I've owned the PC version of this game since it first came out in 2009. I've lost count of the number of times I've played that version, and the DS version is turning out to be the same. There are some differences between them. You get a maximum of 9 seed slots instead of the 10 you can upgrade to on the PC version, but that's because the DS screen can't display any more than that. There's one level and mini-game where you have to shout from time to time - warn people when you're about to play that game or level. You still have the Tree of Wisdom, but you can't change the appearance of the zombies (no keyboard, obviously). Some of the awards are different, too. You also have the option to play against another player. One of you plays plants, the other plays zombies. I can't comment on that aspect of the game because I haven't tried it yet.
The game is played on the interactive screen, with the other screen used for the timer bar. Don't ignore this screen, though. Strange and interesting things happen there.
I play this version on a DSi XL. I've not played it on my DS Lite and I suspect the images would be a bit small on the smaller screen.