How/where should I prune dracaena marginata stalks?

Greetings all!
I have many dracaena marginata plants in my house, a few of which are very tall (around 8 ft. tall) and which reside in large pots (I guess over 2 ft. tall and 2 ft. in diameter). I THINK they get a decent amount of ambient light. I am sometimes concerned that they get overwatered -- I never water them until the top few inches of soil (finger depth) feel bone dry, but when I stick my "mositure-tester" wand more deeply into the soil of my largest pot, it records that the soil is quite wet (though I never can feel it myself as being too wet). Then again, I have another large pot which the wand typically records as bone dry, even though I water it as regularly as the other pot! And the ill health apparent in the "wet" pot appears to be identical to the ill health apparent in the "dry" pot.
I think my trouble with establishing a decent moisture balance has to do with (1) the size of the pots, and (2) the fact that sometimes my plants are planted in the kind of prepared potting soil one gets at nurseries for indoor plants (wet pot), and sometimes I amend that potting soil with the regular clay-ish dirt that is native to my area (dry pot).
But, getting to the point of this post: I have several dracena marginata whose new growth looks tired and feeble. I have been unable to fix them by alterring light and water conditions, so now I just want to cut off the long stalks (with a handful of perfunctory fronds at the ends) at some point and see if new shoots appear at the cut. Where should I cut these stalks? Around the middle? Near the base? How should I encourage new growth at the cut points? I don't really care too much about propagating the sickly halves that get cut off, but if do decide to propogate those, how should I go about it?
Also, are there any particular fertilization policies one can recommend for dracaena marginata?
Thanks very much for any help! These plants provide an important decorative element for our home, and had been doing fine for about the last five years that we have lived here, and it is really frustrating to see them go into this decline.
Chuck
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From what you say, you have many more problems than needing to cut back your plants.
The plants are most definitely in pots that are too large and are suffering because of it. The soil may be stagnant, septic and killing the roots of the plants.
Does the soil have a foul odor?
Do your pots have drainage holes in the bottom?
If not, all the plants will need to be repotted in pots the appropriate size with drainage holes in the bottom and saucers underneath..
What do you mean by ambient light? Are you saying the plants don't get any direct light?

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or they have been too long in one pott and exhausted one particular nutrient. But collapsed soil ( what stan sez) is quite possible. I avoid both these problems by replacing some of the soil and add in a few earthworms and some manure every year.

if not, that would explain the bad soil. It should not be too much work to pull out one plant, check that it is not rootbound, check the soil quality, and replace some of it.
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Hello all.
Here are a few updated comments in response to questions:
The soil doesn't smell foul at all. The pot has holes in it, and the soil seems to drain very well. It is hard for me to pull these dracenae marginata out of this large pot to repot them, but I did yank them part of the way out a few months ago and added a pretty good amount of fresh soil. At that time I was able to determine that the roots are not root-bound. I have not observed any difference in the growth pattern or overall health of the plant since I added the new soil.
There is a large window (2.5" wide x 6" high) right next to this plant, but we keep the blinds on this window about half-closed most of the time, so this plant doesn't get much direct sun (except for the bits that seep through the slats in the blinds). There are a whole bunch of other light sources in this room (such as two sliding glass doors), and the room is generally what any reasonable person would consider "bright," but this plant doesn't get any bright direct light from any source.
There are a bunch of VERY healthy dracenae warnecki in this same pot, so apparently the light/soil/moisture conditions are about perfect for that member of the dracenae family.
Chuck
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