Large white bougainvillea

While bougainvillea also are found as summer plants in colder areas such as central Europe - bougainvillea typically is a pure tropical country and bougainvillea thus loves plain sun hot - rainy season wet and dry season many months zero water needed.

If you start to irrigate bougainvillea during blossoming/dry season - then you may expect all the blossoms to get lost within days. If you want to irrigate - the water only the roots and never the top of plant itself.