Spotted some issues right off the bat. I'm writing the first half of the post assuming you're staying mono green.
Lands - 19 is way too few. I play a GR devotion list and play 23, that's with all the ramp etc. I highly recommend going up to 23 minimum.
Creatures - Mono green is a little less about ramp and a little more about aggro. You need exp 1, a full set of kalonian tusker, move the mistcutters to the side for any blue matchups.
The acolyte is too slow, get some elvish mystics in there. Witch stalker can be used as sideboard card for monoblack or blue, those need to be moved to the side though.
+ 1 scavenging ooze at least. Nuke the vastwood hydra from orbit. You don't need the deadbridge if you're running poluk or vice versa, they're fighting for the same spot in your deck.
Other spells - omg yes, 3-4 garruks is awesome sauce. + 1 nylea, and you can use pit fight if you need removal,but be mindful it can't target master of waves. The bow is okay too, you could +1 that as well, into the wilds is garbage. Do not run it.
Sideboard - aside from the things I mentioned. bramble crush is a great side board card, you need some number of plummet as well for desecration demon.
Now, all that being said, Green devotion is a fine deck. I believe however that the GR version is stronger in the format. This is the list I've been using. It's fun to play imo, and it runs pretty well. I would really really love another domri for it though.
http://deckbox.org/sets/529877
a turn 2 domri is crushing card advantage that control must answer. this deck is also possible to get out a turn 3 garruk.
turn 1. elvish mystic
turn 2. nykthos, burning tree, burning tree, into arbor colossus
turn 3. garruk, swing 6?
I have also been able to burn someone out with clan defiance. I beat mono blue doing that, I had polukranos on the board vs his army of elementals, etc.. I had enough devotion to wreck his board, he was holding open mana for a rapid hybridization.
It went like this. He was on the play so it was my turn 4, after his turn 4. land drops every turn.
turn 1. elvish mystic
turn 2. nykthos, burning tree, burning tree, voyaging satyr
turn 3. tap nykthos for 6, untap with satyr, floating 4, add 6 more play polukranos, arbor collosus
Turn 4. tamp mystic and another land to activate nyk, leaving up a single red, produce 11 mana from nyk, drop a 2nd nykthos, produce 11 more floating 9, total of 20, untap with satyr, floating 18, produce 11 more, tap my red, clan d for 28... (I think i did the math right there)
He was sure I was going to monstrous poluk and was waiting for the trigger. You won't always hit the double burning tree, but when you do...