Very good and very complicated question.
Just a little list of the things I think this power does.
1. Creates a patch on the ground that slows foes within it - causes aggro to the user.
2. Summons an invisible pet at the center of the patch.
Pet:
1. Has a power "Summon Vines" and uses it every 10 or so seconds. This is an area of effect power and if it hits, summons a vine for each enemy it hits.
2. Has a slowing aura around it.
3. Follows the user around and acts like any pet would.
Vines:
1. These have hit points and last about 10-15 seconds.
2. Flings thorns at the foe they appeared nearest to.
3. May have similar characteristics to the vines in the respec trial in that they slow their enemies down.
Now, the procs may trigger off the aura of the pet and or the patch on the ground where you activated the power.
Anyone else know better?
I thank you for responding, but I really need to clarify my question. The "Chance for" I was referring to was not the chance for the vines themselves to pop up. What I was looking at was the possibility of slotting either Force Feedback: Chance for +Recharge or the Pacing of the Turtle: Chance for -Recharge piece into Carrion Creeper. When is the chance on a slotted enhancement determined when placed in this particular skill?
Bael,
I think that WAS what he was talking about. The proc may have a chance to trigger when you cast, when the invisible pet does stuff, and when the sub vines do stuff. But he wasnt sure, and neither was I. But the chance for the proc enhancements to trigger is probably more complex on this power than on just about any other.
Maybe someone will chime in who is totally sure about the details. My plant dominator and my plant controller both happen to lack procs currently so I cant answer with certainty.
Lewis
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It depends on the proc in question.
Positron's Blast will only proc when for the melee and ranged vine attacks, as well as the AoE Entangle.
Pacing of the Turtle will proc every 10s from the -Speed Aura (Note the speed aura is emanated from the invisible pet that follows you around, and causes the vines to be generated), in addition to from every vine attack as they have -Speed enhancing.
Force Feedback will only proc from the MELEE attack of the vine, and would apply for the one vine itself (aka useless for the most part).
Trap of the Hunter will only proc on the entangle attack.
So, the best procs for this power will be the AoE Damage ones, and the Slow ones. The KB and Entangle procs are more or less useless because it effects such a small portion of the powers total effects.
Damage Proc Mini-FAQ
Just noticed Damage Proc Mini-FAQ wasn't working with new forums, it's been updated.
Thank you all for your help. That was exactly what I was looking for. 
You might want to check or ask in the controller forums, as they have carrion creepers too.
I know the enhancement values from IO sets used to only apply to the creeper attack appropriate for that set, but that was changed with i15. Now the damage enhancement from Positron's blast, for example, will apply to all creeper attacks. However, I'm not sure if that also applies to the procs.
Prior to that change the proc had NO effect, now it will.
Damage Proc Mini-FAQ
Just noticed Damage Proc Mini-FAQ wasn't working with new forums, it's been updated.
I have been enjoying my first Dominator greatly, and have found a way to tweak him a bit. Though, before I respec him I would like a question answered...How would a "Chance for" piece work in Carrion Creeper? Is the chance rolled when I initially cast it, or upon hitting an enemy, or does it proc while the creeper is active? Any help would be appreciated.