The Short Life And Gruesome Death of Mammillaria candida

[zpeckler]

Well, I think the title tells most of the tale.... I had two Mammillaria/Mammilloydia candida, one that I bought last spring and one I bought this spring. As a little background on my growing conditions, I had them both planted in pure Turface MVP, and was watering them weekly after the mix dried out. Since they're in a pure mineral mix they got MikeInOz/Steve Johnson's fertilizer protocol with every watering. I live in Northern California outside Chico in the Sacramento Valley, and the climate here is definitely Mediterranean, with very hot, dry summers and cool, moist, rainy winters. Average temps in summer are consistently in the 90's, frequently in the 100's, and rarely in the 110's. Winter temps never get below freezing, and rarely even into the 30's. 

Basically, both plants succumbed to rapid, overwhelming rot. One sec they seemed fine and the next completely caved in and collapsed over a gooey rotten core. As a post-mortem I unpotted the corpses and it was the plant themselves that rotted. They both had great looking root systems.

I don't know what killed them, but considering both my plants from this species died within a week of each other I'm suspicious that it was something I was doing wrong. The plants were bought from two different nurseries, so it's not like I got them from a bad grower. They were even kept on opposite sides of my cactus shelf with no other plants around them showing any sign of distress/disease after a thorough inspection.

Anyone have any advice about how to take care of this plant more successfully next time? The cultivation advice in my cactus books is rather limited, consisting mostly of "they're rot-prone, grow them in an extra-fast draining mix." I take what Llife says with a grain of salt, but they did have one specific bit of cultivation notes that I'm wondering about:

"During the growing season enrich the soil using a fertilizer rich in potassium and phosphorous, but poor in nitrogen, because this chemical element doesn’t help the development of succulent plants, making them too soft and full of water."

Any thoughts on the veracity of this claim? It goes against a lot of what I've learned here on the forums regarding cactus nutrition, but each species is different.

Any other bits of advice from growers who have successfully taken care of this species?

Roots for days... This is the one I got a year and a half ago.

M candida roots 2.jpg (273.71 KiB) Viewed 4429 times

DOA. I just got this one from Mesa Garden a few months ago in March.

M candida rot.jpg (223.62 KiB) Viewed 4429 times

[Steve Johnson]

I take what Llife says with a grain of salt, but they did have one specific bit of cultivation notes that I'm wondering about:

"During the growing season enrich the soil using a fertilizer rich in potassium and phosphorous, but poor in nitrogen, because this chemical element doesn’t help the development of succulent plants, making them too soft and full of water."

Any thoughts on the veracity of this claim? It goes against a lot of what I've learned here on the forums regarding cactus nutrition, but each species is different.

Complete myth, and the reason why we shouldn't be taking cultivation advice from Llifle on the matter of fertilizers. MikeInOz will be the first one to tell you why Llifle's recommendation is so wrong. By the way, all species are the same when it comes to their nutrient requirements.

Based on my limited experience, the only thing that rots cacti in summer is if the overnight lows are above the 75-80F range. That's when they go into dormancy -- fat, happy, and asleep. Definitely a problem in places like Arizona, although I don't know if your overnights would be high enough to qualify for a summer dormancy situation. If not, I haven't a clue about what happened. Wish I could be more helpful.

[Tom in Tucson]

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

Mammillaria candida has a huge growing range with at least 3 forms (or varieties) . The form west of Parras, Coahuila (Tanque Menchaca) gets around 4" of rain per year. That form can be as touchy to water as it's neighbors, like Rapicactus mandragora , Mammillaria lenta, or Astrophytum coahuilense. The forms from further east (like SlP) should be more tolerant of "incessant" fertilizer.

[zpeckler]

Complete myth, and the reason why we shouldn't be taking cultivation advice from Llifle on the matter of fertilizers. MikeInOz will be the first one to tell you why Llifle's recommendation is so wrong. By the way, all species are the same when it comes to their nutrient requirements.

Good to know. Not having to worry about different nutrient requirements for different species eliminates a huge variable.

