I'd also like to add that this is available to Controllers, Defenders, Corruptors and Masterminds
Masterminds of which get a different Tier 9 power called "Fungi Pods" (basically a mix of 'Detonator' and 'Noxious Gas')
I think thats all now, please Comment 
A total of 14 of my nerves have been harmed in the making of this post...
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*Spirit Tree in the Plant Control powerset would be replaced by another power as it is a buff
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You're suggesting the devs remove a power from a powerset that is already in the live game and replace it with something else, when some players who have/like spirit tree would be in uproar about it, and when the devs have already said they won't ever remove/replace powers in existing sets?
Yeah I can't really see that happening.
Some of the powers look ok, others look totally overpowered (Nightshade Patch is both an AE hold patch AND a -res -dam power?) - my biggest worry is that this set looks more like a control set than a debuff set - you have FIVE control powers in there - that's more than Dark Miasma or Rad Emission or Storm Summoning, which are already rather control-heavy debuff sets (and I love all 3 of them, though your set doesn't really appeal to me).
Take the hold off Nightshade Patch and that's ok, you could even have some minor damage on it (like Freezing Rain has). Move Toxins later, maybe to the same position as Petrifying Glare in Dark Miasma (T7) - T3 is too early for a hold in a debuff/buff set.
Possibly turn the heal into a PBAE (but really that's just my dislike of single target holds showing through) and either take the resist off it or keep it low and put +perception on it perhaps. Instead of Spirit Tree, which is already in Plant Control, perhaps put in a PBAE-cast regeneration buff, or even a PBAE heal if you want to stick with a single target heal in the T1 slot - placeable buffing items really aren't that useful in fast-moving teams unless you're on a long AV/GM fight.
Get rid of Exploding Fungi - targeted AE knockback is less than useless in most teams - perhaps put in a powerful single-target buff that you can't keep on the whole team all the time (akin to Frostwork or Forge), maybe one that adds considerable +regen or grants an aura of vines that slow/damage all targets near the ally you cast it upon.
Poison Ivy is ok I guess (sounds identical to Quicksand which is a control power, but the -def in Quicksand is so high it could work as a debuff too - though it would mean some redundancy for Earth/Plant trollers who would only need one of them, really), as is the resurrect, but you have to get rid of the confuse at T9 - confuse is a very powerful control and apart from Ninjitsu's confuse power (which is fairly limited) the only reliable confuses are in Control sets. Plus this is supposed to be a buff/debuff set. How about a PBAE buff that makes allies' skin as hard as bark, absorbing or deflecting damage, giving 15% resist and 10% defence (both enhanceable) against all damage types EXCEPT fire (burns plants) and psionic (bypasses the bark skin)?
Then just re-order the set accordingly. It's your idea, so I won't do it for you - the pleasure of revamping it should be yours. Look at other debuff sets in Mids Hero Designer if you're not sure what kind of powers fit debuff/buff/heal sets.
Hmm, I guess I'll keep The good ones (with your weaker effects) and Re-Arange them into good Tier levels, but replace the bad ones like Exploding Fungi and Spirit tree and replace them with something like:
Spore Barrier (Ally Armour,+ Res Confuse, Hold, Immobilise, Sleep, Psi, Toxic)
Bark Armour (ally Armour,+ Res Lethal, Smashing, Toxic, Energy, Neg Energy)
A total of 14 of my nerves have been harmed in the making of this post...
I cant think of a good name for this powerset, but basically its a Plant Buff/Debuff set, I think the Plant types could extend into this frame of powerset, so here goes:
1) Healing Herbs (Ally Heal, + res toxic, psi, Stop Disorient)
2) Nettles (AoE foe slow, - res toxic)
3) Toxins (foe -Res Toxic, Smashing. Hold/Vomit)
4) Spirit Tree* (Targeted Area ally + regeneration)
5) Awakening Medicine (Ally Resurrect, + Res Toxic, psi, energy)
6) Nightshade Patch (AoE -dam -Res all, Hold/Paralise)
7) poison Ivy (AoE -Def -speed)
8) Exploding Fungi (Targeted Area foe Knockback, Toxic DoT)
9) Blinding Spores (Cone, Foe -Preception -Accuracy Sleep Confuse)
*Spirit Tree in the Plant Control powerset would be replaced by another power as it is a buff
If you'd like to comment or offer up other powers, please do, And a good title for the powerset would be much apreciated
A total of 14 of my nerves have been harmed in the making of this post...