Phase 1. Keep LifeBloom on tank(always), use WG after dispell, swiftmend before add explosion+tranquillity(for first add or second, depends of your raid). You can use mushrooms if you want, you'll have few free GCDs for it. Phase 2. Use Tree of Life here. (you should be ~80% mana atm so use Innervate) Stack LB on each person and refresh it with Regrowth(if it's free) or LB. Use WG also.
Phase 1. Repeat. Phase 2. Don't use ToL(save it for the last phase). Rejuv. everyone for every second wave+WG (that should be enough). Use [Potion of Focus] after 4rd wave.
Phase 3. Start with ToL LB stacking+swiftmend+WG. (second healer save here) Use tranquillity before ToL ends. Continue WG+swiftmend and start rejuv. everyone. Fight should end before you're oom and Innervate should be out of CD somewhere in the middle of the phase.
That's how i did it when i was low-geared 6k spirit rdruid. Most important - DO NOT spam rejuvenation. It's not WoTLK anymore. Sorry for english