Based on my limited experience, the only thing that rots cacti in summer is if the overnight lows are above the 75-80F range. That's when they go into dormancy -- fat, happy, and asleep. Definitely a problem in places like Arizona, although I don't know if your overnights would be high enough to qualify for a summer dormancy situation.

You know, heat dormancy is something I've been thinking about for some of my cacti. We haven't had a heatwave in a bit and daytime temps have been steadily at their average in the high 90s. Minimum night temps just before dawn are usually in the high 60s but frequently in the low 70s. The vast majority of my cacti are growing, but there are a few that seem to have stopped for the season. I think the candidas were in that group, actually. It was tough to tell if there was new growth because of the dense spines on top. It's it inadvisable to water cacti during heat dormancy?

Mammillaria candida has a huge growing range with at least 3 forms (or varieties) . The form west of Parras, Coahuila (Tanque Menchaca) gets around 4" of rain per year. That form can be as touchy to water as it's neighbors, like Rapicactus mandragora , Mammillaria lenta, or Astrophytum coahuilense. The forms from further east (like SlP) should be more tolerant of "incessant" fertilizer.

Thanks Tom. Habitat details are really helpful. 4" of rain is hella arid. Twice as much as Death Valley, but half as much as Phoenix or looks like. When I try again with this species I should probably space out the waterings a bit more.

[Steve Johnson]

Good to know. Not having to worry about different nutrient requirements for different species eliminates a huge variable.

Yes, and MikeInOz has been a great myth-buster on fert-related issues.

You know, heat dormancy is something I've been thinking about for some of my cacti. We haven't had a heatwave in a bit and daytime temps have been steadily at their average in the high 90s. Minimum night temps just before dawn are usually in the high 60s but frequently in the low 70s. The vast majority of my cacti are growing, but there are a few that seem to have stopped for the season. I think the candidas were in that group, actually. It was tough to tell if there was new growth because of the dense spines on top. It's it inadvisable to water cacti during heat dormancy?

Tom in Tucson's answer:

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

Generally true, although we have to beware of "outliers" in California. Here's an example from the summer of 2020, and you'll find all the details here:

viewtopic.php?p=379037#p379037

What I didn't mention in the post was the fact that the daytime high of 114 came with an overnight low of 80 -- something I had never seen in my part of L.A. before. Lows in the upper 70s leading into and coming out of it, so I was smart enough to hold back on watering until the overnights went back down into the low 70s. The summer of 2019 was a pretty bad one too. Since I've seen it before, I figure it'll happen again.

When it comes to the weather and your cacti, the National Weather Service is your best friend:

https://forecast.weather.gov/MapClick.p ... =-121.6009

You can get even more local by typing in your zip code. I have my local NWS forecast up as my browser's default page, and I check it every day. If (or more likely when) I get another summertime "outlier" with overly warm nights, I'll be prepared and you can too if you keep an eye on your local forecast.

Summer dormancy in California is unusual (first time for me in 2020). The more important thing to be aware of is knowing the difference between spring-growing, summer-growing, and "opportunistic" species. For example, most of my Turbinicarpus are summer growers, but Turb valdezianus does most of its growing in spring. The plant takes a break in summer, then puts on a little more growth in fall. I've found that Copiapoas are opportunistic -- they'll grow when they feel like it, but I water mine every 2 weeks in spring and summer anyway. If your powers of observation are good, you'll be able to pick up on the different months when your cacti are growing. Wonderful to discover their mysterious ways, isn't it?

[Tom in Tucson]

Tom in Tucson's answer:

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

Generally true, although we have to beware of "outliers" in California. Here's an example from the summer of 2020, and you'll find all the details here:

viewtopic.php?p=379037#p379037

What I didn't mention in the post was the fact that the daytime high of 114 came with an overnight low of 80 -- something I had never seen in my part of L.A. before. Lows in the upper 70s leading into and coming out of it, so I was smart enough to hold back on watering until the overnights went back down into the low 70s. The summer of 2019 was a pretty bad one too. Since I've seen it before, I figure it'll happen again.

