Which cacti hate mineral soil?

[RichR]

It is my understanding that most of my cacti will do better in a mineral soil mix since they are mostly from The US and Mexico.

The echinopsis and epiphylums prefer a soil with organic matter, as do some Notocactus species.

Are there any cacti that will just not do well in a free-draining mineral mix (loam, Turface, perlite)?

[daiv]

I am pretty sure Vlani grows everything in 100% non-organic "soil". Just got to feed them.

[RichR]

How about you Daiv? Do you use a mineral soil for any of your plants?

[hob]

for me just the epiphylums get some organic soil ..............but i'm not good with them anyway the others get mineral soil

[RichR]

Thanks, Hob. Good to know how other folks grow their plants. I've been leaning toward using mineral mix for everything except my echinopsis when it comes time to repot.

[vlani]

I do not have Epis but I got one S. testudo pot. It is actually 10 or so seedlings, and this thing is a monster, and a happy one. All in Turface, to keep things simple
Easy plants will take mineral soil with no wink. They are easy after all. The only problem to foresee is excessive growth rate. Who needs some Echinopsis to grow 4x faster?

[fanaticactus]

It is also my understanding that some Gymnos do better in a somewhat richer mix with a slightly lower pH. It's best to read up on each individual Gymno as to its affinity for a richer mix, though. They can differ widely. One thing is a must: the soil still must be well draining.

[daiv]

My mix is more or less what is described here:

http://www.cactiguide.com/article/?article=article8.php

Vlani - I'm pretty certain that plant is NOT S. testudo, but would say S. pteranthus is more likely.

[RichR]

I do not have Epis but I got one S. testudo pot. It is actually 10 or so seedlings, and this thing is a monster, and a happy one. All in Turface, to keep things simple
Easy plants will take mineral soil with no wink. They are easy after all. The only problem to foresee is excessive growth rate. Who needs some Echinopsis to grow 4x faster?http://www.cactiguide.com/forum/userpix/1433_IMG_0407_1.jpg[/img]

Are you saying Echinopsis will grow 4x faster in an organic soil than in a mineral soil, or the opposite?

[vlani]

Everything grows faster with healthy roots, and proper porous mineral soil is the best way to ensure that.

You will have to use proper fertilizer and adjust your watering, but everything grows better in mineral soil.

Daiv - no not pterantus, unfortunately . Flowers are way small for it.
I vaguely remember seeds were marked as testudo, but I can be wrong. Will need to look up that old MG order..

[daiv]

Ahhh. the flowers are smaller than they appear - Then I'll bet it is S. validus

[iann]

Mineral soils don't lack nutrients and are not synonymous with what has become called semi-hydroponic media. Mineral soil simply means it isn't based on peat, wood, or anything else that was recently alive. The soil is your yard is mineral (usually!) and plants do just fine without being fertilised every day. If you want to just grow in rocks, pumice, perlite, or polystyrene balls, that's OK but it isn't soil.

It would be helpful if people distinguished the two things. I grow in mineral soil but it is not semi-hydroponic and it certainly doesn't have to be fertilised every single time I water, although that is a good habit to get into anyway.

An interesting area is the fired clay granules that many people use. Because they are made of clay they have the ability to retain nutrients just like soil and at least theoretically wouldn't need to be treated in the same way as completely inert substrates like pumice or perlite. I don't really know how this works out in practice.

[Steve Johnson]

Well, I hope I'm not adding fuel to the fire here...

RichR's topic on this thread got me little interested about the subject. Back in June, I started my new collection with cactus mix prepared by the California Cactus Center. Here's a sample:

I don't know what's in the soil itself, although it's mixed with gravel and maybe some pumice. There also seems to be a little organic material, but I'd say not peat or any of the wood products I'd expect to see at Home Depot, Armstrong Garden Center, etc. From the CCC's advice, I add in extra pumice with 20% for Astrophytums, 25% for my Cephalocereus senilis, and 30% for my Melocactus matanzus. I also have 3 Turbs, which I'm considering for 20-25% additional pumice as well.

I'm not sure if this sample is going to give us any useful info, but I'd be curious. The CCC has been around for 30+ years, and while I hope that they know what they've been doing, I don't want to take anything for granted either. I'm always willing to consider different opinions. (By the way, the CCC didn't seem to be unusually expensive. However, I'd kinda see a 30 lb. bag go down the tubes if it turns out that I may have to go back to the drawing board for a better cactus mix. Sorry -- I hope I don't mean to hijack this thread!)

Thanks!

Steve

[amanzed]

My understanding is that pumice is not completely inert... it is a volcanic rock, typically a porous, air-puffed, granitic rock. This does provide some minerals. Also, it's porous so it will absorb some fertilizers. It does have somewhat different chemical characteristics from scoria, which is also volcanic and air-puffed, but basaltic in origin.

Even though it's not inert, you DO need to fertilize more in pumice than in soil.

[iann]

Pumice is rock. CEC is virtually zero. Porous is not the same as CEC, which measures how well a substance holds nutrients (without water!) in a form available to plants. Degrading to release trace elements is not the same as holding nutrients for roots. Clay holds nutrients available for the roots and most organic materials hold even more. Most other things hold virtually none and you need to provide the nutrients in soluble form or there aren't any.

That CCC soil mix obviously has some fibres in it, but I can't tell what they are. And something that looks like pumice or perlite, but it seems too dark for perlite. There are plenty of experienced succulent growers and sellers that use (and sell!) awful soils. The cost difference can be compelling, not least because fluffy organic soils are so light while rocks and dirt are so heavy. Loam soils are easy to find but locating a consistent source in commercial quantities not so easy. It also seems like regulations in the US right now make it difficult to bag and sell anything that would be considered a good quality loam.