A bit of a suggestion: Try playing the character first before trying to make an end-game build. You need to learn about the powers, what they do and your playstyle with the character before worrying about an expensive end game build.
Plant/Rad is a great combo. It is actually a fairly high AoE damage and high control character. You want to slot Roots especially for damage, not immobilize. Your main strategy in the early game is to run in to just the right position (stealth helps for this), hit the largest number of foes with Seeds of Confusion, and then keep throwing Roots until they drop. Strangler is great to lock down bosses and foes who are missed by Seeds.
For the Rad powerset, take a look at my Illusion/Rad guide on the Rad powers. That will help you slot up the Rad side.
LOCAL MAN! The most famous hero of all. There are more newspaper stories about me than anyone else. "Local Man wins Medal of Honor." "Local Man opens Animal Shelter." "Local Man Charged with..." (Um, forget about that one.)
Guide Links: Earth/Rad Guide, Illusion/Rad Guide, Electric Control
Alright, I'll try that before really investing into the build much. Thanks a ton for the advice. 
When I have some time, I'll come back to give you a rundown of my view of the powers and build. I don't have enough time right now.
LOCAL MAN! The most famous hero of all. There are more newspaper stories about me than anyone else. "Local Man wins Medal of Honor." "Local Man opens Animal Shelter." "Local Man Charged with..." (Um, forget about that one.)
Guide Links: Earth/Rad Guide, Illusion/Rad Guide, Electric Control
Oh, no rush. Thank you again for your time on this. ^^;
OK, Here's my take on Plant/Rad. There are others with different opinions of course . . .
Entangle: Single Target Immob. The main reason to take this is as a single target damage power. In late levels it can be used to Immobilize bosses. This is one of the most skippable powers, but worth considering if you expect to mostly solo.
Strangler: Standard Single target hold. Essential. Looks cool.
Roots: Key power for Plant, because it does twice the damage of the Aoe Immobilize powers from other Controller sets. Slot this for Damage. Basic slotting is 2 Acc, 3 Damage, 1 EndRdx. Note that this will not hit foes if they are more than a few feet off the ground.
Sport Burst: targetted AoE Sleep. Easily skippable, but can be useful solo. It also can be useful to control a group that comes in after you have already used Seeds of Confusion.
Seeds of Confusion: Cone Confuse -- The most important power in the set. Slot it for 2 Acc, 2 Confuse, 2 Rech. Later with sets, you might be able to get some Range in it. You want this up as much as possible. Seeds+Roots is the key to Plant's AoE control+Damage.
Spirit Tree: Skippable, especially since you have a heal. Can be useful for big fights in one place (AVs) or repeated ambushes, but this sits on my bar unused most of the time.
Vines: Ranged AoE Hold. Pretty standard. Good to have but not essential. I recommend it for a power to use when Seeds is Recharging. Also stacks with EM Pulse.
Carrion Creepers: Another essential power, and kind of hard to describe. It creates an invisibile pet that then spawns a bunch of huge vines that attack foes. The vines also draw aggro, so this is a great opening power. The Invisible pet follows you for a little while and then may spawn vines for the next group or two. Slot for Recharge and damage. Slotting sets can have odd results.
Venus Fly Trap: Has several nicknames like Chompy, my favorite is from the movie/Play, "Little Shop of Horrors." The man-eating plant is named "Audrey II" after Seymore's co-worker, but he calls it "Twoey." Twoey is the coolest looking pet in the game. He is kind of squishy and dies fairly often, but can add some OK damage. Twoey is not the game-changer that pets in other sets can be, but still strongly recommended.
Radiant Aura: A heal you have to take, which is a good thing.
Radiation Infection: ToHit Debuff and Defense Debuff autohit toggle on a foe. Essential. Slot it mainly for ToHit Debuff and endRdx.
Accelerate Metabolism: Essential Team buff that does a bunch of stuff in small amounts, including Recharge, Recovery, Damage. Try to hit the entire team with this. Slot for Recharge first, then EndMod.
Enervating Field: Essential Damage and Resistance Debuff, also an autohit toggle on a foe. Activates much faster than RI, but uses a lot more endurance. Slot for 2 EndRdx.
Mutation: Ally Rez power that is skippable but nice to have.
Lingering Radiation: Foe AoE with Slow, -Recharge and -Regen, this is the third essential Rad debuff. This one need Accuracy and Recharge.
Choking Cloud: toggle PB AoE pulsing Hold. Use a ton of endurance and needs to be fully slotted for EndRdx and Hold. I don't like it for a Plant/Rad, but not everyone agrees. See my Ill/Rad guide for the details on this unique power.
Fallout: Situational power that lets you explode the dead body of a teammate. Kind of fun, but very, very skippable. Some people love it, but you have to have a teammate die in the middle of a group of foes, and then you have to be able to get close without dying. Invisibility is pretty essential.
EM Pulse: PB AoE Hold with fast activation and a HUGE area. Also has -Regen and does damage to Robots. Great power, but has a LONG recharge and a minor downside -- it stops you from recovering endurance for a few seconds. Works best as a Panic button power, but can be used with Vines to hold bosses.
That's a quick summary of the powers.
LOCAL MAN! The most famous hero of all. There are more newspaper stories about me than anyone else. "Local Man wins Medal of Honor." "Local Man opens Animal Shelter." "Local Man Charged with..." (Um, forget about that one.)
Guide Links: Earth/Rad Guide, Illusion/Rad Guide, Electric Control
I've never really played much of a support character, and I thought a Plant/Rad would be a nice place to start out.
I'm mostly looking into making this character on Freedom, to have a change of pace from Virtue, and trying to make him a great controller to have along for spamming TFs. However, never really playing support, I don't know if this build is exactly built great for getting as much debuffing out of him without rolling a Defender.
Any tips/advice would be great.