FlytrapCare Carnivorous Plant Forums

Here's something interesting I came across when running some tests for an aquatic bog being built (using over 600 cubic yards of media!).

I was testing the pH/E.C. values for a 50/50 peat:sand mix, and a 50/25/25 peat:sand:compost mix.

When I used mason sand (a.k.a. pool sand, play sand, paving sand), I found it had an extremely high pH buffering capacity. This is BAD news for carnivorous plants. In peat, with a starting pH of 3.8, it managed to rise to 6.4 in the 50:50 mix!

With the compost mix, I was expecting the pH to rise as compost tends to draw the pH much higher (as it starts in the 8.0-8.4 range). The sand brought the pH to the same 6.4!

So, I substituted the sand in both mixes for what is known as 'low pH sand' (which ironically has a starting pH of 6.5). This yielded a 3.9 pH for the peat/sand mix, and a 6.3 for the peat/sand/compost mix. Much better! I believe the low pH sand is silica based - such that it has no buffering abilities.

So, consider this a warning for those using playground sand or similar!

Thanks for mentioning this issue, renesis. This is a very common and important problem and warning regarding carnivorous plant culture.

Many types of sand are not almost pure silica (silicon dioxide or quartz) but are instead composed of a lot of different types of rock and minerals, including limestone (very high pH) and other sedimentary rock, igneous, metamorphic and conglomerate rock, etc. The sand used by masons and for children's sandboxes looks to me like sieved riverbed or beach sand, composed of silica but also of all these other kinds of rock ground to little bits by the water. Many of the minerals in those other kinds of rock are water soluble and bad for carnivorous plannts.

Silica sand on the other hand, sand composed almost entirely of silicon dioxide, is inert and insoluble, perfect for carnivorous plants. Silica sand is normally found in large buried deposits and mined from them. It is usually very old sand, geologically.

One way to determine if the sand one has is silica sand or riverbed/ocean sand is to look at the grains with a magnifier. If there are many particles that are opaque and have large color or other differences, it is not silica sand. Silica sand will have grains that are almost all translucent and although the color varies somewhat between grains, they will generally be a light color instead of dark. Even silica sand will usually have some percentage of opaque or darkly colored grains, but that percentage is usually very small (to me it seems like less than 5 or perhaps 3 percent, in the silica sand I use).

Anyway, thanks for bringing up the issue. I have poisoned and killed a lot of Venus Flytraps by using the wrong sand. Riverbed sand and other surface sands are easy to find, but generally not good to use. (Although I do wonder what the sand looks like in the Venus Flytrap native territory.) Silica sand is a little harder to find, but it does have industrial uses and can be found here and there. The sand I use is "blasting sand," which is used by many trades for sandblasting.

Steve

I've been using playsand as a mix with success to all my VFT. Might depend on the brand and how you sanitize the sand.

hb

hackerberry wrote:I've been using playsand as a mix with success to all my VFT. Might depend on the brand and how you sanitize the sand. hb

Well, you may be right. I'm sure that I rinsed and agitated the play sand I used well, but I can't really remember. Also, results may depend upon the original source of the play sand or mason's sand. Some surface sand deposits (like riverbanks) may have a purer silica content than others.

Although soaking and rinsing the sand very well may eliminate most of the dried soluble residue, it seems to me that the acidity of sphagnum peat moss and water would continue to dissolve the other-than-silica rock grains in the sand and add those detrimental minerals to the growing mix.

Just out of curiosity hb, have you looked at your play sand under high magnification? If so, about what percentage does it have of translucent grains compared to opaque?

Steve

I've used sand that was packaged for growing cacti and it worked well.

Hi Steve,

Over 70% of the translucent grains. Plus I strain it to lose the finer sand.

hb

You could also just avoid sand and use the Standard CP mix of 1:1 Peat-Perlite ofcourse