Choisya is a genus of 7 species of evergreen aromatic shrubs native to Mexico and SW USA that will grow in any well drained soil, acid or alkaline, full sun to light shade.
For the most part they are hardy in the UK. Choisya White Dazzler has proved to be one of the hardest of the cultivars coming through -20°C in the Netherlands.
Bob Brown in the BBC Gardeners World programme in 2016, video below gave it 10 out 10 for best flowering and hardiest of the Choisya
Also with so many flowers it must be one of the best for scent.
I started crossing Choisya in 1982 and have continued every year since, I have introduced six , thousand seedlings have been rejected
Four NEW uniquely different cultivars are being trialled.,