The Short Life And Gruesome Death of Mammillaria candida

[Steve Johnson]

I use terracotta for pots 4in and larger, especially if they will be under direct sun exposure.

I PM'd our go-to guy on horticultural matters (MikeInOz), and from his response, what you said makes perfect sense for growers who keep their cacti under direct sun. I still believe that roots grow better in nonporous pots, although it's just my impression, and I'll freely admit that I don't have any solid evidence to back up the claim. For whatever it's worth, Mike has been growing cacti for quite a few years (he used to be in the nursery trade), and finds that the roots of his plants look better in plastic. You can check out his Member Blogs thread to see his setup:

viewtopic.php?p=377464#p377464

Re. your pots 4" and larger, you might want to consider white glazed ceramic.

[zpeckler]

Well, an interim update. I've been doing some growing medium drying tests, and the prelim results have been illuminating. In order to minimize variables I set up two identical test pots: One with my usual growing medium of 50% Turface, 25% 3/8" pumice, and 25% potting soil and the other 100% Turface. I only have two free pots that match, and I didn't want to introduce additional variables by testing more samples at once in a mismatch of different pots. The pots are 4.5" wide by 3.75" deep, and made of high-fired glazed ceramic. Once the test with these two growing mediums are done, I'll do additional mediums. I started off with my usual mix and Turface--as opposed to Turface vs pumice as Steve suggested--because I wanted to get an idea of the characteristics of the actual mediums I have cacti in first. I filled both pots to the same depth; 1cm below the lid of the pot. I saturated both pots thoroughly by letting them sit in a tub in water the first morning for 10min, and then have been weighing them every morning since then.

So I have a week of data, and NEITHER mix is fully dried! The 100% Turface has been drying faster than my usual mix, but it still is retaining 28% of the water I initially soaked it with. My usual mix has 33%.

WOW. This was unexpected. This is a LOT slower drying than I ever thought was possible in my climate. While I figure this out I've stretched out the watering of my cacti to every two weeks.

More will be revealed. I'm gonna continue testing out more mediums. I also emailed John Trager at the Huntington Botanical Gardens with growing medium questions, but he hasn't gotten back to me yet.

[Tom in Tucson]

Well, an interim update. I've been doing some growing medium drying tests, and the prelim results have been illuminating. In order to minimize variables I set up two identical test pots: One with my usual growing medium of 50% Turface, 25% 3/8" pumice, and 25% potting soil and the other 100% Turface. I only have two free pots that match, and I didn't want to introduce additional variables by testing more samples at once in a mismatch of different pots. The pots are 4.5" wide by 3.75" deep, and made of high-fired glazed ceramic. Once the test with these two growing mediums are done, I'll do additional mediums. I started off with my usual mix and Turface--as opposed to Turface vs pumice as Steve suggested--because I wanted to get an idea of the characteristics of the actual mediums I have cacti in first. I filled both pots to the same depth; 1cm below the lid of the pot. I saturated both pots thoroughly by letting them sit in a tub in water the first morning for 10min, and then have been weighing them every morning since then.

So I have a week of data, and NEITHER mix is fully dried! The 100% Turface has been drying faster than my usual mix, but it still is retaining 28% of the water I initially soaked it with. My usual mix has 33%.

WOW. This was unexpected. This is a LOT slower drying than I ever thought was possible in my climate. While I figure this out I've stretched out the watering of my cacti to every two weeks.

More will be revealed. I'm gonna continue testing out more mediums. I also emailed John Trager at the Huntington Botanical Gardens with growing medium questions, but he hasn't gotten back to me yet.

I use a huge variety of ingredients (some would say too many). A couple that I have used with a low absorbency (and consequently a quick drying rate) in the past with "difficult" species: haydite (heat-expanded shale or slate), and crushed (not powered) diatomaceous earth (DE, a common oil absorbent). Either mix with your favorite soil, or try both separately and, let me know your results.

[Steve Johnson]

Also, there's one variable you won't be able to account for -- cactus roots taking up the water. I got lucky when I nailed a 60% pumice/40% granite gravel mix for a wet-to-dry test with actual cacti in the pot. If your wet-to-dry test showed that 100% Turface dries out more quickly than 100% pumice, sounds like Turface will be the better way to go. Sorry that you may have to be guessing here, but I understand why you wouldn't want to put cacti at risk when you test different potting media. And hopefully John will be getting back to you soon -- I'm keenly interested in what he'll have to say.

[SDK1]

Particle size is king. Any amount of fine particles (potting mix) over about 15% is going to lead to the existence of a perched water table in the pot as well. Same goes for particles under ~1/8" in size. The "best" (most productive) potting mix is one where the particle size is uniform. Creates a uniform distribution of macropores in the mix. More space for the roots too.

