly rinsed of all dirt & the rocks where rinsed and boiled to remove any dirt & minimise microbes causing rot. I used roughly a ratio of 1:1:1:1 of mica-schist, sandstone, granite, bluestone. I don't have much of the mica-schist so once it runs out I'll just be using equal parts of the other 3 mineral stones.




Update 29-Mar-2019

Okay that's it I'm all in on this one! Over the last couple of nights I've worked tirelessly to re-pot my whole cacti collection into my soilless mineral only mix. Pics are below. Some cacti I had to scrape & cut sectons of the roots that looked too dodgey from rust. Finally all done except for one cactus that's in heavy flowering, that is until I hammersnipe more cool cacti from ebay! :)




Update 11-Apr-2019

I've bought a few more cacti & succs and am slowly getting around to rinsing/cleaning the roots from dirt and re-potting in soilless. Have tried to rescue a few too far gone from rot by grafting on some dragon fruit stock. Interesting to see if they go alright on soilless. More updates soon... I've also purchased some different Opuntias (prickly pears) & Pereskiopsis Spathulata (AKA Peskys) so we'll see how those fast growers do on soiless. Oh and the tiny Strombocactus Disciformus is the only one I did not rinse the roots. As it was so small and tiny with not much roots I was able to just pick out all the bits of bark with tweezers and pot him straight in the stones. In case you're wondering the air-tight tupperware containers in the centre contain an array of cactus seedlings (from Lophs to Ariocarpus, Ortegocactus and Strombocactus & more) growing on on the take-away tek. Using one of those cheap Chinesium USB camo heat mats and a warm white LED bulb on a timer they seem to have grown well from being planted in the middle of winter. :)




Update 15-Apr-2019

I've had some clay pots arrive and finally potted the last of a batch of the cacti & succs. This is new to me so any advice is welcome. The new batch of clay pots I had to drill holes in them with a diamond holesaw. I used water to lube the drill as reccomended but now after a couple of days every gazed surface has fine cracks in the glaze. There was a disturbing cracking/tinkling/glass shattering type noise that went for more than 2 days as the pots dryed out. Did I drill it wrong? Should I not have used water when drilling? Are my pot going to blow apart or is it just the cosmetic appearace that cracks?


P.S. The last pic is a close-up of a grafted Loph. Jourdaniana. The tiny spines are a dead giveaway.



Update 28-Apr-2019

In the last few days I've cleaned & re-potted up these Opuntias. As you can see two of them are monstrose & variegated. The regular looking one is Santa Rita & I'll be most interested to see whether or not I get the reported change to that unique purple colour in winter. My apartment stays pretty warm during Melbourne winter so we'll see if it changes colour indoors or not.


Edited by Raver Buddy
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Wow, this is really, cool. I'll have to read stone eaters again tomorrow

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Good job on the repotting. These look great in the mineral mix!

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I've now given away the last of the extra minerals and topsoil I was offering for free or trade. Just a note that if you don't want buy each type of rock or soil by the 20kg bag, I think Daisey's offer smaller sample bags. Otherwise you could end up with 80kg of rocks & soil like I did without thinking and then had to give away the extra stuff to friends.


Also note that the screened local topsoil from Daisey's is high in clay. I would not use it on it's own for any plants as after watering it packs down like glue and will most likely not allow enough drainage for water and air to get to the roots. I found that mixing it with the different size mineral rocks (bluestone, granite & sandstone) in a glass jar showed that even after many waterings there are still lots of gaps below the surface for water & air to get to the roots. A salvia cutting planted in this mix, indoors, in winter has so far survived and even put on growth (with the aid of a regular warm white LED bulb & timer). I think this maybe a good enough test for me to use this soil & rocks mix for any other plants that aren't cacti, when grown indoors. Just seems that this is a far better option for indoor plants that are not cacti as it's less likley to be a breeding ground for those annoying fungus gnats that buzz around after watering. Again the likley culprit IMO is all that woodchip or bark.

Edited by Raver Buddy
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A bit more expensive perhaps, there's zeolite and diatomaceous earth. I sourced some from Dr Greenthumbs, during their Boxing Day Sale (20% off). 
The zeolite makes a most attractive (and functional) top-dressing. The diatomaceous earth is said to discourage pests, such as those gnats you mention. 

I always check Bunnings for damaged bags of stone -- often heavily discounted. 

In my experience, stone-grown cactuses grow smaller (will actually shrink, if transplanting from soil-based media) but do seem sturdier. 

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