Creating a Rainforest Garden with Australian Tropical Plants

This article is extracted form the Yuruga Newsletter
Vol 12 No 1
(January 2004).

The focus of this article is for gardeners in tropical Australia.
However, the basic principles apply for throughout Australia
with minor modifications for local conditions.

Creating a rainforest garden is easy!

There are two secrets to creating a rainforest garden, and no, they are not water, and more water! In fact, water is no more a necessity for a rainforest garden than it is for any other type of garden.

The two secrets are:

  1. Dig up the garden bed thoroughly to provide as much loose soil as possible;
  2. Provide a thick layer of organic mulch.

Soil Preparation

Rainforest plants, as a general rule, have very timid root systems. Unlike acacias, eucalypts and grevilleas which have robust root systems capable of penetrating hard ground, rainforest plants have timid, shy root systems that tend to stop dead at the first sign of an obstacle. Consequently, rainforest plants planted in hard ground simply will not grow.

Rainforest plants grow best when you garden in the traditional fashion – pretend they’re roses or a vegetable garden, and plant them in a bed of thoroughly loosened soil. The ideal depth is about a foot (30cm). On a small block of land, this means rolling up your sleeves and getting stuck into the ground with the pick, shovel and elbow grease to physically break up the soil. You haven’t finished until your original hard lumpy ground is nice and soft and friable.

If you are planting a large garden, it’s well worthwhile to use a machine – a bobcat or backhoe, or even a small bulldozer with rippers can prepare a large garden bed in a flash. It’s not expensive – for less than one hundred dollars you can prepare a garden bed which would take many days to prepare by hand, and the resulting plant growth will be spectacular to say the least. (See Information Sheet ‘Soil Preparation’)

Mulch

Mulch is absolutely essential to grow rainforest plants well. The mulch should be organic and applied as a thick insulating layer on top of the soil much like a blanket covering a bed.

Thick organic mulch is essential for several reason, including:

  • It keeps the soil moist by reducing evaporation
  • It controls weed growth
  • It keeps the soil cool
  • It provides a source of recycled nutrients
  • It keeps the soil healthy by maintaining a balanced population of micro-organisms

Unlike most acacias, eucalypts and grevilleas, rainforest plants are very surface rooted. It is therefore essential to keep the surface of the soil cool and moist, otherwise the roots will bake and dry out.

As we said above, rainforest plants have timid roots; give them an obstacle and they give up very easily. If you allow weeds or grass to grow around the base of rainforest plants, they cannot compete.

Weeds and grass will severely inhibit the growth of rainforest plants. A thick application of mulch will keep weeds and grass at bay.

For rainforest plants, it is essential that the mulch be organic, since the recycling of nutrients is very important for their growth.
The type of mulch you choose is not important, so long as it is organic. You can use anything, so long as it was once a plant. In north Queensland, bales of mulching hay are popular. In some areas, peanut shell may be available. Many shire councils sell mulched-up garden waste. Wood chip is fine. Newspapers and cardboard are OK, but it is best to shred them first – if you spread them out in sheets they act as a thatched roof and prevent water penetrating the soil beneath. (See Information Sheet ‘Mulching Your Native Plants’).

Mulch should be applied as a clean blanket on top of the soil surface. It should never be dug into the soil – this is for compost, not mulch.

Things such as black plastic are no substitute for organic mulch. Black plastic does not allow the soil to breathe, and it does not allow the recycling of nutrients that is so important. In warm climates, it can cause the soil to overheat. Don’t use black plastic. If you really think you need to, don’t. Make your layer of organic mulch twice as thick instead.

Watering/humidity

Provided you have a thick layer of organic mulch, you will find that you don’t need to water your rainforest garden any more than a normal garden, although it will love any extra water you can give it. Of course, your rainforest plants must be watered for the first few months until they are established, just like any plant, be it a wattle, grevillea or callistemon. (See Information Sheet ‘Watering Your Native Plants’).

However, rainforest plants as a rule cannot tolerate dry winds. Unlike acacias and eucalypts etc., which have a thick waxy cuticle over their leaves (among other adaptations) to prevent excessive moisture loss in dry times, rainforest plants have little protection against evaporation since they have had no need for it in their natural habitat. It is more important to maintain a reasonable humidity level in the air than it is to apply water to the roots.

To grow some of the more delicate species in drier areas such as Townsville or Mt Garnet, you may need to trap humidity around your plants by planting a shelter belt of hardier species or by creating a courtyard.

Fertiliser

Rainforest plants love to be fertilised – fertiliser brings out the lovely foliage colours that make rainforest plants such a delight to grow.

