In the fall of 2011 I was gifted with a foot long cactus cutting. I know nothing about cacti. I tried to pot it in some sandy soil (it was rich soil TM) and it rotted out the bottom on me. I cut out all the rot and mush and it healed over again. I place it out doors in the sun over spring and the tip is growing. I've kept the base wrapped and out of sunlight and it has little pokey root tips coming out. Who's the Cactus expert here? Dale?
I've got a bunch of that bluff sand now. Thats pretty much pure sand. I know many deserts are Alkaline. It sure TASTES alkaline. Do cactus like alkaline soils? Could I mix up a cactus mix with some sand and a little ash? So many questions. I don't want to kill my cactus. They're amazingly tough little buggers - I'd never believe how tough except I've been watching the thing. Somebody please help!
I'm going to just talk generalities, and yes, cactus do well in alkaline soil, as most desert soils are. That said, there are still mineral accumulations found in the desert (salt, gypsum, borax, etc.) that can get a little too concentrated and the cacti cannot survive. What you did by cutting it and letting it heal over was good. Many cacti can propagate from cuttings, but they have to have a healed over scar so that they do not lose water through it, nor pick up diseases while it is open.
I've grown cholla cactus on pure sand. No amendments, no organic matter, no ash, no nothing. And it rooted, just like you have observed.
Great. What would you suggest as a planting depth? Should they be watered in or is nearly dry sand best?
Edit: Like I said - I don't know anything about Cacti, including the type. It's an upright and ridged only slightly prickly kind, and otherwise seems like a pretty standard cactus - just like you'd see in the movies. I don't think its a saguaro and its not a flat prickly pear type or a little low to the ground button type
Planting depth is unimportant. Cacti that root from a cutting understand where they are in the soil and will adapt. They sense where the soil is and send roots out into it, and they grow up from whatever side is oriented to the top. If you lay it flat, roots will grow out the bottom and new segments up at the top.
How much you water it will determine how fast it grows. Cacti have adapted to growing when water is available and going into stasis when it isn't. Which means you really have to let the soil dry out bone dry between waterings. If you give it a good soaking once every two or three weeks, that would be a good watering schedule to get maximum growth. I did that with my aloe plants when I lived in Las Vegas, and after two years they were HUGE.
If cacti go into a prolonged, months long drought, they can shrivel as they slowly lose stored water, but after a soaking, they will plump back up to their normal size and maybe leaf out and flower. They also make the most of whatever soil nutrients are available. Often the only nitrogen they get is when a passing coyote takes a leak within a few feet or a lizard burrows under them and dies. If you mulch it with dried bugs swept up from behind the refrigerator, that's probably enough organic matter to be adding. The chitin in the bug's exoskeleton will break down ever so slowly, with the infrequent waterings, and that will be enough to keep the cactus happy.
If you are interested in identifying what type it is, this Wiki page has a lot of pictures and you can maybe narrow it down.
Just so you know you're not crazy trying to grow cactus in the PNW, I have had a patch for years. I planted them on a bed of gravel over my clayish soil. They are doing fine. They flower each year and I harvest the pads to eat. They are shown to be anti-diabetic. I cut them and put them in my sauerkraut. How's that for a cross cultural experience? They fruited last year, but the winter was harsh and the fruit shriveled and died before ripening. I wouldn't count on fruit, but you should be able to grow some types of cactus outside, as long as you let it heal before planting, like John said, and you have very fast draining soil.