Again i still use the way A Slice of Life described pony "war" and it's my headcanon.
There used to be rather bloody and costly wars with neighboring knigdoms as they fought for land, resources, etc.. but centuries ago the leaders all realized what a waste it was, settled things peacefully and well just stopped being idiots. (Of course since this seemed to be shortly after Celestia baniched Luna to the moon, the rest could have just not wnted to risk joining her.)
But, they realized that there will always be hotheads, or overly militant ponies, gryphons etc... that simply want to fight. And that to help keep the aggression and what not in check, and keep wars from really happening. They would stage mock wars regularly with each other, using foam swords, water balloons, pies etc...
Also explains OAB, it's been so long like that, it's simply how everypony and buffalo thought "war" was fought, and just played along.
Word Of God, they can, but not effectively as EP's. They'd be able to grow like a personal vegetable garden or something, but not the large amounts needed to feed everyone. Plus the EP's can grow it faster, better, and in worse coditions.
edited 27th Mar '13 8:13:32 AM by Seraphem