Share your soil mixes please!

[Robb]

I am curious as to what soil mixes everyone uses for their cacti, and what ones tend to work better for certain types (e.g. Mexican as opposed to South American etc). Ultimately, I would like to better refine my mix, make different mixes that are less generic and are better representations of what might be found in cactus habitats, allowing for more robust root systems and natural looking plants. You all seem to get excellent results with the mixes you use and hopefully this will be a good starting point for my soil experimentation.
Cheers!
-Robb

[DaveW]

Trying to reproduce soils which plants grow in habitat does not always work in pots, for instance just as using yard or garden soil in pots does not function the same therefore special potting mixtures are used. Soil behaves much differently in a mass in open ground than in a much smaller pot. You need to be trying to produce a mix for potting that simulates how it drains in open ground, not exactly reproduce the soil itself.

Generally speaking North American cacti will tolerate a more alkaline soil, but South American cacti tend to prefer one on the acid side of neutral, but given as long as it drains and dries quickly enough, many mixes will suit.

The only thing I have seen done on soils effect on rooting was on tuberous rooted Thelocephala's, where the experimenter found that peat and soil based mixes produced more top growth but at the expense of smaller underground tuberous roots. Whereas mineral based soils, more like the quartz or granite based ones of their Chilean habitat, produced larger tuberous underground roots but less top growth.

Probably that's the reason then the Continental nurseries use peat based composts to produce maximum top growth, because as buyers can't see them you can't sell big roots! Some plants however always have more underground than on top of the soil.

A seedling Thelocephala nuda.

nuda.jpg (93.41 KiB) Viewed 3830 times

[Steve Johnson]

Trying to reproduce soils which plants grow in habitat does not always work in pots, for instance just as using yard or garden soil in pots does not function the same therefore special potting mixtures are used. Soil behaves much differently in a mass in open ground than in a much smaller pot. You need to be trying to produce a mix for potting that simulates how it drains in open ground, not exactly reproduce the soil itself.

Generally speaking North American cacti will tolerate a more alkaline soil, but South American cacti tend to prefer one on the acid side of neutral, but given as long as it drains and dries quickly enough, many mixes will suit.

The only thing I have seen done on soils effect on rooting was on tuberous rooted Thelocephala's, where the experimenter found that peat and soil based mixes produced more top growth but at the expense of smaller underground tuberous roots. Whereas mineral based soils, more like the quartz or granite based ones of their Chilean habitat, produced larger tuberous underground roots but less top growth.

Probably that's the reason then the Continental nurseries use peat based composts to produce maximum top growth, because as buyers can't see them you can't sell big roots! Some plants however always have more underground than on top of the soil.

Dave is correct -- container culture is so very different from cacti growing in the open ground. While trying to approximate native soils may be a fine idea in theory, I don't think you'll find any veteran growers who've been able to do it successfully.

Robb -- these links give you a fairly detailed description with regard to the "what" and "why" of my mixes:

http://www.cactiguide.com/forum/viewtop ... 25&t=37247" onclick="window.open(this.href);return false;

http://www.cactiguide.com/forum/viewtop ... &start=195" onclick="window.open(this.href);return false;

I concur with Dave on the difference in rooting behavior between mixes containing soil and soil-less mixes. I've found that aeration in "open" soil-less mixes is the key to optimally robust root growth, although if you can't get pumice (or you can, but the proposition will be too expensive for you), this may be a nonstarter. As to the "exotic" minerals some people use (and I'm thinking of the soil hexalog), I'm not sure if the results would be significant. Not for me, but for you it could be worth some experimentation.

[Robb]

Thank you both for your replies!

Trying to reproduce soils which plants grow in habitat does not always work in pots, for instance just as using yard or garden soil in pots does not function the same therefore special potting mixtures are used. Soil behaves much differently in a mass in open ground than in a much smaller pot. You need to be trying to produce a mix for potting that simulates how it drains in open ground, not exactly reproduce the soil itself.

Yes, I understand that pot culture is very different to open ground. What specifically I was asking about is what kind of soil composition might I encounter with different genera/species. Your information about soil pH for the different groups was interesting, and thank you for that picture and information about Thelocephala! It would be an interesting experiment to compare the root structure in organic and mineral based mixtures for other tuberous cacti such as Turbinicarpus. I think I may have some Turbinicarpus x seeds lying around so I think I might give this a go.

Robb -- these links give you a fairly detailed description with regard to the "what" and "why" of my mixes:

http://www.cactiguide.com/forum/viewtop ... 25&t=37247" onclick="window.open(this.href);return false;

http://www.cactiguide.com/forum/viewtop ... &start=195" onclick="window.open(this.href);return false;

I concur with Dave on the difference in rooting behavior between mixes containing soil and soil-less mixes. I've found that aeration in "open" soil-less mixes is the key to optimally robust root growth, although if you can't get pumice (or you can, but the proposition will be too expensive for you), this may be a nonstarter. As to the "exotic" minerals some people use (and I'm thinking of the soil hexalog), I'm not sure if the results would be significant. Not for me, but for you it could be worth some experimentation.

Those links are great, thanks Steve! I will have to give that soil hexalog a good read through soon as it seems exactly what I was looking for. I think your soil mix will be a good starting point for my experimentation, and while pumice is readily available here, I am not sure how easy it would be to get granite. I do have some coarse granite sand that I collected from a holiday, but I don't think that there is enough to for any large scale soil mixes.

