If you are in a temperate area:
Put it in a pot of cactus soil and water it quite a bit when you first plant it, but not too much that the soil will stay soggy for more than a few hours. Water it every 3-4 days.
It doesn't really go dormant in the fall/winter... it just won't grow as much without as much natural light as it would get in the spring/summer months.
It's actually good that you're going to be starting it about now, because by next spring, it will have a well developed root system.
When the frost is definitely done, keep it outside but in an area where it will get some shade and be protected from rain. An overhang from the roof on your deck is perfect.
Just leave it outside and water it just a little about once a week for as long as it's not getting below 50 degrees at night. I generally put my cacti out the last week of April and put them back in the second week of September.
As soon as it's not going to fall below 50 degrees in the night, they'll be fine outside... just don't keep them in direct sun. I have no idea why, but all of the cacti I have, regardless of whether or not they've been hardened (trained to live outside), they become bleached and die. And despite any notion you might have that cacti can go long periods without water... that's true... but they DO need water. And if they are using up their reserves, they won't grow, which is why you should give them a little water about once a week.
Also, CARBONATED water will make them (or any plant, for that matter) grow faster. So Soda Water is perfect if you want to speed up the process a little bit of any of your plants. And why does this work, you ask? Plants breathe in carbon dioxide. I'm not sure exactly how it's absorbed through the root system, but it works from seed to to seedlings to small plants to large plants, so it can't just be the carbon dioxide being absorbed through the leaves or stalks.
Tricocereus, especially, thrive like crazy and will grow unbelievably quick if they're grown outside as opposed to inside with just natural light coming in through a window.
If you start out with a foot, cut the new growth off after the next growing season and plant that section. The mother will produce a "pup" in it's place when it's time to grow again.
The pups will generally grow at least 6 inches in the summer. I break them off when I take the cacti in and replant them and give those clones to good friends who I know will take care of them.
Or you can simply start cloning from the mother plant.
They don't grow retarded, they just will stop growing or grow much slower when the light is shorter and their is less water. Which you should reduce both of in the fall/winter period if you're in a temperate area.
When does the growing season end... if it arrives in like a week or so do I still have a few weeks of growth in a greenhouse before they become dormant for winter?
If you have a heated greenhouse and you can maintain an temperature of around 80 degrees year long without too much humidity, I would just keep them in that year long round.
I would just plant the mother and let her root and continue to grow.
Can I repot it before the plant becomes dormant for winter?
Yes, they're extremely hardy. I've replanted mine up to four times a year without them displaying any signs of shock.
Also, once winter starts can I just place it in my garage' It gets very cold in there (probably 0-10c) and very little light enters... would this be a problem at all?
You can store them in a cold dark place like that if you want, but it shouldn't drop below freezing. You'll risk injuring the cacti... you have to remember, they store water for dormant/dry seasons. The water inside of them can freeze.... thus your cacti would die. I know there are some cacti that can withstand it, but I have no idea as to what species.
I simply take all of my cacti in for the colder season and just keep them at room temperature with natural day light. Some of my original cacti have been with me since I was a child... over 25 years.
I was into cacti as a child before I even knew the magical properties certain species had.... but I certainly took a more serious interests in them after I discovered those properties..... I've never eaten any trichocereus... of which I have several species of. I think of them as having souls. It's just nice to know I have certain compounds around me in plain site and nobody will ever know or do anything about it.
