Dry subtropical plants are well suited to Sydney’s climate however many people tend to shy away from planting them as they don’t fit into any particular box when it comes to maintaining them. With the correct soil conditions and climate this versatile group of plants are on the lower end of the maintenance scale. They just need a more delicate hand and a slightly different approach to other perennials and shrubs.
Dry subtropics plants you may need to manage in your garden include bromeliads, Dyckia, air plants (Tillandsia), Alcantarea, Euphorbia species, Sansevieria (mother-in-law’s tongue), Aloe species and cultivars, Epiphyllum (orchid cactus), and Rhipsalis.
First, leave your pruning shears and hedge trimmers in the garden shed. These types of tools are not needed when maintaining many subtropical plants. Instead, you will need a:
Maintaining subtropical plants isn’t as clear cut as most people would like. As the gardener/designer, you need to define an area you want each of the different plant types to fill and, as many of these plants have spreading habits, you need to ensure that while they have space, you also control their borders. Each plant should have its own section to shine without another invading its territory, as each of these subtropical plants makes a strong individual statement with colour, form or leaf texture, which is ruined when they become jumbled up together instead of in defined blocks.
Also, some dry subtropical plants are succulent shrubs and, like all shrubs, they might need to be pruned for a bit of shaping or to bring back lower foliage. However, their super-thick, often thorn-covered stems, which might also exude a milky sap when cut can intimidate gardeners into leaving them well alone, so they don’t look as good as they could.
Although dry subtropical plants are low maintenance plants, they’re not ‘no maintenance’ plants and need regular decongesting, lifting and dividing, trimming and pruning to keep them looking their best. Here are some ways you can manage your dry subtropics plants. You can click on any of the photos to see a larger version for close-up detail.
1. Bromeliads: There are many members of the bromeliad family that will give a garden a wide variety of leaf colour, flowers and foliage texture. Bromeliads may be epiphytic or terrestrial. They can be found growing in a range of conditions from rainforests to exposed rocky crevices on cliff faces or they may make their homes in branches of trees. Most often those growing at ground level will have thorns on their leaf edges for protection. Bromeliads grow as single rosettes, and they have rhizomatous roots that produce new plants or pups.
Due to the circular leaf arrangement they are able to direct water to their leaf bases where they hold water in what is called a tank or a vessel. When watering it is best to keep water in this well and any additional water that may spill over may be sufficient to water the roots.
Many of the new baby plants, or pups, will spread out from the parent plant, and some may even grow over the top of others. These new plants can easily be lifted and divided. Sometimes it may be better to lift the whole clump, divide it up and then replant. These plants can be divided by simply cutting the rhizome stem with a sharp pair of secateurs. They can then be replanted into a well-draining mix. Make sure the base of the rosette is right at the soil surface to ensure that the water will drain away.
After flowering, a bromeliad will die but normally by that time new pups have shot at their base. These new plants will grow to fill the void left by the dead parent plant.
2. Dyckia spp – Dyckia have interesting colour combinations of foliage that seem to become more intense in the cooler weather. They (unlike many bromeliads) can also withstand some frosty conditions. When they do flower, the flower stems can be so long and heavy that shallow rooted plants can sometimes fall over or even fall out of the soil. They may need propping so you can see the full beauty of the flowers. Due to their low water requirements and shallow roots they make ideal potted specimens for pots that are undercover, or are hard to reach with the hose.
3. Tillandsia spp – air plants will absorb water and nutrients through scales on their leaves. These need little to no soil for them to thrive; they only need some type of structure to give them an anchorage point and /or support around which they can wrap their roots, which can attach to timber or even stone. If they are planted too deeply they will rot. They can have a rambling habit, even sometimes growing over the top of each other.
4. Alcantarea spp – These giants of the bromeliad family are normally grown as single specimens for their architectural shape. Some species will reach 1.3-1.4 metres in height and width (4-5ft) with flower spikes towering above the plant at over 2 metres (7ft). Some even have fragrant flowers. They can tolerate full sun to shade, are drought tolerant and can take a little frost. They have a waxy powder on the undersides of their leaves that helps them absorb moisture.
Trimming away old leaves at the base will often improve their appearance. Some say these should only be removed when they tear away easily, but you can also cut them with secateurs.
Like all bromeliads, the original parent plant will die after flowering, leaving anything from one or two pups to dozens at its base. This feature of the plant can be a problem, as you lose the dominant architectural effect of the original plant. The best solution is to lift the entire clump, select one of the larger, strong, and sturdy-looking pups to grow on as a replacement feature plant, and then to find homes for the other offspring. As Alcantarea are usually pretty expensive plants, you should have no shortage of takers!