Even all of the gritty mixes stay wet a lot longer than people think. At least longer than I always think. I'll go to repot something that hasn't been watered for 5-7 days in the middle of 90-100 degree temps and the mix is still pretty damp. Maybe I'm the odd one out for being surprised, I don't know.

Turface 100% stays wet too long to be watering those plants at that frequency. I've made the same mistake. Works real well for rooting cuttings or pups in my experience though, especially when you sift it to just get the fine grained stuff. Anyway, I wouldn't even use 100% Turface with uniform particle sizes above 1/8". I'd probably do Turface plus crushed granite. But at that point it's only one ingredient, pine bark, away from my normal mix.

[MrXeric]

I use terracotta for pots 4in and larger, especially if they will be under direct sun exposure.

I PM'd our go-to guy on horticultural matters (MikeInOz), and from his response, what you said makes perfect sense for growers who keep their cacti under direct sun. I still believe that roots grow better in nonporous pots, although it's just my impression, and I'll freely admit that I don't have any solid evidence to back up the claim. For whatever it's worth, Mike has been growing cacti for quite a few years (he used to be in the nursery trade), and finds that the roots of his plants look better in plastic. You can check out his Member Blogs thread to see his setup:

viewtopic.php?p=377464#p377464

Re. your pots 4" and larger, you might want to consider white glazed ceramic.

White glazed ceramic actually sounds like a good idea. The glaze may even help reflect some of the heat and I won't be needing to move them away from the sun on really hot days. I will be looking into those pots for when I repot my Pilosocereus pachycladus next year. It's starting to get tall and moving it around is becoming a chore!

[zpeckler]

White glazed ceramic actually sounds like a good idea. The glaze may even help reflect some of the heat and I won't be needing to move them away from the sun on really hot days. I will be looking into those pots for when I repot my Pilosocereus pachycladus next year. It's starting to get tall and moving it around is becoming a chore!

I do something like this, actually. I have a lot of my smaller cacti in white, or at least light-colored pots. I also strategically arrange the lightest ones to the south to shield the others. I stuck a thermometer in some pots and I forget the exact temps, but the high albedo puts seemed to cut the soil temp by about 5-10F.

[Steve Johnson]

Hope you don't mind if I hijack your thread, Zac.

My 2 ¢ worth: Almost any town west of the Sierra Nevada Mtns. has cool summer nights, so overnight lows aren't the cause.

Tom -- I should be watering my cacti tonight, although I'm not sure if it's a good idea. My part of L.A. will be experiencing daytime highs of around 100 tomorrow and Tuesday, and as far as heat waves go, this is nothing compared to the record-breaking heat waves in summer 2020. I'm more concerned about the overnight lows of 71 forecast for Monday/Tuesday and Tuesday/Wednesday (RH topping out around 80%). If the lows turn out to be more like 74-75, do you think I'll be fine watering tonight, or should I wait until the lows go back down to the 60s starting Wednesday night? I'm inclined toward following the "when in doubt, don't" rule here, but I don't want to be paranoid about it either.

[Tom in Tucson]

Hope you don't mind if I hijack your thread, Zac.

My 2 ¢ worth: Almost any town west of the Sierra Nevada Mtns. has cool summer nights, so overnight lows aren't the cause.

Tom -- I should be watering my cacti tonight, although I'm not sure if it's a good idea. My part of L.A. will be experiencing daytime highs of around 100 tomorrow and Tuesday, and as far as heat waves go, this is nothing compared to the record-breaking heat waves in summer 2020. I'm more concerned about the overnight lows of 71 forecast for Monday/Tuesday and Tuesday/Wednesday (RH topping out around 80%). If the lows turn out to be more like 74-75, do you think I'll be fine watering tonight, or should I wait until the lows go back down to the 60s starting Wednesday night? I'm inclined toward following the "when in doubt, don't" rule here, but I don't want to be paranoid about it either.

Perhaps I should have been more accurate in also stating that particularity in last Summer, and early Fall, Diablo and Santa Ana winds can cause overnight low temps. to far exceed the usual nighttime averages, but these temps. are definitely the exception (rather than the rule).

Almost all succulent plants have a CAM range that fall within an upper limit less than 75˚-80˚ F. So, assuming some freak conditions don't occur, (climate change) it should be safe for you to water almost any Summer/Fall growing succulent plant.

[Steve Johnson]

Almost all succulent plants have a CAM range that fall within an upper limit less than 75˚-80˚ F. So, assuming some freak conditions don't occur, (climate change) it should be safe for you to water almost any Summer/Fall growing succulent plant.

Okay, so watering tonight then! Thanks, Tom!