Why not take 2+ levels of Holt Warden? Fit's the nature concept and gives you rebuke plants to fuel DMM.
This is not correct. Divine feats explicitly mention turning/rebuking UNDEAD (not plants or fire creatures or oozes.)
There ARE several alternate class features/sub levels that call out as counting as turn/rebuke undead for all purposes or specifically for the purpose of divine feats.
Those include:
Cleric 1, Azurin racial substitution, Magic of Incarnum - gain Channel Incarnum instead, but counts as turning for feats
Cleric 1, Dragonblood substitution level, Races of the Dragon, turn energy instead, counts as turning for feats
edit: Seems like I wasn't on the last page. This has been addressed.