I did a little Googling, and it turns out that even WITHOUT JAILBREAKING or pirating anything in any way, PVZ 2 can be installed on an ipad 1 if you're willing to jump through a few hoops.
I more or less followed the instructions of Joe White from this link, substituting PVz2 instead of iPhoto:
1) On your computer, download Plants vs. Zombies 2 from the iTunes app store.
2) Install Apple's iPhone configuration utility:
3) plug your iPad in and sync with itunes (mine gave me the message - cannot install this app, yadda yadda yadda. That's fine)
4)now, launch the iPhone Configuration Utility. If Joe White's instructions from the link work for you, you're set. But if it doesn't, here's how I did it.
In the iPhone Configuration Utility, under "devices" on the left, I chose "add new item to library". In my computer, pvz2 was:
C:\Users\Marcina\Music\iTunes\Mobile Applications\PvZ 2 1.2.ipa
Change to your user name
Then on the left side in the Configuration Utility chose Your iPad and look at the list of apps. PVZ 2 should be in that list with the option to "install" on the right. Do it, and you should be good!
Mine worked right away, and I played to the fourth level until my children pried the iPad out of my hands. In honor of this game, they are getting an extra half an hour of ipad time this week (to a total of 1 1/2 hour for the week).
Last important note, and I'll quote from Mr. White:
"But there is one problem. The next time you sync with iTunes, you'll get an error message claiming that your iPad isn't authorized to use the iPhoto app – the only way to get past this message is to hit the "Cancel" button (authorizing the iPhoto app with your Apple ID won't help). If you click "Don't Authorize," iPhoto will be removed from your iPad and you'll have to repeat the above steps."
Hope this helps someone!