CoronaCactus wrote:You could substitute the pumice for crushed granite #5, which is about the same size chuncks as pumice, it's cheaper too. The rest of the mix would be for water retention. Personally, i'd chose one or the other. I've used both but see no reason to anymore.
Substitute the sand for DG (the sandy, finer stuff, not too chunky) this definetely adds weight to the pots. A flat of DG/pumice pots is twice to 3 times the weight of a pumice/supersoil flat. DG has pretty much all the trace elements needed, which in turn allows you to be less picky about which fertilizer to use.
BTW, if you're a CSSA member or a member of a local SoCal affilliate club, the HBG Desert Forum is held each year in January and admission is free.
Well, I do like the idea of DG. The closest source I can find in my area is Bourget Bros. in Santa Monica, but they only have it in 60 lb. bags. The small size of my collection keeps me to more limited amounts of what I can handle, so I'll look around to see if I may be able to find a place that has the finer grade of DG you're talking about. If that doesn't work out, #5 gravel might be more doable.
The CCC's cactus mix doesn't have all that much pumice, so I think the pumice I was planning to add would be substituted for #5 gravel just fine. After finally settling on the custom mix that seems the best fit for me, I'm finding these ratios: 60/40 pumice to CCC cactus mix for most of my cacti, 70/30 pumice to cactus mix for the Astrophytums, Turbs, C. senilis, and Melo matanzus. If I use the #5 gravel instead (yes, I'd rather have that stability!), I think that I may need to skew the ratio a little in favor of the cactus mix. Maybe more like 50/50 and 60/40, since gravel does lose the porosity one would have with pumice. That being the case, I'd appreciate any ideas you have. I understand there's no way that someone else can ask me for any kind of precision. However, I'm glad for whatever advice that comes from the people who are willing to give it.
EDIT -- I just found DG at La Canada Rustic Stone in Pasadena. They sell finer grades, and by the shovelful is no problem, so a 20 lb bag would suit me just fine. (Oddly enough, now I know that #5 gravel is the thing I can't find anywhere.) This changes the equation, since I'll have to figure out the proper balance between DG and pumice. On the one hand, too much DG will (I think) turn it into concrete, and on the other too much pumice won't let water hold long enough for the roots to get any moisture. Also, I've been using terra cotta pots. If my soil is DG and pumice, I'm concerned that in summer the pots would dry out long before my cacti have the chance for getting any moisture at all. Our summer heat is generally low 80s during the day, but with the occasional heat wave. Our part of L.A. is normally a good 5-10 degrees cooler than downtown or the San Gabriel/San Fernando valleys. Please bear in mind that I water only in the evenings. Under a worst-case scenario, I'm sure moisture would be retained over at least a night in terra cotta. Is that sufficient for the moisture needs of cacti, or would plastic pots be better?
Now I'm excited by the possibility of DG, especially being away from any organic materials. I'd really appreciate any help on advice for what is now "unknown territory" on my part.
By the way, there's a c&s society in the San Fernando valley that meets once a month on Sundays. Used to be a member back in the early 70s, so I think it would be great to rekindle the enjoyment I had with that when I was a lad. If I can make it, what a nice way to start 2012!
Thanks so much, Darryl. And merry Christmas to everyone on the forum!