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 Soil Mix for the Tropics

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Number of posts : 705
Location : FNQ
Registration date : 2012-12-11

PostSubject: Soil Mix for the Tropics   Fri Sep 02, 2016 8:22 am

Hi all. I have been experimenting with a soil mixture to suit the challenging conditions of the Tropics. I have been using the standard shop bought Searls cactus mix for years with varying degrees of success. I have found that this mixture tends to be very good in the first few months then rapidly declines in quality there after. One of the most noticeable issues I have with this mix is that after a long dry spell the soil needs to be soaked for 24 hours to re-hydrate it. This is very time consuming and a little tricky to get right. Especially for cacti with large tuberous roots. I.e. Lophs, arios, astros etc. Also, due to the extended soaking times I have found that plant mortality rates increase. This is particularly true around December - January when temps are a steady 38 degrees with 95% humidity all day everyday.

My mix is as follows:

30 litres premium potting mix. Screen out all large organic chunks with a half inch screen

20 litres quincan gravel 10mm screened. This is a fantastic volcanic scoria gravel, mined from the side of Mount Quincan. One of our local scoria volcanoes. It has some very interesting properties. It holds and slowly releases moisture without making the surrounding media wet.

10-20 litres of coarse sand

5-10 litres of brickies loam.

My observations so far is that this mix is exceptionally well drained and dries out quickly. However, the quincan gravel tends to retain moisture and act as small moisture reservoirs in the soil. This results in a media that remains loose and dry but still sustains growth between waterings. The picture below is the mix I use for the Astro's. It has a higher organic percentage as astros grow rapidly and can handle more feeding. I add a heap more sand and gravel to the mix if I am planting ariocarpus or copiapoa as these plants are highly susceptible to root rot. I have re-potted almost 3/4 of my entire collection in varying combinations of these ingredients with only 1 fatality. A small astro seedling that was sick and damaged anyway.

Sneakiest Cephalopod
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Calm and Collected

Number of posts : 298
Location : Melbourne
Registration date : 2014-03-01

PostSubject: Re: Soil Mix for the Tropics   Fri Sep 02, 2016 9:46 am

Looks like a good mix.
Interesting that you use premium potting mix. I have always used the cheapest stuff i can find, reason being is I like to have more control over the additives and the cheaper the mix the less additivies.
I've tried a bunch of different formulations but am now down to a mix of sifted potting mix and some form of gravel not too fussy on which one in varying percentages depending on what I'm planting.
Trichs and echinopsis go in straight potting soil.
We'd be dealing with very different climates though, i had a bunch of cacti out in the rain over the full winter and only lost 2 ferro .. everything else was happy as larry!
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Number of posts : 13
Location : Melbourne
Registration date : 2015-02-05

PostSubject: Re: Soil Mix for the Tropics   Mon Sep 26, 2016 2:21 pm

Hi sneaky, i use a mixture of 2 parts 7mm scorria, 1 part cheap potting mix and maybe a little bit of coir fibre. Being in melbourne it can stay wet and cold for weeks but the mix is free flowing while as you said the scoria holds some water deposits but not enough to cause any health problems. Ive never understood the reason for using sand, someone care to explain?
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Number of posts : 825
Location : SA
Registration date : 2008-09-14

PostSubject: Re: Soil Mix for the Tropics   Mon Sep 26, 2016 7:42 pm

My place is not the tropics but I use mix of:

1~4 mm pumice sand-3
Organic base cactus & succulent mix in market-2

Pumice sand is costly but this mix works well for Astrophytum and Ariocarpus.
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Number of posts : 705
Location : FNQ
Registration date : 2012-12-11

PostSubject: Re: Soil Mix for the Tropics   Tue Sep 27, 2016 10:36 am

Cool. I guess the pumice would be lighter than the quincan gravel as well. My benches aren't the best so I might try pumice to lighten the load.

Sneakiest Cephalopod
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