I checked what was said in the link you provided. Thanks for pointing out that the overnight low temps. aren't mentioned.

It should be mentioned that the Mammillaria you show undergoing a horrible amount of stress that is approaching a fatal level grows typically at one of the highest altitudes of any in the genus, it's not totally surprising. OTOH, the species in question can and does regularly tolerate both high day and night temps. I monitor several weather stations daily. Check out this example of a weather station near the town I mentioned earlier: https://www.wunderground.com/dashboard/pws/ITORRE292

The reasons Iv'e gone to this length of explanation is twofold: 1) to ascertain what could be the source of the rot, and 2) to possibly help those who are dealing with a similar issue in the future (if anyone is searching this site for some answers to a similar problem).

[MikeInOz]

I have found candida particularly susceptible to rotting compared to a lot of other Mamms. I now give them an extra coarse mix and add limestone ''sand'' as well. Also, you should be careful about having your plant set low in the pot (mine are always right up near the top of the pot) and then surrounding it with stones which will hold humidity and impede air movement around the base.

[jerrytheplater]

Also, you should be careful about having your plant set low in the pot (mine are always right up near the top of the pot) and then surrounding it with stones which will hold humidity and impede air movement around the base.

That is good advice for many plants. Thanks.

[madkactus]

For what it's worth. I think it's safe to say that your Mammillaria somehow, someway got and retained too much water. I've had cacti rot the exactaly same way. Sometimes it seems nothing you obviously did wrong. In my experience Mammillaria cactus seem "bullet proof". Be very carefull and sparce with the fertilizer.

[zpeckler]

Thanks for all the advice, everyone. I think them getting too much water may be the cause.

I'm getting really concerned that 100% Turface as a growing medium doesn't dry out as quickly as I thought it did. The smaller of the two candidas was the one that died more recently, and because I was busy all week with work I jut put the pot with the carcass off to the side to deal with later. 5 days later I just got around to dumping it out to clean out the pot, and the growing medium is still really damp! Granted, it's been in the shade this whole time and not in the sun to dry out like it would be normally, but it's enough to raise a significant level of concern.

In my growing conditions, I have to admit that I haven't been particularly worried about my cacti not drying out. I figured in 95F weather with 15% humidity that wouldn't be an issue. Now I'm not so sure!

I have the two pots that the candidas were in, which are roughly representative of the size of the pots that most of my cacti are in; all but the largest, anyway. I'll fill one back up with Turface and one with my usual growing medium and do a formal weigh test to see exactly how long it takes them to dry out after being "watered." After that I'll experiment with how much of a difference top dressing makes.

I guess I should be grateful to the sacrifice the candidas made. I'm trying to up my game and grow some much more difficult species (Echinocactus polycephalus, Mammilaria tetrancistra, Echinocactus paryii, Echinomastus johnsonii), and this alerted me to a potential serious issue.

[Steve Johnson]

I'm getting really concerned that 100% Turface as a growing medium doesn't dry out as quickly as I thought it did.

I'm kinda surprised by that, and you may want to run a test:

• Take 2 pots of equal volume, fill 1 all the way up with dry Turface and fill the other all the way up with dry pumice. For a more accurate test, weigh both with a digital scale and write down the weight.

• Saturate the Turface and pumice. When water stops coming out the drain hole, weigh the pots and write down their saturated weight.

• Weigh the pots every day until they go back to the dry weight, and make a note of how many days it took going from saturated to completely bone dry.

I'm thinking that Turface and pumice dry out at the same rate, but there's only one way to know -- test! If the pumice dries out more quickly, you may be onto something. Just to give you some insight here...

The humidity in my part of L.A. (the Baldwin Hills area to be more precise) typically ranges from 50% to 75-85%. Straight pumice takes too long to dry out, so when I mix 40% granite gravel with 60% pumice, the granite acts as a "moderator". I ran wet/dry tests on my collection's representative pot sizes about 10 years ago -- and talk about surprising, these were the results:

• The pumice-granite gravel mix goes from wet to bone-dry in about 6-7 days, and this is the same in spring and summer.

