| Buddleja davidii|| 'Blue Horizon'|
| Summer lilac, Buddleja davidii 'Empire B, Buddleja Lo & Behold 'B, Buddleja davidii 'Adokeep, Buddleja davidii 'Tobuivo|
Buddleja davidii 'Blue Horizon' is a cultivar introduced to commerce in the UK by Bob Brown, Cotswold Garden Flowers, in the early 20th century. It was accorded the RHS Award of Garden Merit (record 677) in 2010, by virtue of its superior sapphire-blue hue, relegating 'Empire Blue' to the Sunset List for rescission of its AGM. 
Buddleja davidii 'Blue Horizon' Wikipedia
'Blue Horizon' has a compact habit, growing to a height 2.7 m, with a spread of 2.6 m. The arching branches bear greyish-silver foliage complementing the clear blue terminal panicles which average 44 cm in length. 
'Blue Horizon' remains uncommon in cultivation, and is not known (2012) to have been introduced to North America. In the UK, it is included in the NCCPG National Collection held by Longstock Park Nursery near Stockbridge in Hampshire. Hardiness: RHS H5, USDA zones 5–9.