I play a plant/energy dom and have no problems soloing.
It can be a little slow because dominators don't have the greatest damage output around but now I've got the flytrap there's a little ravenous bud to help me out!
On the energy side, power boost helps with the confuse duration (seed of confusion is mass confuse you can take at level 8 IIRC, very handy) and hold duration on IMO the not as good as i was expecting Vines.
I would advise getting stamina early too, but that's pretty much a given these days.
As I said, soloing is not a problem and with the plant set you get one of the coolest looking pets in the game!