• Wet/dry time is the same regardless of pot volume.

I don't know if you can extrapolate much from my experience, but it may give you 3 possibilities you can work with:

• If straight pumice dries out faster than Turface and it doesn't dry out too quickly for you, I think a 5-7 day wet/dry time would be acceptable in your local climate.

• If straight pumice dries out faster than Turface, but the pumice still takes too long to dry out, add a little granite gravel to the pumice.

• If straight pumice and Turface dry out at the same rate, you'll know that both materials take too long to dry out. At that point, it's your choice to go with either one and add more granite gravel as the "moderator" so the mix dries out in a timely manner.

Don't know if it helps you at all, but this is what my mineral mix looks like:

Pumice-DG_rinsed04242016_forum.jpg (201.76 KiB) Viewed 4251 times

When you try another Mammillaria candida, I'm sure you'll do much better next time. If I didn't help, at least Tom in Tucson and MikeInOz did.

[MrXeric]

Thanks for all the advice, everyone. I think them getting too much water may be the cause.

Yes, I think this is right. Turface MVP on its own has a too small average particle size, making it slower to drain as well as being more water retentive. Over 40% can be grain sizes smaller than 2mm, while only around 16% is grains larger than 3mm (about 1/8''). See the complete particle size analysis with exact numbers here: https://www.turface.com/sites/default/f ... 2.2017.pdf. I highly doubt the substrate was dry at the root zone within a week in your climate in a non-porous pot.

I don't have many years of experience growing M. candida, since I bought mine only 2 years ago from Mesa Garden ('caespitosa' SB 326 Saltillo, Coahuila), but it's been growing nicely in the time I've had it. I keep it in a standard porous terracotta 4in flower pot, with substrate around 85% mineral (mostly pumice that is 1/4''), I water every 2 to 3 weeks during the growing season and keep completely dry over the winter, and it gets direct sun for most of the day (>6h).

[keith]

'm getting really concerned that 100% Turface as a growing medium doesn't dry out as quickly as I thought it did. "

Yes i agree I don't use 100% turface or 100% pumice. I did once works great for about a year or two then it goes bad or something. I grow this species from seed it is rot prone but grows fast enough that nurseries often offer it for sale. I have tubercles die back on my older plants which is weird. I have two of them now and like most of my cactus always wary of over watering them . Maybe added Dolimite lime may help I think they grow out of limestone rock faces.

Mammillaria dehertinana a different species I have one left from seed that I keep chopping the top off and re rooting and getting clumps from the old bottom part. It flowers sporadically although long ago I had a great big clump which died in phoenix AZ too hot I guess ?

[Steve Johnson]

I keep it in a standard porous terracotta 4in flower pot...

See this:

viewtopic.php?t=45833

When you go there, be sure to scroll down and see my response to Steve-O, then see what greenknight said -- it'll give you a few further details.

[MrXeric]

I keep it in a standard porous terracotta 4in flower pot...

See this:

viewtopic.php?t=45833

When you go there, be sure to scroll down and see my response to Steve-O, then see what greenknight said -- it'll give you a few further details.

The first set of images look more like a substrate issue rather than a container issue. That soil looked like it went hydrophobic causing the water to flow towards the path of least resistance - the interface between the soil/roots and the pot walls.

Roots stick to terracotta because the root hairs "grab" onto the pores. This isn't an issue for the plant's health, just that it makes repotting more tedious than if the plant was in plastic. Broken fine roots are also a nonissue since they will die anyway from transplant shock. I trim and clean roots when repotting.

I use terracotta for pots 4in and larger, especially if they will be under direct sun exposure. Plastic gets hotter than terracotta and since plastic pots have thinner walls, the heat will more easily cook the roots against them. I closely pack any plastic pots that get direct sun to block exposure to the sides. The pots are in trays with sides that go up to around half the height of the sides, so the outer pots get some protection too.

I do agree that terracotta shouldn't be used as the primary means to get the substrate to dry out faster.