Yes, you've got it right, chop away. Plant it and don't water it for a few weeks, a big piece like this has plenty of reserves but getting wet too soon might cause it to rot.

If I might add...

I have to ask why your plant has chosen this time to send up an offshoot with roots and the fact that you state the lower "main trunk" is shrinking and shriveled.

Perhaps there is a problem with the roots. Perhaps a rot or insect like root mealies. Perhaps not enough water. Maybe some fertilizer. Have you repotted it ever?

It might be hard to assess the problem with a 9 foot cactus though. But if it were mine and it was drying up, I'd like to know why.

Hopefully you will get that cutting with roots attached. Maybe keep the rooted part out of direct light and make sure it will be able to breath so that the cut area will dry. Let the cut dry about two to three weeks to form a dry callous and then plant it and it should do well. Some people prefer not to put freshly cut cactus directly in the earth even if it is dry soil, as it might be a source for bacterial or fungal infection which might infect the cut.
Easy on the water for the first month or two. Make sure it dries out completely between waterings. A loose well draining soil would be good.

Good luck
Wazungy

Wazungy,

The off shoot started in December of 2006 as a small nub. It has grown about 3 feet tall in the past 7-8 months. It is amazing how fast it has grown. The cactus sits in front of a single plate glass floor to ceiling window. It gets direct sun all day. I water the catus about once every 2 weeks in the summer, and give it fertilizer about once a month.

I have no idea why the main trunk is drying up. The upper shoot gets water though. It appears to me that the main trunk is just old and this is natures way of getting its offspring ready to go. I'm no expert and this is just my guess. Are you sure about letting the cut seal for about 2 weeks before I pot it ?? Do I just leave the shoot on its side in the shade or sun...I'm worried..

Thanks all for your help :-)

Your Cactus sounds like a Cereus (like peruvianus). If it has dried up on the bottom, it may have died on you and the reason it sent out the shoot IS because it is dead. The cause could be anything. I'd cut the shoot off and pot as mentioned by others and then cut the dead part off and keep cutting up the original stalk until you see no sign of brown or black flesh. Then just let that section sit for about a month or so and it should form a callous over the cut section and you should be able to pot it. You can just stand it in a corner on a piece of paper until ready to pot. As a previous poster stated, it has enough reserves to be just fine.
Good luck.. Try posting us some pics ;-)

I am in the same situation of that is posted above (h20baby). I have 2 plants,(Cereus) not as tall, however,(maybe 4-5ft. tall). The bottoms are the same as explained above. I have made 4 freshly sliced cuts and layed them flat in a strong box, covered w/ a sheet. There are holes on the bottom, for air circulation. Is laying them flat, OK? Or should I stand them up? The longest cutting stump is no more that 20" long. 2-3 weeks seems a long time to allow them to callous over, is this the correct amount of time, for sure? And when I plant them in the ground, I am to make sure ground is dry, and wait another 2-3 weeks before watering, even though they are calloused over well? Also can I just keep chopping cuttings off the main 2 plants that I have?, Down to just above the bad spots on ground level. I would like to get rid of the 2 plants anyhow. I realize that I will have 2 exposed spots; one will eventually be in the ground, will the other end, just callous over and be OK?
rsf7,,,,,Scott.......

Oh, I have not checked this forum for a while, your question would have been more appropriate for the ordinary Cactus and Succulents forum.

> Is laying them flat, OK?

Yes, if they stand up they will not heal as well.

> 2-3 weeks seems a long time to allow them to callous over, is this the correct amount of time, for sure?

Actually it is a short time, I am more used to months ... But it also depends on species and climate.

> And when I plant them in the ground, I am to make sure ground is dry, and wait another 2-3 weeks before watering

Yes, at least. It cannot take up water before it has grown new roots anyway.

> can I just keep chopping cuttings off the main 2 plants that I have?

Yes.

I apologize for posting in the wrong area. I saw the question above, and that is what I needed to know.
Thank you for your answers. If you happen to see my post here again, I read somewhere to plant them only 1 or 2"s' deep, even though some of my cuttings are, 4-6" in diameter? They'll fall over, won't they, no matter how tight I pack them w/ my boots?
And how do I find the 'ordinary cactus and succulents' forum?

The other forum is in the link below.

Cuttings can be buried deeper if they have healed well and grow roots quickly, and columnar cacti usually do. Otherwise I support them in some way.

Here is a link that might be useful: Here

I would like to know how to transplant some of my
Prickly Pear Cactus- they ;are 2 years old and
they are awesome in flowering. One Prickly Pear has
over 150 beautiful rose colored flowers.
thank you

Hi Joan,

I don't think this is quite the right place for this question. Try the Cactus & Succulent forum nearby (see top of page), not the Picture Gallery (here), few folks come here anymore.

I don't grow Prickly Pear (Opuntia) but am under the impression they're easy to root. I believe you can just pot them up dry from cuttings if you leave them out for a few days after cuttings to callus over.