Shrubs in my Tropical Garden

by Fred Moody

Why focus on shrubs? After the semi-shade framework has been achieved with palms and other smaller growing trees, I then set about filling in the understory garden area and although shrubs are not compulsory, they can be added to give depth and scale to the garden as well as highlighting parts of a garden with dramatic foliage, colour and coleustexture. Light coloured foliage can be used to soften busy areas and shrubs can also be used just to hide an unsightly background or soften a harsh corner.  From my experience most of these plants respond to a organically rich loam mix which has a pH of around 6.5 to 7.0 and will retain some moisture but will not stay wet. Ideally they will receive a good annual dressing of rotted animal manure in spring and summer followed by a thick application of mulch to keep their roots cool. They need to be well watered during the summer months and kept on the dry side during winter to prevent roots from freezing.

Most of these plants require protection from the hot midday to the early afternoon sun in summer, but (ideally) be sun drenched in winter, that is, they will perform best in a Northerly facing position.  Let me start with the common Coleus (Plectranthus scuttellaroides hybrids). These plants once considered annuals and house plants make inexpensive, easy care, colourful highlighters for shady conditions. Their roots must be kept cool in summer to prevent wilting of their large colourful leaves. I have an excellent display of these plants and the secret to their maintenance is inFijian Fire Plant pruning regularly to the desired height and to continually pinch out emerging flower spikes, thus preventing the plants from going to seed and becoming tall and spindly.

Coleus are members of the Lamiaceae family which includes many of our culinary herbs but also includes the genus Clerodendrum which has many shrubs with garden potential for the Sub-Tropical zones. Look for nursery plants bearing the 'Stained Glass Window Collection' label.The most commonly question asked was, "Why don't crotons (Codiaeum variegatum) grow in the Sydney garden?". The answer is that most will if you give them the growing conditions that they prefer, i.e. protection from the hot summer sun at midday, plenty of light and a preference for morning sun, an organically rich growing medium and plenty of water to get them started (in summer) and withholding the water in winter. Codiaeum are members of the Euphorbiaceae family which also includes Acalypha ( the Fijian Fire plant or red hot cats tail), Euphorbia milli (crown of thorns) and Euphorbia pulcherrima (poinsettia hybrids).

Acalypha wilkesiana (A. godseffiana in horticulture) and it's many cultivars will thrive in full sun after they are established. These plants will tolerate sandy soil and are moderately drought resistant once established. Leaf colour combinations can range from orange and green to bronze, burgundy and leaves which are green with orange/red margins. Many also have large ruffled leaves whilst others have a cqueen sirikitombination of fancy almost trident like leaves which are ruffled and have serrated leaf margins. Prune in spring and summer to maintain shape and size.                                                                            

My all time favorite shrubs has also been my greatest horticultural challenge here in Sydney and that is to grow the Mussaenda hybrids. 'Queen Sirikit' has greatly enlarged pink sepals with a darker rose edge followed by a much smaller tubular yellow flower, but the draw card is the huge weeping bunches of pink and red somewhat striated sepals which call out "look at me".    

'Donna Luz' is made up of smaller bunches of pink and red somewhat striated sepals. The genus name is thought to have originated from the Malay word 'nusenda' which means beautiful and many of the Asian hybrids are named after well known women of the region. The down side of this genera is that they are deciduous in winter, but this allows for pruning  just prior to the new leaves emerging in spring.                       

In Sydney these plants must be watered frequently on hot days and it is imperative that theyiresine are kept dry over winter. Once again a rich organic medium is necessary for good root growth and a sunny Northerly position is required to get these plants into early spring growth and the grower will be rewarded with flowers from Christmas to March.

Pentas are another sub-shrub of  a bygone era. With there small heads  of  brightly coloured star flowers in reds, pinks, mauve and white, they are generally in the 60cm height range and will reward the grower with masses of flowers. These plants respond well to pruning over the summer months and should be thinned out to reduce fungus disease.

Hibiscus rosa-sinensis (Hawaiian hybrids) are another special group which have stood the test of time and they come in all the colours of the rainbow plus more. These plants grow and flower at their best in full sun and while the flowers generally last but one day, their stunning beauty makes the effort of growing them worthwhile. The major things to consider when growing Hibiscus is that flowering only occurs on new growth therefore an annual pruning in July/August is essential. The later you prune the later it will be before you get flowers.

 mussaenda and coleus

Hibiscus are hungry for a good fertilizer high in potash, and the downside is that some insecticide spraying will be necessary during the flowering season to control the Hibiscus beetle which cause buds to drop off before they open. If getting enough sun is a problem, Abutilon hybrids (the Chinese Lanterns) are a good alternative and these also have a good range of colours but tend to grow taller.

 

Medinilla multiflora is another shrub for bright filtered light areas. Growing to about 1 metre tall, (mine is competing successfully with a large Cyathea tree fern), this plant has rather large leaves that are deeply marked with primary veins. The large infloresence bearing many pinkish flowers appear in spring and when fertilized mature to become purple berries which last for many months.

 

Iresine diffusa variety lindenii, (formerly Iresine lindenii or 'bloodleaf') is another of those plants thajusticiat grow best in bright filtered light. It's burgundy leaves are a good addition to the colour palette to brighten areas that require a lift, however it is not suitable for high wind areas as the stems are not very strong and require constant pruning to maintain their shape.

 

Another beauty is the pink Justicia carnia with its heads of pink flowers. Whilst it will grow in shady areas it performs best in a well lit shaded area and with dead heading of the spent flowers, it can retain a compact shape with constant flowering cycles. Another of this genus is Justicia aurea  with larger flower heads on taller stems.

 

 

Cane type begonias should not be overlooked as a shrub for use in the tropical foliage garden either as many have very attractive leaves and will provide colourful flowers in shades ranging from pink to red and orange for most of the year. There are many other shrubs I am trying such as Vireya (tropical rhododendrons), Calliandra (powder puff bush), Apelandra sinclairiana which has a terminal infloresence with shell like orange bracts from which pink flowers emerge.                                                                                                

Plant Articles Home