Thought I’d share what I’ve learnt so far from research and from experience. Creating a rainforest garden is easy! It just takes time (and a bit of hard work at the beginning).
The secret to creating a rainforest garden is not water. It’s mulch, mulch, and more mulch! In fact, water is no more a necessity for a rainforest garden than it is for any other type of garden but a thick layer of organic mulch is vital.
Ready to be spread.
Before you can even think about planting anything, the soil has to be made ready. Rainforest plants, as a general rule, have very timid shy root that tend to stop dead at the first sign of an obstacle. So the plants simply will not grow in hard ground . They grow best in thoroughly loosened soil. The ideal depth is about 30cm.
The corner we chose for our rainforest had provided access for the trucks and bulldozers while the estate was being developed. There was very little topsoil left and in places the ground was badly compacted. We hired a man with a bobcat and ripper to dig up the area over which we’d spread 20 bags of horse manure, then we covered the entire area with a thick blanket of mulch - about 50 bales of sugarcane trash, plus newspaper, grass clippings and anything we could get hold of.
After a few months we dug the broken down organic matter into the soil, adding lots of blood and bone, and topped it up with another 50 bales sugarcane trash. Each year in spring we repeat this process. Gradually a layer of organically rich soil has begun to develop.
Thick organic mulch is essential for several reasons:
· 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
This is true, of course in all gardens, but especially so with a rainforest. Because rainforest plants are very surface rooted, it is essential to keep the surface of the soil cool and moist, otherwise the roots will bake and dry out.
If weeds or grass are allowed to grow around the base of rainforest plants, they cannot compete so a thick application of mulch will keep weeds at bay.
It is essential that the mulch be organic, since the recycling of nutrients is very important for their growth. It’s best to use materials that will easily break down. If you use woodchip or pinebark, it will rob nitrogen from the soil and you need to add nitrogen rich fertilizer regularly to replace the nitrogen drawdown. In my opinion it’s easier to avoid using it. There are many other things to choose from.
It is also quite important to keep the mulch away from the base of the trunk, particularly in summer when there’s a lot of rain and humidity. The trees can develop collar rot.
Provided there is a thick layer of organic mulch, a rainforest garden doesn’t need any more water than a normal garden, although it loves any extra water it gets.
The plants must be watered for the first few months until they are established. I read somewhere that you should water them daily for the two weeks, then weekly for the next 2 months, so that’s what I did. After that they got whatever water fell from the sky.
Our trees are mainly indigenous to South East Queensland so I believe they should be adapted to the range of weather conditions they encounter here. No one goes into the bush to water the trees and they survive.
So far we haven't lost any trees through lack of water. Some of them struggled for the first couple of years because they weren’t getting as much water as they would have liked, but we were on very strict water restrictions so it was survival of the fittest.
Rainforest plants love to be fed. Fertiliser brings out the lovely foliage colours on new growth.
The rules are the same as for all Australian 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.
When planted, our trees got a mix of liquid seaweed and fish emulsion. Each spring they get a liberal spread of blood and bone and pelletised chook manure when their mulch is topped up. Maybe they would like more fertiliser than we currently give them but while we're not watering them, I'm a bit careful & only feed them when there's a fair chance of rain.
I did quite a bit of research before we started this project. The best book I’ve read on rainforest gardening is "Gardening with Australian Rainforest Plants" by Bailey & Lake. Another great series of books - Australian Rainforest Plants (Books 1- 5) by Nan & Hugh Nicholson. Sites such as http://www.floraforfauna.com.au/ helped us decide the best plants for our region.
We wanted structure to the garden but also a natural feel (so some pattern and repetition of plants along with diversity).
John had propagated about 30 small leafed lilly pilly (Syzygium leuhmannii), 10 Golden Penda (Xanthostemon chrysanthus) about 10 powder puff lilly pillys (S.Wilsonii) from seed. They were tucked away in the greenhouse.
As a ratepayer were allowed 16 plants per year from our local Council. Their plants are beautifully healthy and most are indigenous to our region so this was our favourite source of plants.
We chose a variety of lilly pillys - Bush Cherry (Syzygium paniculatum), Syzygium Aussie Southern and Syzygium paniculate. Also four Pink Euodia (Euodia elleryana), a couple of Illawarra Flame Trees (Brachychriton acerifolius), Tuckeroos (Cupaniopis anacardiodes), Ivory Curls (Buckinghamia celsissima) and a Blue Quandong (Elaeocarpus grandis).
We also bought a few trees that we particularly wanted from a local native plant nursery including a Davidson’s Plum (Davidsonia jerseyana,) Native Frangipani (Hymenosporum flavum), Rose Apple Lilly Pilly (S. Moorei) and Wheel of Fire (Stenocarpus sinuatus). Not all of these are from S.E. Qld but are native.
Planning and planting the rainforest garden
The rainforest area is in the front corner of the yard and is the first thing you see when you drive up to our house. It needed to be attractive from the street, enclosed from the front and side but open and inviting from the centre of the yard.
We used the small leafed lilly pillys as a screening hedge along the side fence – They protect the inner garden from drying winds and provide an enclosed rainforest feeling. We spaced them 1.5m apart and for the first couple of years, trimmed them regularly to encourage thicker growth. For the streetscape we tried to create a layered effect with low growing shrubs and clumping plants in front of taller bushy trees. Trees with different seasonal flowering were chosen where possible to provide interest for most of the year. Dianella species were planted to create a front border.
In the centre the trees are taller and further apart. The plan is to fill the area with shade-loving understorey plants.
The entire area is on a slope and we discovered during our first heavy downpour of rain (some two years after we’d planted) that mulch does not prevent erosion. Although we had created a lovely top layer of cultivated organically improved soil, it was sitting on shale and while the mulch stayed put, the soil turned to mud and flowed down the slope with run-off from the heavy rain. We lost a couple of trees before we realized what was happening. They survived the drought, then had the soil washed out from under them when it rained. We added rock and log features which serve to slow or divert the flow of water.