Hello!
In 2009, we bought a cactus (100_1233.JPG). It had a red flower on it. Then, in 2010, the flower wilted (100_2017.JPG on the right). From 2011-2012, the cactus grew "arms" with roots on them (100_0247.JPG). It never grew a flower back. We cut off one of the "arms", planted it in soil, and it grew as a whole new cactus plant (100_0251.JPG). Is there a way to make the cactus grow its flower again? Why is it growing all the "arms"?
Thanks!
The red part isn't a flower, it is a different kind of cactus. What you had was made by grafting two different species of cactus together. Basically they grow the green cactus and red cactus as normal, then chop the tops off each and put the top of the red cactus on the bottom of the green cactus. This helps the red cactus to grow better, because the green cactus may have a better root system.
Unfortunately it sounds like your red cactus has died and only the green cactus is left. The red cactus will never grow back.
Search the web for 'cactus grafting' to find out more.
stimmer:
The red cactus will never grow back.
Unless you grow some red cactus.
I did not know that they were two different cactus. So the red cactus died, and the green cactus is growing like crazy. Why did the red cactus die?
Why did the red cactus die?
Rejection?
Pining for the fjords?
Cactus die. Sometimes there's no explanation for it, sometimes it's over watering, too little sun, too cool, etc. The post above is correct in that this is a grafted cactus, so you can get another red one and graft it on (easy) to restore the look. The green one is a 'runner' cactus, it puts out arms that contact the ground and take root spreading the cactus. It can cover the ground where it is planted in a few years. It will always put out runners, that's just the way it is.
Cactus grafting is a bit of an art form. Almost any cactus will graft to another easily, but keeping both the graft and the root stock alive long term can be a problem. The different sun and water requirements between the two cactus can make it impossible to keep them both alive. Like the other poster said, look it up, there are lots of great articles on this kind of thing out there.
Also - different catus have different growing habits and different flowering habits. Some will flower when it is dry, some when wet, and some are more seasonal. Just about any cactus will grow if a piece is stuck in soil and given the right moisture conditions.
How can the red cactus get nutrients, water, etc. it is not touching any soil?
Like any other graft, I assume.
Okay, I will reword my Reply #7: how can a cactus, grafted on top of another cactus, get water, nutrients, etc., when it is not touching the soil?
OK, at this point you need to resort to google and take a look at grafting in general. It's commonly used in horticulture so you shouldn't have any trouble learning about it.
holy crap. I didnt know they were 2 plants. I bought one in a small clay pot maybe 3 inchs tall 7 years ago. Had it with the red cactus for maybe 2 years. It finally got neglected long enough that the top part died. I transplanted it to a bigger pot and have moved it from house to house ever since. Its now huge with arms coming off all over the place. I trim the roots off every once in a while. I almost killed it a few times from over watering and now just give it a cup or so every couple weeks. It lived through a catapillar attack. Root rot. And what i call general malaise.
My wife hates it but I call it the only symbol of our love since I got it for her before we were married. lol.
I keep waiting for it to grow a new red thing. guess thats not happening.
I guess growing arms everywhere is the green cactus's way of reproducing.
draythomp:
OK, at this point you need to resort to google and take a look at grafting in general. It's commonly used in horticulture so you shouldn't have any trouble learning about it.
No luck on finding out how the top cactus gets nutrients. My best guess would be that it draws nutrients from the bottom cactus.
My cactus died recently and I have my suspicions why 
As well as looking up grafting look up pleaching.
Some of this stuff is mind blowing - you need a bit of time though
http://dsc.discovery.com/news/briefs/20060116/treehouse_tec_zoom1.html
dkl65:
I guess growing arms everywhere is the green cactus's way of reproducing.draythomp:
OK, at this point you need to resort to google and take a look at grafting in general. It's commonly used in horticulture so you shouldn't have any trouble learning about it.No luck on finding out how the top cactus gets nutrients. My best guess would be that it draws nutrients from the bottom cactus.
I believe that a graft uses the vascular system of the parent plant to draw nutrients from the soil, just like a 'natural' branch of the original plant.
I have heard the prickly pear of that type cactus is good eating, and the cactus itself is robust.