Perhaps a very amateur question.

[benny989]

So I stumbled across some info that I wanted real opinions about, not just the generic "use well draining soil". At the moment my soil mix for my cacti is basically one part sand, one part perlite and one part cacti potting mix. The info I stumbled across was that you shouldn't use sand or ANY sort of potting mix, only a "grit" mix. The photo of the grit mix looked like crushed rock, which is obviously great for drainage but how on earth does the plant get enough nutrients without any sort of finer particles?

Basically, my question is, is this a real thing and how well does it work? Maybe we could post some pics of our potting mixes? Any tips would be greatly appreciated as I love experimenting with different things

[DaveW]

Basically they mean particle size. There are scales for particle sizes:-

http://pubs.usgs.gov/of/2003/of03-001/h ... /chart.pdf" onclick="window.open(this.href);return false;

Many of the very open purely mineral mixes collectors are now using without finer soil particles are verging on growing plants hydroponically, in that they use half strength fertiliser at most watering to provide the nutrients. Soil is formed from the breakdown of rocks anyway to form sands and silt thereby releasing their nutrients, plus also decomposed organic matter. No doubt there may be some release of nutrients from things like Cat Litter which is simply baked clay and maybe even sand and grit, though this may be minute.

If your mixture works for you stick with it, you only need change if you have problems. Different mixtures work for different growers. If you are in a very hot country your soils may dry out quicker than they would in a colder one like the UK, therefore we need to add more grit to make up for the slower drying time. Also soil in pots does not behave like soil in open ground where water sinks quickly to greater depths away from the plants roots. That is why you don't use the same soil in a pot in which the plants will grow quite happily in the yard or garden.

The problem is we all keep changing potting soils in the hopes we will find the magic mixture our plants will grow twice as well in, unfortunately you seldom find it. The other question is what sort of growth are you after? Some people like a lot of luxuriant top growth from rich mixes, whilst others prefer the harder more habitat type growth more "hungry" mixes provide.

[kristian_Fossmo]

This is what I use, planing on getting some smaller size burned clay in the mix in the future maybe, but this is working good for me so far. There is smaller bits of scoria (red) underneath, and I tend to remove some of the larger scoria bitts now... As for nutrient, as soon as you put a plant in a pot it is artificial breathing anyway, regardless of particle size. The most important things seem to be relatively quick drying time to prevent rot, good aeration of roots also seem to be a key thing in cultivating cacti, take a look at viewtopic.php?f=31&t=34730" onclick="window.open(this.href);return false; and you will se what a airy mineral mix will do, I let the pictures speak for them self... With that said, some are successful with adding organics as well, so everything is linked to cultivation technique and climate...

Pumice, scoria and granit

DSC_2778.jpg (69.87 KiB) Viewed 1537 times

[Steve Johnson]

The most important things seem to be relatively quick drying time to prevent rot, good aeration of roots also seem to be a key thing in cultivating cacti, take a look at viewtopic.php?f=31&t=34730" onclick="window.open(this.href);return false; and you will se what a airy mineral mix will do, I let the pictures speak for them self...

Thanks so much for the reference, and my post at the bottom of that link is a decent description of what I've been doing. For those of you who may find it useful, I'll just add a couple of things:

1. Granite is granite, and there's nothing magical about DG. If you can't find it, then crushed granite poultry grit will do the job, plus it's not that hard to find.

2. Residual fines in the mix were more of a problem than I realized when I put up that post on January 18. Long story short -- if you're going with a soil-less mineral mix, be sure to thoroughly rinse it before use. Give your cacti clean, open mix, and they'll thank you over the long run. (Over the short run too. After I started cleaning up my act about a year ago, the improvements have been pretty amazing!)

Pumice is perfect due to its unique combination of open porosity and good moisture retention. The only drawback to going soil-less (whether it's straight pumice, a pumice-granite mix, or something like Kristian's mineral mix) is that you'll need to fertilize every time you water your cacti during the growing season. You'll find opinions on ferts all over the place, and while I could put my 2-cents' worth in now, I'd rather wait until I can integrate this discussion into something a bit more comprehensive than what I posted in January.

Benny, you asked an excellent question -- all cactus & succulent growers have to start out as rank amateurs, and I think you'll find that this forum is a much better resource than anything else you'll see on the Internet. Glad you found us, and I hope the advice here will be helpful to you.

[benny989]

Wow. How interesting. Thanks for the great replies everyone. Thos is why i asked here first before going out and changing how i do things. I think I'll try repotting a few first and see how they go until next growing season, there's definitely a few cactus i have that i think will benefit greatly from this. Thanks again guys

[benny989]

Just had a thought; When watering a grit mixture like this with fertilizer (I'm assuming perhaps some sort of seaweed solution?) is it OK to catch the run-off and reuse the next time the plants need watering? Just wondering if the liquid fertilizer or even maybe something in any slow release fert in the grit mix might go a little bad if sitting around for a few weeks? Usually I try and reuse as much run-off water as possible but never anything with liquid fertilizer in it.

[kristian_Fossmo]

Reusing water is a good vector for disease spreading. I do not use fertilizer with every watering. I believe that when the water evaporates the nutrient salts stay in the pot mix, so next time you water, they dissolve again and can be used by the plants, gradually reducing in concentration. I have no reference to back that claim up, but it seems so plausible so I need to be proven wrong for changing my mind on that regard

[DaveW]

Frequently reusing the same water draining from the plant or letting the plant stand in it until it is reabsorbed can cause a build up of salts. The plant tends to selectively use the chemicals in the fertiliser or soil using some more than others, therefore if you keep pouring the same water back in the plant the least used chemical can build up to toxic levels. That is the reason, as Kristian says, to occasionally flush the pots through (known as leaching) with fresh clean water allowing it to run to waste rather than fertilising every time to flush out any residual salts building up.

As to granite chips I get mine from my local builders merchant in the UK at a fraction of the price Garden Centres would sell it, it is sold as "quarter inch to dust" or now the metric equivalent. It is often used in concrete for toppings for steps etc to give them a bit of grip. As to the dust you can either wash it out or look on EBAY and get something like a bonsai sieve with a fine mesh to get rid of dust:-

http://www.ebay.co.uk/sch/i.html?_odkw= ... e&_sacat=0" onclick="window.open(this.href);return false;

Pumice however is harder to get in the UK and pretty expensive.

[Steve Johnson]

I totally agree with Kristian and Dave about trying to reuse runoff for watering -- don't do it.

Benny -- It's highly recommended that forum members include basic location and climate info in their profiles. Then whenever they ask for advice, respondents are more likely to produce useful answers. See the following screenshots:



Here's my profile as an example:



If you live in the US, you can reference the USDA Plant Hardiness Zone Map for your profile:

http://planthardiness.ars.usda.gov/PHZMWeb/" onclick="window.open(this.href);return false;