What is considered "standard" potting soil?

[davidyjones]

Quick background: I have a bunch of Trich. Bridgesii that have never had rot issues. Have always made my own potting mix (60% pearlite, 20% filtered top soil, 20% filtered organic compost). Yesterday discovered every single one of my plants had some degree of rot. So I am starting over and want to make a better potting soil this time around because I have a feeling I have just been getting lucky the past few years with the rich potting soil that I've been using.

I am going to follow this soil guide as closely as I can: https://cactiguide.com/article/?article=article8.php

However, when it says 1 part "standard" potting soil, I am unsure of exactly what this means. I only have a home depot and lowes locally so can someone help me out and link me products from these stores that would qualify as "standard" potting soil. Additionally, will I need to filter this soil or can I just add it right into the mix?

If you need any other info from me please ask. I really appreciate any help/suggestions!!

Thanks,
Dave

[7george]

Every one means something different saying "standard" potting soil. Some mean that sold in garden centres under "cactus soil" tag and others mean their own mix being used for years to re-pot cacti.

My guess about the rot is different: cacti grown in Florida most likely originate from other climatic zones. So the cause for rotting is not only in soil structure but with other growing conditions: rain sheltering, watering schedule and drainage, air moisture, etc.

The standard soil can be different for different groups of succulents, like forest cacti, desert mexican & US cacti, high mountain cacti, south-american cacti and so on. If all of of above rot something fundamental is wrong in cultivation method.

[HudsonLH]

Dave,

I'm afraid that there is no standard potting mix I am aware of as most if not all brands vary their mixes.

RE rot: I have never had an issue with trichocereus rotting, even in the tropics where I now live. Given how light perlite is, it is possible that consistent watering has caused the medium rise to the top, in turn causing the heavier organics to settle at the bottom. This would mean, of course, that your cacti have been sitting in almost 100% organic material. Can you confirm this?

H

[MikeInOz]

However, when it says 1 part "standard" potting soil, I am unsure of exactly what this means.

Standard potting soil is used to describe what is sold as the potting mix you would use for general purposes (flowers, vegies, woody shrubs, indoor plants etc)
That could mean a 1 sand 1 peat 1 soil mix or a 1 composted bark 1 sand mix or 100% composted bark mix or 1 perlite I vermiculite 1 peat, or any other combination with all kinds of ingredients made up to suit various potted plants. Very generally, it is organically based. The quality varies from extremely good to extremely bad! Check for pH, salinity and maturity.

[DaveW]

"Standard" varies with time, the organisation you belong to and your country, plus as Mike says what is commercially sold as such. In the past in the UK the standard cactus mixes used to contain John Innes (JI) standard plant potting soils plus extra grit. But now even good old John Innes formula's have been adulterated commercially and some even claim to be "peat free" ,which is a farce since peat was an integral part of their formula therefore don't deserve to be called JI mixes. Now many are using purely mineral mixes and few go through their collecting lifetimes now without trying new mixes.

The only thing that remains standard for our potting soils is they should drain freely and quickly so as not to stay damp too long and be around the PH those particular plants prefer.

For those in the rest of the world that never heard of JI potting soil for "normal" plants, here are the formulas. British cactus growers standard mix used to be JI numbers 1 to 3 (they only differ in amount of fertilizer added) diluted with a quarter to half extra potting grit to aid drainage, but most have now moved on now to alternative mixes.

https://www.gardeningdata.co.uk/soil/jo ... _innes.php

The old fertiliser recipe in JI potting soils (we call them potting composts in the UK) is now usually replaced in commercial mixes by a normal balanced fertilizer.

[One Windowsill]

Experimentation with substrates has been going on for a long time. 88 years ago, in The Cactus Journal of March 1933, a discussion was reported:

At the meeting held on December 13th, Mr P. V. Collings introduced a discussion on "Soil versus burnt clay". Mr Collings began by saying that the only way to judge which was the right potting medium was by the results obtained. Cacti are plants which can put up with great hardships, but some people are apt to overdo it. The compost he recommended consists of a mixture of loam, mortar rubble and coarse sand, but no leaf mould.
The important thing with all cacti is drainage ; burnt clay, being very porous, certainly affords excellent drainage ; plants root very quickly in it and it is the safest material for rooting newly imported or damaged plants.
Mr. O'Donoghue began by giving sound advice ; if you are satisfied with your present potting material, don't change. Personally, he was using burnt clay because he found it difficult to reach all his pots and there was less chance of doing damage by overwatering.
Mr. Boarder considered burnt clay was very handy for people who only had limited time to devote to their plants, especially as it was often difficult in a town to get good loam.
Mr. Lambert said that he used burnt clay for all cacti and succulents and also for alpines. He thought it was very important to keep plants true to type ; lush green growth was not, in the case of cacti, true to type.
Several other speakers contributed to the discussion, which, though spirited and very interesting, was naturally not conclusive. There was a general feeling that anyone who had the opportunity should experiment with several types of soil and that it would be very useful if a further discussion on the subject could be held at a future date, when, it was hoped, more data would be forthcoming as a result of experiments.

https://www.jstor.org/stable/42785001

These adverts were in the second issue of the The Cactus Journal in December 1932:

Clayburn.jpg (99.21 KiB) Viewed 1324 times

[DaveW]

Yes I remarked on some of these in the past. The "Clayburn" advert was by the chap who used to cook it on a sheet of steel over a bonfire. They said after selling it his garden/yard was one foot lower when he finally left! LOL

The modern "clayburn" substitute is selected red clay Cat Litters or Seramis.

Buxbaum used to pound up red clay bricks and riddle or sieve them to a certain gravel like size and grow cacti in that.