Blue Cactus. Best guess?

[Stan]

I saw this today. I wish I could say its all next to an Aloe dichotoma..but,nah,its a tree.

[mcvansoest]

Best guess: Pilosocereus pachycladus.

[Stan]

Sounds good. Due to go to the gallery now.

[Viegener]

I agree. From what I see, most of the really blue cacti out there are P. pachycladus or P. lanuginosus, which is woollier. Geoff has some nice pics on here under Pilosocereus lanuginosus.

Two things though: many of these species come in a range from green to blue and of course the blue ones are the ones people love most & therefore reproduce the most (like the archetypal agave, A. americana, in its very blue version). Here's an example of a green P. lanuginosus from this year's Huntington ISI plants. Also the wool or down on lanuginosus often disappears on older stems, or is barely visible even on newer stems. Wooliness in cacti seems mostly associated with climate: they come from places where often the most reliable form of moisture is fog, often coastal fog.

Also, on all the specimens I've seen (and on most of the pics I've seen), the older stems become more green. Apparently people often start new plants to keep them blue (I'm pretty sure I read that from Geoff Stein). I suppose that means that the big all-blue plants you see sometimes are actually pretty young and pumped up on water & fertilizers.

[mcvansoest]

I have started trying to grow more of these as they seem incredibly well equipped to deal with the summer sun here. The only big specimen I have is a P. pachycladus. It gets all day full sun and I probably could water it less than I do.
Here the plant is on the white/grey side of blue and to me the greening of the stems occurs/starts in bands and then gets more pervasive as the stems gets older. However it is more apparent to me in the winter than in the summer (I am going to go outside and have a look at the plant next just to see if that is really true. The strange looking section on the left bottom stem is from when it was rooting - it grew a bit but not in its normal shape. The branching at the tip of that stem happened after that tip froze... one night of inattentiveness and not covering it was enough. So now they get their tips covered if there is even a minor chance of frost.
It took a while to start flowering but since it has started it has been pretty profuse. Not very much wool on this particular specimen, just a little bit here and there.

IMG_0416.jpg (108.75 KiB) Viewed 1053 times

[Stan]

Oh ,yeah,that's nice Mac. It needs to be a centerpiece to show that off. You might get higher blue levels all year in warm winter Arizona. I have seen photos of these in Brazil and they held blue to 20' or more and in huge plantings. Someplace on the internet. Geoff's in soucal were thriving. Several species.
On the other hand..no doubt with slow poke growth,or wrong soils or mix..they will stay green..green- yellow is even worse. Once they get THAT color..even better care wont bring the blue back is what I've had happen. But,like Vieg said- those rescued poor soul cactus will send out blue arms with good care.

[Viegener]

Geoff's pics are some of the nicest ones to be found online. Mine are all still less than 2' (60cm) tall, but they're not really slow growing. They get good light, very well-draining soil & ample water in summer. I don't put extra fertilizer in them, but the mix I have is good organic soil with more than ⅓ perlite or pumice.

[mcvansoest]

I have never fertilized mine. It is in a big plastic pot, but I am pretty certain it has grown roots out of the bottom... I have been meaning to plant into the ground proper for a few years now, but since it has been doing so well I have just left it alone.

I have a lanuginosus in the ground, but I forgot to cover it two winters ago on the one freeze night we got... it is still recovering from that... two of the 3 stems that were in the original pot are done for and the third only started on a branch this spring... I have 2 NOIDs that I got in small pots at a BBS and I have pilosocereus pentaedrophorus which I think was part of the same ISI release as P. magnificus. That one is growing but looking like it wants more light under the 50% shade cloth it is under...