I really do not think Petal is a roamer. Yes, you will go into the jungle to help your team or secure resources, but that is not the ideal place for you.

On top of not having much resilience and only one active ability for burst damage (with a long cooldown) using your B ability actually creates a ridiculously large visual, as if you needed your position telegraphed while in he jungle.

For sure, Petal is great at taking out the miners and/or blasting people in team fights, but you really don't want to hang out there at all like another hero might (like Joule).

Another thing I find is that countering another Petal really depends on a lot of things. If you have built crystal power and your opponent has built warhorn and tornado trigger (for example) then it is entirely possible that they will be able to blow up your minions before they wreak too much havoc.

Another side note: if you are facing another Petal, make a dump of three seeds and stand in it as you fight, letting your own minions die. When the enemy Petal sends the minions to melee you it is likely that sprouting your seeds at that moment will severely damage/destroy them, giving you a massive advantage.