Living in a hot, subtropical climate means that I feel a great need for shade in my garden. Our summers can be very long, hot and humid so the shade gives welcome relief not just for me but for the plants as well. I tend to find that many plants that might be considered as full sun in cooler climates prefer some shade here.
Even in the shade, I want to grow flowers. A few years ago information about flowers that would grow and flower well in shady spots was very limited. The adage was and to a large extent still is; flowers like sun. As I started to find more and more plants that did indeed flower, and flower very well, in shady places, I also started to realise that many of them belonged to the same plant family – the Acanthaceae.
A huge delight to me has been getting to know and grow more of the plants in the Acanthaceae family. This is a very large family, which are mostly tropical and sub-tropical in origin and which includes an enormous wealth of plants which flower fantastically well. Most gardeners are reasonably familiar with the bears britches, (Acanthus mollis), and the polka dot plants (Hypoestes) and probably some of the Justicia which are part of this family, but beyond these few, other members of the family remain hard to find in nurseries.This is a great shame, as there are so many wonderful garden plants in this family. It is also a shame that we are missing the opportunity to grow more flowers in the shade. With our long and very hot summers in the tropics and sub-tropics, and even in some of the warm temperate areas, having some shade is critical, but I for one, and the bees for two, would like to have the shade and the flowers too.
Many of these plants will grow well in any frost free position. In cooler climates they will be happy with a little more sun, so may not flower as well in the shade in cool climates, but will certainly make great pot plants for warm verandahs or conservatories.
Currently the biggest difficulty with growing a selection of the Acanthaceae is finding them. You may need to seek them out from collectors, garden clubs or small independent plants people. Many grow quite readily from cuttings or seed.
In the right conditions – being a shady sub-tropical garden, these plants can be very hardy, having little trouble with pests and diseases and needing only some occasional pruning or deadheading to keep them neat. Some however do too well and have weed potential, so as with nearly all plant groups, watch out for those that may be overly aggressive and keep them in their place.
Let me introduce you to some of the Acanthaceae family which I am lucky enough to have growing in my sub-tropical garden. You too might just fall in love with their often bright colours and bold flowers that can add drama to any garden. I have approximately 40 different species across 17 genera, so I will give you a taste with 10 of my favourites.
1. Brazilian plume flower in pink or white (Justicia carnea) is one of my favourites, and is a wonderful large flower sometimes called flamingo flower as the little pink calyxes resemble a whole bunch of flamingo heads. It repeat flowers through late summer and autumn, even in fairly dense shade under trees, and is very easy to strike from cuttings. I have other Justicia also making colourful statements in shady areas of the garden, so I need to move on before this article is only about justicias.
2. Chocolate plant (Pseuderanthermum alatum) is so named for the lovely brown coloured leaves with silver streaks. This is a low growing plant which makes a wonderfully interesting plant around the edge of a shady garden. It dies away completely in winter only to return as the weather warms up, flowering all summer long with a delightful spike of little bright purple flowers, and it self-seeds readily.
3. Chinese rain bells (Strobilanthes hamiltoniana, formerly Strobilanthes flaccidifolius), or sometimes known as Darwin rain bells or just rain bells. I know of people who grow this happily in full sun, mine however is growing in dappled light for summer and dense shade for winter, and thriving. It is approximately 1.5 m tall and in late autumn bursts into masses of pink bell-shaped flowers. Just when you think it has finished flowering and go to cut it back, another flush of flowers often arrives. It can get a bit leggy so a good annual haircut not only helps to thicken it up but also provides great cutting material.
4. Trailing velvet plant (Ruellia makoyana) is one of those plants that I couldn’t help falling in love with at first sight! Deep green leaves with purple underside and white veins and brilliant pink trumpet shaped flowers. It loves dry shade but when backlit by soft dappled light it glows brilliantly. All the ruellias thrive in dry shade and add a riot of colour to dull spots in the garden. This one tends to be somewhat restrained in growth habit, but not in colour brilliance.
5. I have a bright chartreuse hypoestes (species unknown) which flowers en mass in late autumn in deep shade. It self-seeds readily, but is easy to pull out and is worth it for the show of vivid colour it puts on reliably each year. While there is nothing remarkable about this particular plant during summer, except the large green leaves filling dry, dark corners of the garden, when it suddenly bursts into flower in autumn it is a show stopper with the mass of colour where it is not expected.
6. Fire spike (Odontonema cuspidatum) is an old fashioned plant that the nurseries may have forgotten about but gardeners certainly haven’t. It provides tall spikes of brilliant red flowers in shady spots with absolute neglect. The plant is unassuming and often unnoticed until it suddenly bursts into flower.
7. King’s Mantle thunbergia (Thunbergia erecta) will happily provide royal purple blooms in part shade (yes, a relative of the old ‘black-eyed Susan’ vine). It can be trained as a vine, or trimmed as a shrub. It is very long flowering, and mine rarely is without a flower, even though it is usually rather smothered by other taller growing plants nearby.
8. The delightful yellow and white birthday candles (Pachystachys lutea) will flower in shade and can make a great statement plant in cottage gardens or in tropical gardens. It will take a fair bit of sun but will be happier in dappled shade, and will grow well under trees with some supplementary watering.
9. Brazilian red cloak (Megaskepasma erythrochlamys) is a large shrub that will flower well in sun or shade, with masses of big, dark-red blooms. It is hard to miss in flower and, being fast growing, makes a good dense informal privacy hedge. It too can be pruned as hard as you like and will only thank you for it – and reward you with cutting material. The large leaves can wilt a little if grown in the sun but it is surprisingly hardy and dry tolerant, as well as perfectly happy with wet conditions.
10. And who could miss the giant sage (Brillantaisia nyanzarum) when in flower with its massive leaves and giant spikes of purple flowers? This one can get huge, with massive flower spikes, so can be a real statement plant. I have recently used a handful of prunings and shoved them straight into heavy clay soil to make an informal hedge near the back of a client’s home. All the cuttings took and are now on their way to putting on a dramatic show which they will be able to enjoy from their elevated deck. Mine gets full, deep-winter shade and plenty of summer sun. It gets waterlogged and extremely dry and seems to cope with everything. Dropping a tree on it didn’t phase it at all – it simply grew back denser than before in no time at all.
I find all of these plants both hardy and reliable in rather unreliable conditions. I have heavy clay soil that tends to waterlog. It can get very dry as I forget to water, and yet these plants have all powered on in my garden and continue to impress me with masses of flowers in the shade. Use this list as a very brief introduction and leap into the world of the Acanthaceae if you are at all interested in a warm climate garden with year-round flowers in the shade.