Even in limited, I'd always pick a Rampant Growth above the Petal. Permanent ramp is so much stronger, except if you ramp out a Hypnotic Specter on t1 or a Phyrexian Obliterator on t2 with Dark Ritual. I don't see the petal doing that much, I like Chromatic Star much more in its place, even if it's just fixing, but also a cantrip.