What is it and what should I do with it?

This 18 inch tall cactus been growing in this same pot along with a shorter one of a different variety for several years. It has only watered about twice a year and has lived on a windowsill without direct sun. Because it is so tall and skinny I hesitate to transplant it, so I am wondering if it could be cut off and just the top parts replanted. The short one will get transplanted with some new soil. Can somebody tell me what they are? The tall one has 5 ribs and small clusters of tiny hairlike spines at the points of the ribs, lower down where the plant looks brownish there are more definite spines.

I'd say that you can cut the top off of the tall one and reroot it. I've done it a couple of times and it worked. (It will be harder to cut than you would ever imagine. Also, you can cut the middle into segments and root each of them and leave the base and it should grow a new stem. I recommend waiting until warm weather to do it.

You can certainly cut it off and root. You may want to just take it the the sunniest spot outside in spring and summer though. I have had a couple of euhorbias that did not branch until they were fairly tall.

Good advise, I would also let it dry in a airy spot, until I see roots, then plant it in the spring. Yes you can cut it into 8" segments, I would toss out the ugly corky stuff on the bottom. You can even put all the cuts in the pot or flat, no soil, be sure to mark which end is the bottom, so you don't get mixed up when planting, and If you do lay them on their side. Norma

Mary I forgot, don't eat any of it. Norma

I'm reviving this thread but still don't know what it is. It was repotted and has been living in my greenhouse for 2 years, has grown a bit, has no branches or buds. Somebody must know what it is.

From this distance, I will hestitate and say the tall one looks similar to a Hylocereus.
Do you have any closer or sharper photos of them?

Hylocereus, Harrisia even some Selinicereus look like that. Hard to ID without a flower.

Some advice. Watering it twice a year is way too little and the plant needs a lot more light. I would cut and re-root about a six inch tip cutting and cut six inch pieces of the rest of the stem. They'll produce new branches that can also be taken as cuttings. I would wait till spring to do this in your climate howhever. You live in a colder wetter climate than mine. I water my cacti as much as once a week in the summertime. You could probably get away with watering every two weeks or once a month even. In a northern clime like yours you can probably grow this plant in full sun as well after acclimatizing it in the spring. With enough light and water it should flower for you. Then we should be able to tell you what it is. Meanwhile I wouldn't change anything. If the plan's survived this long, it will be fine till spring.

Franj

Mary, sorry, I have no idea what it is, but I was shocked that it survived being watered only twice a year. I hate my 2 cactus, my kids make me keep them, and I manage to water them once a month.

I put the pot outside this summer. It does not have a hole in the bottom, so each time it rained or I put the sprinkler on it got watered. I would say 80% of the summer it was in an inch of water. I thought the water would kill them, but no! They are both alive, back inside now and thriving. So now it seems I can't kill them by overwatering them and you are making me think I can't kill them by underwatering them. LOL

I've made my daughter promise to take them with her to college when she is old enough. LOL

It gets watered more than twice a year now that it is not living on a dark windowsill, but is in a greenhouse year around. I do think that I will cut it in pieces and pot them up, it is ugly as it is now. If it ever blooms I will post a picture. Thanks for all the advice.