I just made up a mineral mix with ~6% washed fine sand (~ 0.1 - 2 mm), then I remembered reading people saying fine sand was death to cacti (migrates to bottom of pot, where it holds water and impedes drainage and aeration). I was wondering whether those here actually had any first-hand experience with this and could confirm or deny these reports? And whether 6% in an otherwise gravely mix would be likely to cause any issues? (seems most reports imply much higher concentrations)
For reference: I put the mix through 60 soak/drain cycles to simulate about 5 years worth of waterings, finding only a slight build-up (concentration increased from ~6% to ~20-30%) of sand and fines at the bottom (about 3-4mm thick), however it was still mostly gravel and the pots drainage time didn't seem to change from first to last watering. I am putting the pots through a drying test now.
Depends what proportion of the mix it represents. I would not have thought 6% would make much difference. After all if you use soil/loam based mixes the soi/loam itself is composed of many particles as fine as sand and usually a considerable amount of sand grains anyway:-
"Loam is soil composed mostly of sand and silt, and a smaller amount of clay (about 40%-40%-20% concentration respectively."
It really depends how quickly the mixture drains for our plants. Provided when you water any surface water on the top of the pot disappears within a minute or so it should be OK. As to clogging the bottom of the pot, I would have thought the fine particles would get washed out of the drainage holes anyway?
Yeah well that's it, exactly what I thought before putting the sand in, but then I whipped myself into a fit of [probably irrational] fear when I began researching more, I came across all these ominous reports of cacti and death ... I think the main reported problem was an apparent affinity for fine sand to hold considerable water through surface tension, which is especially bad if there's spots of concentrated sand, such as at the bottom of the pot. My mix drains super quick, around 5-10 seconds I'd say, and I line the bottom of pots with one layer of newspaper which I poke holes in as my mixes are very heavy (mostly various gravels) and prone to eroding out from the bottom.
If anyone has some first hand experience I'd love to hear it!
I did have that experience when I 1st started, but I was using @ 1/3 of cactus mixture as "leveler's" sand -- which is another name for what you have. It's not "beach" sand, but there's a lot of fine stuff in it. Silver-lining on a "bad" experience -- We had an unusual prolonged dry stretch 3 Summers ago, & 1 nice (I'm guessing) a raccoon came up on porch & dumped @ 20 plants, many of which I had just repotted the day before, looking for grubs?? Anyway ran across several that had not been repotted that contained my original mix & yes, the sand was all caked @ the bottom & yes, it was far moister than some of the later "soils" I had progressed to. Those plants had been "slower" growers & yet they shouldn't have been -- based on endless readings on CF! Now I don't used ANY sands -- work primarily with NAPA 8822, Turface, & 2 - 3 mm (granite) poultry grit mixed with @20% quality potting soil. (We don't have access to pumice @ a reasonable $$)
Once bitten by the cactus collecting/growing bug, there is no known cure!
There's no 12 step programme for Cactaholics...so I shall just have to get some more!!
hoteidoc wrote:I did have that experience when I 1st started, but I was using @ 1/3 of cactus mixture as "leveler's" sand -- which is another name for what you have. It's not "beach" sand, but there's a lot of fine stuff in it. Silver-lining on a "bad" experience -- We had an unusual prolonged dry stretch 3 Summers ago, & 1 nice (I'm guessing) a raccoon came up on porch & dumped @ 20 plants, many of which I had just repotted the day before, looking for grubs?? Anyway ran across several that had not been repotted that contained my original mix & yes, the sand was all caked @ the bottom & yes, it was far moister than some of the later "soils" I had progressed to. Those plants had been "slower" growers & yet they shouldn't have been -- based on endless readings on CF! Now I don't used ANY sands -- work primarily with NAPA 8822, Turface, & 2 - 3 mm (granite) poultry grit mixed with @20% quality potting soil. (We don't have access to pumice @ a reasonable $$)
Good catch there, and I couldn't agree more. Animo, the buildup of the sand you described in the results of your experiment isn't slight. While I do give you credit for designing it as well as possible, there's no substitute for knowing how well the roots of your cacti will interact with the mix over time. The signs of trouble to watch out for are 1. difficulty in proper establishing, 2. subnormal growth rates (depends on how well you know the species involved), and 3. little or no flowering among the cacti you have that are mature enough to bloom. If you try going with the sand you have in mind for your mix, you may not like what you see in a year or two.
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Ah so glad I posted here, I think I was more or less in a state of denial as I'd spent so long potting the cacti up! Thanks for snapping me out of it
I think I will keep the cacti in the mix for a few watering cycles/months while I sift out the fines from the remaining mix to re-pot them back into, and add some extra nutritional rock and mineral types too.
The problem with removing the fines if you want to do so is finding a sieve (or riddle as it is often called in the UK) fine enough otherwise you loose half your mix. You need one designed for either sieving baking flour, or I find a piece of the fine mesh sold for fly screens many DIY stores sell is suitable. You will probably find there is no need to sieve out your 6% of sand though as it will have a negligible effect on drainage as Dan says.
Had a few days off and I ended up doing just that Dave also bought a 6mm garden sieve, spent the afternoon sieving the mix to remove anything below ca. 1 mm and anything above 6 mm. Then spent a couple days crushing and re-sieving the large remnants (I had >100 L of mix to process). Turns out about 1/4 of the mix was actually smaller than 1 mm (probably from the unsorted river sand I added) if I had of watered the plants and not completely re-done the mix, I think I'd have had suffered massive casualties. Feel really good about the mix now, I'll take some pics of my collection in the next few days and post them in the 'raised from seed' sub-forum if y'all interested
Better to recover from denial sooner than later! There were several things about cultivation & growing from seed that took a couple of years before the hard reality was in front of me. Trusting that the vast majority of people -- adjusting for individual geographic circumstances -- on CF know what the heck they're talking about can definitely save time with our learning curve!
Once bitten by the cactus collecting/growing bug, there is no known cure!
There's no 12 step programme for Cactaholics...so I shall just have to get some more!!
There were several things about cultivation & growing from seed that took a couple of years before the hard reality was in front of me. Trusting that the vast majority of people -- adjusting for individual geographic circumstances -- on CF know what the heck they're talking about can definitely save time with our learning curve! 