Buddleia alternifolia is not one of the more common Buddleia davidii - The Butterfly Bushes. It has an arching weeping habit, and needs different pruning to the common types of butterfly bush.
It flowers on wood (growth) made the previous year so its pruning needs are different.
Because of its weeping habit, it will make a spectacular flowering tree or even large hedge.
The flowers are sweetly scented - especially in the evening.
Buddleia alternifolia - so named because it bears its leaves alternately along the stems, (Butterfly Bushes) have their leaves in pair!
Early to mid summer flowering garden shrub, which flowers on stems that were grown in the previous year. It therefore needs pruning right after its flowering period, in order to allow new flowering stems to grow before the onset of winter.
Prune old flower stems on your Buddleja alternifolia back quite hard (about one third of the way) immediately after flowering. This will allow time for long arching weeping stems full of flower buds for next year to grow. Do NOT prune this Buddleia in the spring - which is the normal pruning regime for the Buddleia davidii types.
The main thing to understand about pruning Buddleia alternifolia, is that it flowers in late spring or early summer, on growths made in the previous summer. This process starts before the flowers have died. You will see that at flowering time, it also has a flush of new growths that started earlier. These are the growths that will flower next year. If you cut back hard, you are cutting off next year's flowers. Prune it as soon as the flowers have died, and mainly simply cut out the flowered branches.
If grown as a large shrub, then also prune some of the older stems right back to the ground. new growth will soon shoot out again. If grown as a weeping tree - firstly make sure that it has a good thick stake. The top growth can be cut back very hard - more than halfway - to allow the new weeping branches space to grow. Prune all flowered stems in this way.
If you grow Buddleia alternifolia as an attractive weeping, flowering hedge, then clip back to old wood in July at latest - right after flowering, then no further pruning until after flowering the following year. Not a hedge for confined places or near footpaths.
Also Pruning Buddleia davidii types
Cornus alba, stolonifera and sanguinea