Indoor cactus during winter - switch growing/dormant seasons?

Question

I have a small decorative cactus (exact species unknown, but I'll attach a picture) and one west-facing window next to both the air conditioner and the heater. I have no other windows. I have no outside space. My last cactus never grew and died in the space of a year.

Should I try to encourage growth during the winter (when the heater is running) and dormancy during the summer (when the AC is running)? Should I take it away from the window during either season? Is there anything else I can do to give it its best chance of success?

I've taken the picture so that the heater and AC unit are both visible. The cactus itself is about 3 inches tall in a 3-inch pot. The heater runs under the full length of the window ledge directly next to the plant, and the AC (right corner) blows out into the room, not directly on it. It's night as I'm taking the picture, but this window is usually sunny in the afternoon with nothing blocking it.

Answer 1

This looks like Pilosocereus, maybe P. glaucescens or P. pachycladus.

Your situation is not ideal, but I think you can work something out. I had the same setting for winter (west facing window, with heater underneath), but during summer I have no AC, and I put most of cacti outside in the full sun.

The normal advice is always: put the cactus during winter in a cold room (~10-15C) and with much light, and stop watering it. This is especially true for large cacti, however smaller ones like yours do need some water once in a while during this period. And in your situation, with heater, you should give it even a little bit more. What I did last winter (which was like your situation above a heater), I watered them a little bit every month. Only to not let them dry out, but be sure not to give them too much and too often. Important is to not let them start growing in the winter, you'll get leggy growth (etiolation).

What to do in summer, I guess just give them water when needed. So when the soil is dry you can give it more water. Especially when you see new growth, so you know it is active and not dormant.

You ask if you should encourage growth in winter and dormancy in summer, this is not a good idea. Cacti need light (direct summer sunlight) to grow, if they grow during winter there is not enough light, so you'll get ugly leggy growth.

Hope this helps, good luck and enjoy your cactus!