Expert: Sarracenia Northwest - 3/15/2010

Question
Hi, a couple weeks ago I planted up some venus flytrap, Sarracenia flava and minor, warm temperate pings and a cape sundew in separate pots using a 50/50 peat sand mix. I used a new bag of sand that said it was washed and could be used in potting mixes. I also washed it pretty thoroughly before mixing the soil, but soon after potting them up I started seeing what looked like mineral deposits on the surface of the soil, and it seems to have only happened in the pots that I used the sand in. I then tested the water in the plant trays, my source water, and water that had been used to wash the sand with cheap water testing strips. it seems that the sand is the culprit, as the wash water had about 100 ppm dissolved solids and the water in the plant trays now is at about 150-200 ppm dissolved solids. I bought some perlite and was ready to re-pot them using the perlite but I just wanted to make sure I wasn't freaking out as my source water is reverse osmosis (I tested it also and it is fine). Is it normal to have minerals that come along with the sand which aren't harmful to CP's, or did I just buy the wrong type of sand and need to re-pot them immediately? The actual plants are just starting to come out of dormancy and there is no sign of damage yet. I don't have any other questions, just the one about the sand... Maybe I'll just stick to perlite after this experience.
Thanks a lot
Richard

Answer
Hi Richard,

You didn't mention where you live.  I was curious since rock and soil products are often locally produced.

What it sounds like is your sand has some limestone or marble in it.  Washing it with the pure R.O. water leaches out the calcium.  I'm guessing that if you did a pH test it would come out alkaline.

Your experience is one of the reasons we don't recommend sand typically in potting mix for cp because it is so hard to predict what is going to be in the sand.  Here in Oregon one time I bought some sand that was dredged up from our Willamette river which goes right through the the most industrialized parts of the state.  It had a strange chemical smell.  Needless to say I didn't use it.  Sometimes you'll see threads on forums talking about sand and many people will buy sandblasting sand which is pure silica.  Good stuff, but expensive.  That is why we recommend perlite as an agent to lighten soil.  It's not that perlite is better, it is just more predictable, and fairly easy to find across the country.  Here in the Northwest we often use volcanic pumice since it's cheap and abundant with all of our volcanic terrain.  Pumice is not available in most of the east and midwest, however.

I do recommend repotting your plants.  With the TDS coming out so high from the wash water, and mineral deposits developing so quickly on the pots, it is just asking for problems.

Good Growing!

Jeff Dallas
Sarracenia Northwest
http://www.cobraplant.com