CactiGuide.com

The_Nikon_Guy wrote: ↑Mon May 18, 2020 12:50 am

I can categorically state that the cacti have grown WAY better in pure sand than in any other medium. I am absolutely convinced beyond any doubt that pure sand is the way to grow cacti.

This is inappropriate advice for most people. In the vast majority of climates around the world all cactus species would perish in pure sand. Substrate composition must vary and should always be based upon environment, practices, container, and the individual plants. There is no single "the" way to do anything.

Aloinopsis wrote: ↑Mon May 18, 2020 12:45 pm

The_Nikon_Guy wrote: ↑Mon May 18, 2020 12:50 am

I can categorically state that the cacti have grown WAY better in pure sand than in any other medium. I am absolutely convinced beyond any doubt that pure sand is the way to grow cacti.

This is inappropriate advice for most people. In the vast majority of climates around the world all cactus species would perish in pure sand. Substrate composition must vary and should always be based upon environment, practices, container, and the individual plants. There is no single "the" way to do anything.

Quite right - most inexperienced people would probably end up killing their cacti if they didnt follow a strict watering regime etc..I've had close to 3 years to learn that.

Having said that, I would like to correct your statement - hobbyists tend to grow cacti in pots under more controlled conditions - this would prevent a lot of perishing in home gardens.

Maybe I should have said "based on my personal experiences, pure sand is a very viable way of growing a large number of cacti" - this statement fits more with what I am doing and currently experienceing.

I do grow cacti in gritty, rocky soils and they do well - just not as good as when in pure sand.

Back to what a friend of mine said "you can grow cacti in anything if you get the watering right". Meaning rot through the soil staying wet too long is the major danger for growers. However PH of the potting soil also can matter as most S. American cacti prefer a soil slightly on the acid side of neutral. However added to that with a solely mineral substrate like sand you need to fertilise since there is no organic material to provide the feed the plants require.

some stuff I found on the internet. AWC is available water capacity WRC is Water retention characteristics. Who knew crushed bricks held so much water ? And lava holds water like sand which is not much. https://www.tandfonline.com/doi/full/10 ... 18.1447293

Porlith has a high AWC of 0.38 m3m−3, which is in a comparable magnitude with the one for bricks (up to 0.4 m3m−3; Blume and Runge 1978; Nehls et al. 2013). These comparable water retention characteristics can be attributed to similarities of the structure of these two materials.

For tuff, the measured FC (0.23 m3m−3) exceeds the reported values of 0.10 m3m−3 (Da Silva et al. 1993) and 0.12 m3m−3 (Wallach et al. 1992). The tuff studied in this work has, accordingly, more pores able to retain water in the range of the AWC.

Expanded clay, expanded shale, and pumice have similarly low FC and AWC compared to tuff and porlith. The expanded clay has a ceramic cover, which is likely to disrupt the capillary continuum and thus hinders the uptake of water (see the structure of the material in Fig. 2). Expanded shale shows a low and narrow amount of pores retaining water in between pF 1.8 and pF 3.0, draining almost completely at pF > 3.0.

Regarding pumice, previous research on its porosity shows that it has a wide pore size spectrum and that shape and connectivity of the pores depends on the origin of the pumice (Whitham and Sparks 1986; Lura et al. 2004). Gunnlaugsson and Adalsteinsson (1994) report that the majority of pumice is composed by closed, occluded, or dead-end pores not available for water storage. This particular porosity may also be present in our studied material, and it can be reflected in the high variance of the WRC (Fig. 2) at pF ≤ 2.5 (SD = 0.007 m3m−3), and pF 3.0, with a SD = 0.053 m3m−3. For higher suctions (pF > 4.0), the values are more consistent as the materials were crushed prior measurement.

Lava has a very low AWC. Its water retention characteristics are quite similar to the ones of the sand of our study. The low AWC is mainly attributed to its large pore sizes >50 μm, some of them clearly visible, as depicted in Fig. 2.

The_Nikon_Guy wrote: ↑Mon May 18, 2020 11:07 pm

I do grow cacti in gritty, rocky soils and they do well - just not as good as when in pure sand.

Theoretically you could grow in pure sand if you 1/ adjusted the particle sizes so you get the right water retention for the species. (fine sand can stay wet for days and course sand can dry out in minutes) and 2/ if you had a very good fertilizer program. So it becomes hydroponics basically. There is quite a high margin of error if you don't know what your doing though.

I'm wondering if anybody has ever seen you and The Nikon Guy in the same room.