Can I try Heirloom before I have a farm?

Yes, so you can learn the method and build a practice plan before you break ground. At the first question of the farm setup, choose I don’t farm yet, I just want to try Heirloom.

You get the same 30-day free trial, with no credit card, and the whole app: map an imagined farm, plan its successions, and see what a season asks of you before you commit to it.

The steps are in Set up your farm.