5. Sansevieria spp, or mother-in-law’s tongue as they are more commonly known, grow well both in the ground or in pots. Sansevieria is a succulent-leafed upright growing plant with sword-like leaves which usually have some level of variegation, in shades of green or possibly banded with cream-coloured edges.
They grow in clumps or stands as they have spreading rhizomes and will spread out as far as they can go, but I wouldn’t consider them invasive as they are not fast growing and they are easily removed. However, as they spread, an empty section can develop in the middle. The new plants want to grow out to where the conditions are more spacious and probably where there is more water and light. This then causes a bare hole to form in the centre of the clump. Sydney landscape designer Peter Nixon calls this the ‘Donut Effect’.
If a few plants are popping up where they are not required or you need to move them back to fill in an empty spot, it is as simple as digging around with a small spade to uncover the direction of the roots, as normally they are quite shallow rooted. Then with a sharp knife, cut the rhizome back to the parent plant and lift out the young plant. It is best to do this in late summer or autumn. If you think there are too many plants or if the plant is growing in a pot it will be easier to lift the entire clump and then divide the whole plant.
Replanting the cuttings is simple and the plants are most forgiving as long as they don’t get too wet. The text books tell you to allow the divisions to sit out of the soil to dry out and callous over for a few days. I have to admit in Sydney I have never done this – normally I just plant them into a well-draining mix and give them a splash of water a few weeks after planting out.
6. Aloe spp and cultivars – with spectacular showy blooms in autumn and winter that attract birds, aloes will survive in full westerly sun and are drought tolerant – can a plant tick any more boxes?
This genus of succulents range from low, clumping forms to shrubs, right up to tree forms. The lower growing species will bulk out and grow into more rounded mounds. The taller growing forms will develop a trunk and become quite sculptural in their habit. These will grow from both leaf and stem cuttings.
Aloe can develop many small pups at the base which you can remove if it looks too congested or so you will have new plants to spread around the garden.
7. Epiphyllum, commonly known as orchid cactus or moon flower is native to Central America and is grown for its spill-over habit that can shower over walls or from hanging baskets. Its spectacular flowers tend to open for the first time in the evening and, although they are short lived, they are a sight to be seen. The heavy stems and succulent leaves can be easily bruised, so cut back any damaged foliage to the nearest stem.
The sprawling habit of these plants needs to be given space so that you can appreciate its true form. It is easily propagated by either leaf or stem cuttings. Using a sharp pruning saw or knife you can cut mature leaves back at the main stem or you can also cut off an entire stem. Ideally these should be at least 15cm – 20 cm (6-8 inches) in length.
Leave these cuttings in a cool dry place to cure and callous over. This may take a few weeks. You can then plant these stems upright into pots. Depending on the width of the pot you can plant numerous plants per pot. Most importantly make sure it is deep enough to hold these cuttings so that the pot does not become top heavy.
Use a mixture of 1 part well-draining potting mixture to 2 parts orchid growing mix. It is best to give the plant very limited water while they are starting to root out otherwise they may rot. Once the plants are rooted they can be lifted and planted out in their new location.
8. Euphorbia – what an amazing array of contrasting plant species sit in this genera. One thing they do have in common is the milky sap or latex which flows from their stems when broken. This is a warning to all gardeners – avoid getting this sap on your skin or anywhere near your eyes as it is highly toxic and will irritant skin and eyes. It can cause rashes.
Euphorbia milii – Crown of thorns is aptly named, as it does have thorny silvery green stems. There are many cultivars available such as Poysean Euphorbia that has bunches of flowers in a wide variety of vibrant colours. Like all shrubs they can develop bare, leafless stems which you might want to prune back to encourage a more leafy look.
Euphorbia trigonia – Another spiky plant, this cactus-like species can be used as a feature plant in the ground or in a pot. Older specimens might need staking as they become more branched, which can cause them to tip over in light soils.
Euphorbia tirucalli – this plant has highly poisonous stems which when cut exude a smell which isn’t very pleasant and can even irritate eyes without direct contact. A succulent, stemmed, tree-like plant, it will grow in a thicket type arrangement. Ideally it is best to use this plant in a section of the garden where it can happily grow and does not need to be maintained in any way.
All of these plants will grow from a stem cutting. It is best to allow the stems to callous over before planting out these plants. This means leaving them in a dry place for a week or two until the cut stem has properly dried out.
9. Rhipsalis – this epiphytic cactus has a pendulous habit with tiny, jointed branches. They are normally found growing in tree forks, however they work well as a thick ground cover, as a spill-over plant or they can create a stunning curtain effect in a hanging basket.
They are easily propagated by taking a stem cutting and planting into a free-draining potting mix or garden soil.