For many years now I have been frustrated by how little is known about these fantastic garden plants. Even though they can be found in nurseries all over the UK, very few people have realised the potential of these late season perennials.
The genus Strobilanthes lives in the Acanthus family (Acanthaceae), and is mostly made up of tender plants from tropical regions. There are a few species from colder temperate areas which are ideal plants for gardens in the UK and most of Western Europe.
Strobilanthes wallichii (syn. S. atropurpureus) is possibly the best known of the hardy species, and comes from the Himalayas in Northern India. In the wild it apparently blooms every 12 years, but thankfully it is less shy to bloom in the garden!
The unusual 'gramaphone horn' flowers of Strobilanthes wallichii appear in late summer and continue until the first serious frosts. This bicoloured form (at least I think it's a bicoloured form of S. wallichii instead of it's own species) was given to me by a gardener for the National Trust....
Similar to S. wallichii is Strobilanthes attenuata, which differs mainly in stature- Strobilanthes wallichii is a larger plant whereas S. attenuata is smaller and more compact. The only non-purple flowered hardy species I have come accross is Strobilanthes nutans, a white flowered species from Nepal where it grows as an epiphyte in cloud forests.
Strobilanthes nutans is more of a floppy scrambler than the other hardy Strobilanthes I grow, it probably hangs from trees and rocks in the wild, so needs more support in cultivation. I am happy to let it scramble and flop at the edge of a trough where it can enjoy the kind of open soil that it is used to in the wild. This photograph (above) of S. nutans was taken at RHS Rosemoor where it is allowed to scramble over rocks.
The hardy Strobilanthes seem very easy to grow providing you can get the soil right. In the wild they grow in deciduous woodland and areas of high seasonal rainfall, so a humus rich soil is a must, as is plenty of water during the growing season. In my experience they will take some drought for a few days but will never quite be at their best afterwards. If you are growing Strobilanthes in the ground then leafmould or composted bark will be vital if your soil isn't the perfect 'moist, humus rich and free draining' that so many plants seem to enjoy! If your soil is really not suitable for Stobilanthes then a trough or raised woodland bed would be an excellent place to grow them, as well as being an excellent way to grow Trilliums, Arisaemas etc.
Strobilanthes are very useful in the woodland garden because they flower later in the year than many choice woodlanders, extending the season of interest significantly. While your Trilliums, Epimediums, Arisaemas and other woodlanders are flowering in spring the Strobilanthes are all still only just emerging from dormancy, but then as the spring plants are retreating in late summer the Strobilanthes have grown up and are starting to flower, making effective use of the space!
I have never tried Strobilanthes from seed myself but am told that it is fairly straightforward. Where the soil is very good they can self seed, but seedlings are easy to dig up and plant elsewhere or return to the parent clump.
Although I use Strobilanthes as woodland plants I should mention that I have seen them grown very effectively in open sunny locations, although always in areas with reliable summer rainfall or access to water. Here they seem to flower a little bit more than in shade and make excellent late season border perennials.