Devotion to one or more groups of plants

Clematis 'Pagoda'

"Specialising in a hobby of any kind greatly increases its interest, and in the culture of flowers it is desirable to devote oneself more especially to one or two groups of plants, though not to the exclusion of all others; for a garden devoted to one kind of flower only  lacks interest during a great part of the year."  (In My Lady's Garden by Mrs. Richmond, London: T Fisher