Probably overwatering, or, more likely, inappropriate soil. There is nothing wrong with watering most cacti until the pot is full (I do that every time I water mine), but the compost must be porous. If it holds too much water, the plant is likely to rot.

I agree with improper soil, but if it is a dogtail cactus, Selenecereus testudo, you should be watering more often than once a month. I water mine weekly or at the least every other week.

You say Selenicereus, I say Deamia.

TJ and Mentha are correct - this should be treated as a tropical cactus, but it doesn't want water-logged soil, so increase the porosity and Dogtail will be happier. The watering regimen can then be increased to 2-4x a month, which is important because this wants to grow Spring-Fall, and mabe Winter too if it's warm and sunny enough.

And one more thing - when you do get flowers, be prepared to be awed - it's got one of the largest ones.

Jeff,
The last time I used Deamia, I got jumpped by the cactus police, so I decided to conform. ;) Can't please everyone I guess.

Rhonda,

I don't know who those people are, but we shan't have anything to do with them. If it was good enough for Mr. Borg, it's good enough for me.

Well, if it was good enough for Mr. Borg, it's good enough for me, too. Deamia 'tis.

R.

Rhonda,

An excellent suggestion - after all, we seek peaceful coexistence.

I also have this plant. I grow mine along with my Epi's and Rhipsalis.
Does anyone have a picture of the flower or the full grown plant?

Thanks

Sorry Jeff,
I seek world domination! Mwwwwaaaahhh! ;)

Not my pictures, but here are some flower pictures. They look like any other white night flowering jungle type cereus.

Here is a link that might be useful: flower pictures

Rhonda,

That's something I didn't know, so thanks for enhancing the knowledge.

You don't find them extraordinarily large (well, maybe just larger) than your normal tropical cactus?

BTW, I like Strophocactus even more than Deamia - what say we call it that?

Cryptocereus, Deamia, & Strophocactus, have all been lumped into Selenicereus. If Deamia is the oldest name then I'll stick with that. I've hardly ever heard of Strophocactus, and only in the reference to Aporocactus. Deamia and Aporocactus really have nothing in common IMO.

The flowers are just smaller than an E. oxy, which has fairly large blooms for an epi, but not as large as some of the hybrids.

Here is a link that might be useful: Interesting reading on the epi clan

That's not just your opinion, Rhonda, that's mine, too. To think that Aporocactus and Deamia have something in common enough to include them in the same genus is lumping gone mad.

Cryptocereus's passing must have been a secret (yuk).

Thanks for the info, but the link isn't working. Is it my computer again?

Hmmm, the link worked for me. It was just a compulation that Jim Hunter made of epiphytic cacti and where they've been on the genetic food chain. Not too interesting to those not really into epiphytic cacti and their nomenclature. If I had to lump them, I'd lump into four groups. I might even split the Rhipsalis group into two different classes, with two types each.

1. Holiday Cacti: Schlumbergera/Rhipsalidolpsis, (Not because of flower, but growth)
2. Spiney: Hylocereus, Selenicereus, Weberocereus, Aporocactus etc.
3. Epiphyllum, Disocactus, etc
4. Rhipsalis/Hatioria/Lepismeum etc.

http://gotepis.com/drupal/node/4

Thanks for breaking it down, Rhonda. The link works like a champ now.

Weberocereus but not Weberbauerocereus, eh?

Wow Jeff,
You're throwing new names at me right and left, keeps me on my toes. Is Weberbauerocereus a columnar cactus? From the pictures I found, it doesn't look like an epiphyte.

Milady R,

I'm just trying to keep up with you re the new names - you're making my head swim in the nomenclatural morass. I believe it is such a columnar. There was likely one W-cereus in proximity when I had the great fortune to visit Mr. J. Pickering (South American Cactus Grower Extraordinaire and bon vivant avec raconteur).

{{gwi:626555}}

Let's start a campaign to bring back Roseocactus, which is, I think you'd agree, a most euphonious name.

Wow, that's one happy group of cactus.
I euphorically agree, Roseocactus is an euphonious name.