The rules for fertilising rainforest plants are the same as for ordinary natives – check the N:P:K ratio to make sure the phosphorus is low – less than 3% is best.

Water in well, and don’t overdo it. Like medicine, a little is good for you, an overdose can easily kill. (See Information Sheet ‘Fertilising Native Plants’).

A handy reference to rainforest plants for your garden:
Growing Australian Tropical Plants‘ by Radke & Sankowsky

Let’s dispel some of the common myths …

Myth : Rainforest plants need to be planted in the shade.

Wrong! Just because the rainforest is a shady place to walk in, does not mean that rainforest plants need shade. What it means is that rainforest plants cast shade. In fact, if you walk through the rainforest you will notice that the seedlings on the floor of the forest in the dense shade are not growing – they are sitting in a dormant state waiting for a gap to form in the canopy so that the sunlight can stream in. It is only when they receive full sunlight that they start growing.

If you plant your rainforest plants in the shade, they will grow slowly, and they will become thin and lanky as they struggle upwards to the light.

Rainforest plants can, and should, be planted in the full sun, where they will grow thick and bushy and flower young. In their natural habitat, most rainforest plants do not flower until their canopy is in the sun. By planting them in the full sun from the start, you will trick them into believing they are already at the top of the canopy.

Of course, this does not apply to the shade dwelling understorey shrubs of the rainforest – these naturally need the shade – so use your commonsense!

Myth : Rainforest plants are too large for ordinary gardens.

Wrong! Most rainforest plants grow in the garden to only about a quarter or a third of their height in the forest. By planting them in the full sun from the start, they have no need to grow taller and taller to reach the sunlight, since they think they are at the top of the canopy already. I wonder how many of you have an Ivory Curl (Buckinghamia celsissima) or Golden Penda (Xanthostemon chrysanthus) in your gardens? Would you have planted them if you had known that they are rainforest trees from north Queensland, where they commonly grow 20-30 metres tall in the forest? In cultivation, however, they are rounded shrubs of only about 5-8 metres, and this is true of most rainforest plants, with the exception of plants such as the Kauri Pine and Bunya Pine.

Myth : Rainforest plants should be planted under a canopy of existing trees.

Wrong! Plants planted close to existing trees generally do poorly due to root competition and lack of sunlight. Take the plunge, and plant your rainforest trees in the sun from the start. Most of our rainforest plants for sale are in the full sun in the nursery, so don’t be afraid to plant them in the sun in your garden.

Myth : Rare plants are difficult to grow.

Wrong! Some rare plants are quite hard to grow, but many are surprisingly tough and hardy. Rarity is often more related to habitat isolation, than to any intrinsic feature of the plant itself.

Myth : Rainforest plants can only be grown in soil that matches the soil type in the wild.

Wrong! Rainforest plants can be grown in almost any type of soil. Mulch and loose soil are the main requirements; fertilise if necessary.

Planning your rainforest garden

To create an attractive rainforest garden that is pleasing to the eye, you need to use a fair proportion of hardy, bushy species that will give the garden its basic structure, bulk and backbone. There are many species that fit this bill, but some examples are the hardier, tougher Syzygiums and Acmenas, and plants like Flacourtia, Scolopia and Xanthostemon.
Pay special attention to the plants that you place on the edge – these are the ones that hit you in the eye every time you look at your garden. On the edge, you should place the plants that have an attractive shape, attractive foliage or spectacular flowers and the plants that could be smothered if placed in the middle of the garden.

Leggy plants are best in the middle.

Your garden should include where possible plants for birds and butterflies, flowers and fruits. The Yuruga Information Sheets ‘Attracting Birds’ and ‘Attracting Butterflies’ give you more information.

Having taken this approach, then you can start placing the more unusual plants that have specific requirements in and amongst this basic backbone.

Happy Gardening!

3 Replies to “Creating a Rainforest Garden with Australian Tropical Plants”

  1. I just wanted to thank you for taking the trouble to explain so clearly how and why it is a good idea to use some of these plants which may be considered to be unusual. Personally I use every excuse I can to include these exotic tropical types in my garden designs,sometimes it is so difficult to find the actual plants,though.

    1. Hi Victoria,

      Thanks for your comments. If you look through our stock list on the website hopefully you will find many of the plants you are looking for. We update it every month, so it’s worth checking regularly.

      Regards,
      Andrew

  2. Hey that was a great write up on preparing your garden for rain forest plants. This is a must read for anyone thinking of choosing this kind of landscape.

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