One of our favourite non natives for the roof. We always add this to the seed mix, it’s yellow flowers often dominate the roofs in the second and third years. Despite often growing over the whole roof, it doesn’t overpower its neighbours, and the flowers held up on single stems allow plenty of light and space for other plants. The foliage has a feathery grey/green colour contrasting with the bright yellow flowers. A must unless you have to keep to all natives.