Cheers!
-Robb

[DaveW]

Don't know about New Zealand Rob, but I get granite chips "6mm to dust", from my local builders merchant for only £2.06p for about a half hundredweight bag. The Building trade uses it in paving stones and steps to make them non slip, therefore it may be possible your main builders merchants stock something similar? A lot if the plants in Chile were growing in disintegrated granite and quartz soils.

[Steve Johnson]

Don't know about New Zealand Rob, but I get granite chips "6mm to dust", from my local builders merchant for only £2.06p for about a half hundredweight bag. The Building trade uses it in paving stones and steps to make them non slip, therefore it may be possible your main builders merchants stock something similar? A lot if the plants in Chile were growing in disintegrated granite and quartz soils.

Good tip, and I think crushed granite poultry grit should be easily available in New Zealand as well.

[mdpillet]

My base mix is 70% pumice, 20% sandy topsoil, 10% local compost (low fertility, low pH). pH is around 6.5. For species that likes their alkalinity I add limestone gravel.

[graffiti]

I'm a noob, but I'm having reasonably good luck with a mix of 4 parts NAPA 8822 (can't get pumice anywhere in southern new england, apparently) four parts 1/4"+ gravel, 1 part standard Lambert LM-3 pro mix.

And by 'reasonably good luck' I mean nothing has died from rot yet.

[DaveW]

Pumice is not that common in the UK, but I got my pumice off EBAY from one of the Bonsai merchants since they use it quite a bit, not cheap though as with anything bulky or heavy you can't obtain locally that requires transport in small quantities. When I try American EBAY it keeps switching me to UK EBAY so you will have to search yourself.

[Arc]

I have been cutting local creek sand and gravel with home grown worm castings, topped with whichever pretty stones I happen to find out there. I have a lace cactus that hasn't complained about the mix for 1.5 years now. The mix is roughly 75% silt and fine gravel to 25% home made potting mix. The potting mix is mostly worm castings, but its cut roughly 25% with peat moss and composted leaves to stretch it. The mix varies depending on what I plant, the desert cacti and my Madagascar Palm https://en.wikipedia.org/wiki/Pachypodium_lamerei" onclick="window.open(this.href);return false; get almost pure sand with some organic material. My Plumaria tree is cut more 50/50 with sand and bagged dirt. ( I ran out of home made stuff. )

My Trichocereus stock will likely get a mix leaning heavily to organic matter with some perlite and coco coir.

Only one cactus, a puny Opuntia / Prickly pear rotted from a month of rain (Texas), The endless humidity got a few of the fuzzy patches growing some black stuff but I've brought those back inside for a cinnamon dusting and recovery. The Opuntia was planted in pure sand. I try to keep all of my plants in Terra-cotta / clay pots.

My seed starting mix is roughly the same, sand mixed with potting soil, however my Fermosa seedlings are turning red with a concave circle ontop so the next batches are going in pure silt. I Microwaved, even melted a pot.

Amazon prime is a neat bit for shipping amendments, hard to beat free shipping on 50Lbs of coco coir. HA

[Robb]

Thanks for all your replies everyone! I gave the hexalog a good reading through last night and I must say I found it a very informative read! I would highly recommend it to anyone who is new to the world of cacti, or just wants to change their mix up a bit. I will try to find a source for granite this weekend as per Dave and Steve's advice, along with some limestone, lava rock, and river sand. I collected some maple leaves yesterday and have them composting in bag right now, but seeing as it may take a while for them to fully compost I may have to get some ready made leaf mould from a local beech forest.
Hopefully soon I can begin mixing my new and improved soils!
Cheers!
-Robb

[DaveW]

I also get limestone chips from my local builders merchant. They are used in the UK for covering felted roofs to keep the sun off to help stop cracking the roofing felt. Some only stock the larger size, but luckily my local merchant stocks two different sizes, some about quarter of an inch. Also in the UK there is a fad for using fancy gravel for paths which may be another source.

http://www.homebase.co.uk/en/homebaseuk ... -chippings" onclick="window.open(this.href);return false;

Don't know about Maple leaves, but oak or beech leaf mould is supposed to be the best.

[tudedude]

My standby is pumice and quality coir that has been rinsed. Pumice has silica which I believe certain cacti like? Who knows. Sometimes I'll add chicken grit or scoria to add weight.

[widea]

3 parts red granite gravel, 1 part small 5 mm grit, 1 part small 2 mm grit, 1 part perlite, 1 part cactus soil.
Once a year I add a bit of bone meal.
Here in Holland cacti planted in this soil mix even withstand prolonged rain (days) and the cacti seem to like it.

My soil mix part 1.jpg (37.41 KiB) Viewed 3469 times

My soil mix part 2.jpg (35.84 KiB) Viewed 3469 times

example.jpg (54.94 KiB) Viewed 3469 times

Regards,

Cor

[BenTheCactusFriend]

Been using the following recipe for about a year after reading the hexalog. It all depends on what you can easily get hold of. Bonsai dealers are good sources for unusual components. It took me literally weeks to source everything, and a lot of trial and error.

I try to get a good mix of 1/8 to 1/2 inch gravels. Nothing under 1/8 inch. The pine bark fines are only there as sort of "slow release organics".

2 parts crushed granite
2 parts pumice
1 part zeolite
1 part calcined clay
1/2 part pine bark fines

My only complaint is that when it's really sunny and hot out it will dry out very fast. Watering twice a few minutes apart really helps get more water into the mix.