Taunted by curly parsley

If there's one thing I struggle to grow it's parsley. My dad on the other hand has it growing everywhere, and self-seeded at that. I struggle so much to grow it (well germinate from seed) that I've given up. Imagine then my delight and despair to see that it's self-seeded on our patio:

And not just once:

My challenge will be to keep this going as we completely replace the patio. It'll be easy to pot these up but much harder to repeat this year after year!