We have seen druid healers in siege that do some really serious heals to gates, that I as a healpriest cannot come close to competing, I have currently a lv 90/70 druid/warden and am trying to find out what skill I need to do, to do heals like that

(gear and stat tips for a gatehealer would be good)
and I heard that I can use a staff and stat like a mage on my w/d side because it has a skill that works with mdmg... I have not found that skill altho I did see one broke one Earth spirit Essence, is this the one and is it still broke?
thank you