The plant is getting very tall and I would like to divide it in the middle. Is that possible? If so, how?
It is most likely growing from one stem and can't be divided.
You can propagate cuttings to keep the plant going.
This article has more information.
https://www.gardeningknowhow.com/ornamental/cacti-succulents/pencil-cactus/care-pencil-cactus.htm
Pencil cactus now 6-7 feet and there is a large crack in driveway branching out from where the plant is located.
A Pencil Cactus does have an extensive root system. If it is causing the damage, I can't say...but it does sound like it may have in your case.
I was given 3 cuttings several years ago. The cuttings have been neglected for about a year - they weren’t dead but they weren’t growing either. I recut them, let them dry out then planted in soil for succulents. One died almost immediately, one is growing nicely, and the other one has done nothing going on 3 years now. Both surviving cuttings are in the same location and getting the same attention. Any ideas or advice?
Cuttings need more water than when the pencil cactus becomes established. Could it be they aren't getting enough water? Here is more information:
https://www.gardeningknowhow.com/ornamental/cacti-succulents/pencil-cactus/care-pencil-cactus.htm
This just started this spring after overwintering in my inside sun room, which is pretty cool in the winter, but not below 62 degrees. I did water it a little in March.
Our experts say Euphorbias are notorious for throwing leaves and segments when traumatized by temperatures too low or drought. The plant is trying to conserve its resources by "downsizing". And, this plant is a succulent; don't keep it wet. Let it dry slightly between waterings. Here's an article about caring for your plant:
https://www.gardeningknowhow.com/ornamental/cacti-succulents/pencil-cactus/care-pencil-cactus.htm
seems like similar material to tea bags
I wouldn't. Those chemicals will be taken up by the plant, and not likely destroyed by composting. Personally, that isn't something I would feel comfortable putting in my body. Instead, I would use teabags. They are a similar material WITHOUT the chemicals.
The plant is about six years old and at one time was over ten feet. I cut it back to about four feet several years ago. It now has a younger middle trunk growing about the original one. I haven't looked closely at the plant for at least a month. The black plaque- like patches are on the original trunk, heavier towards the bottom. It appears that are moving upwards. The upper plaques are smaller in size.
It may be stem rot. This article describes the problem and how to correct it. I also would take some cuttings off the top of healthy tissue just in case you lose it.
https://www.gardeningknowhow.com/ornamental/cacti-succulents/scgen/stem-rot-of-cactus.htm
I have a pencil cactus that is approximately 6 foot tall and I have over looked the white spots on the branches and trunk. When realized the white spots were not from taking cuttings I found an article that advised putting alcohol on the spots. I have been doing that for about two weeks. Last night the trunk was green and on the bottom of the trunk which I had been putting alcohol on was green (which had been white prior) Now the complete trunk is white. Am I slowly killing it or is this killing the infestation which must have been deep. Please advise me how to proceed. I really don't want to lose it.
I think it looks more like powdery mildew than a pest. You can try Neem Oil, it should help in either case.
https://www.gardeningknowhow.com/houseplants/hpgen/powdery-mildew-treatment.htm
https://www.gardeningknowhow.com/ornamental/cacti-succulents/pencil-cactus/care-pencil-cactus.htm