Zone: 5 to 9
Soil: sand to loam
Light: Full sun to part sun
Bloom colour: Range of colours
Bloom period: Early spring or July to frost
Height: 2 to 15 feet
Moisture:Usually dry to medium
Attracts: Butterflies, moths and hummers
Notes: Most people only buy one species - Buddleia davidii. I was hesitant to include this on my recommended list because this plant is an invasive species that does well in disturbed and riparian areas. However, I would rather gardeners know how to manage this plant properly should they decide to plant it because it is widely available. A single butterfly bush could easily produce a million seeds in a single season. The seeds can remain viable in the ground for many years so when the ground is disturbed, the seeds germinate. In Great Britain, this plant can be seen growing in many places, yet it is a native of China.
To avoid causing environmental problems with this plant, it is essential to deadhead and to cut off every flowerhead by October before the seeds have a chance of maturing. If you do not have the time to do this, then be responsible and buy another plant to attract butterflies or look for a buddleia plant that does not produce fertile seed (Two varieties mentioned here include Blue Chips and Buddleia x weyeriana).
I would really recommend taking a pair of clippers to this plant on a regular basis. Cut the whole flowerhead off when there are just a few flowers left. This will greatly extend the flowering season of this shrub.
If you are looking for a native alternative to Buddleia, then consider a combination of Agastache foeniculum in front of Agastache scrophulariifolia. These plants are of similar height and flower at the same time of the year. Agastache is not as beautiful as Buddleia, but most people are merely looking for a plant to bring in butterflies. In my garden, Agastache is even better than Buddleia in attracting Monarch butterflies and various other insects.
There is a lot to like about Buddleia plants. They attract various different pollinators that we love to see in our garden. Buddleias produce large flowers with a lot of nectar and several species of butterflies are strongly attracted to them. To a lesser extent some other insects may also be attracted to the flowers. Buddleia davidii blooms for an extended period and are easy to grow. They can grow 10 ft high and a little pruning will prevent the lanky look.The best of these larger varieties in my opinion is still pink delight or potters purple, but there are plenty of other colours to chose from.
Your garden space may restrict you to growing compact cultivars, but you should understand that the larger specimens are much more attractive to butterflies. You can compensate for this by planting several smaller specimens in your garden. The Nanho series was quite common in nurseries, but they have smaller flowerheads that make less of an impact. The humdinger series are small enough to be planted in pots and will attract butterflies that happen to be passing by.
The best of the mid range butterfly bushes comes from the English Butterfly Series, which includes Peacock, Purple Emperor and Adonis Blue. They can grow to 8 feet. These three varieties have a compact form with large flower panicles. If you want to go with miniature, you can try Blue Chips, which only grows about two feet high. The breeder claims that the flowers on this cultivar are almost sterile eliminating the need to deadhead.
Other buddleias worth mentioning include Buddleia alternifolia which grows to 15 ft high and blooms intensely for a month in May. It weeps like a willow and blooms on old wood so it must be pruned after flowering. There is also the yellow honeycomb Buddleia x weyeriana which should be treated in exactly the same way as Buddleia davidii.
In Ontario, Buddleia will die back to the ground during winter (although it leaves might survive in southern Ontario in a sheltered microclimate). Cut off any remaining flowerheads in October and then cut it back to about 10 inches in early spring. Even if your plant does make it through the winter, cut it back anyway to maintain good form.