Garden Pyramid

Clive Blazey explains the Diggers guide — our Garden Pyramid

Australians are still largely ignorant about the importance that trees play in our lives.

We live on the oldest continent with the poorest soils and the driest climate which certainly will become unbearably hotter in just one or two generations.

We wood chip our old growth forests and export these magnificent prehistoric trees, which get turned into ephemeral packing materials just for the consumer society. In Queensland we allow farmers to destroy forests for farmland, which is an even greater contributor to the build-up of CO2 than coal-fired power stations. We led the world in putting a price on carbon and then stupidly overturned it.

In just 220 years we have cut down almost half our forested areas when other countries have taken 3000-4000 years. But worse still, we started with a poor inheritance and we ignored the warnings. When will we ever learn?

Recently our obsession with house renovations has seen the absurd idea promoted by ‘Tradie Celebs’ that in our backyards we should give up on grass and trees and just have paving and flax. In fact you can now replace living grass and use artificial turf which tests show raises backyard temperature to between 50-60°C. Have you ever listened to more stupid advice?

Choosing the right shade trees

The most important decision a gardener can make is to choose the right trees to cool their garden. Trees and grasses expel water through their stomata on hot days, providing rain in forested areas and a 10-15°C temperature buffer in gardens during 40°C heatwaves.

So in our Heronswood garden, we sit in the shade at a pleasant 25°C rather than 40°C.

To help you choose your trees we have provided horizontal spread information, so you can avoid planting trees too closely or choosing trees that provide lousy shade, such as eucalypts.

Trees and lawn: 50% of garden area

Now the big question is how much of your garden should be shaded by trees and how much should be evaporatively cooled by grass? Until your trees and lawns provide at least 50% of their area with shade then, in our experience, it will still be unpleasant to be outside in summer.

Whether trees take half of that area, i.e. 25% of that total or 40% of that total is a matter of personal choice. Once planted, trees require the least effort and lawns the most.

There are lots of other reasons to provide this sized area for trees without resorting to planting gigantic oaks that may limit your choices of other trees.

Trees have deeper root systems to survive dry periods so they need perhaps half the water needed to grow vegetables and fruit. The shade they provide means the area for weekly mowing of grass is halved. They are a habitat for birds and soil bacteria which build soil fertility and reduce your need for artificial watering, not to mention with deciduous trees the leaves provide nutrients every winter.

If, instead of having a small garden of say 200-500 square metres (e.g. 10 metres wide by 20-50 metres deep), you had a whole hectare e.g. 100 x 100 metres), then the tree and grass planted area would increase to 94% because otherwise the area left for the labour intensive growing of flowers, shrubs and food would then require 2-3 full time gardeners.

Old Desert Ash provides the shade of 17 ornamental pears!

Flowers and food: No more than 50-100 square metres of space

Fast growing flowers, fruit and vegetables must have full sun to grow and mature well free from the shade of nearby trees. Just 50m2 of space is all that two people need to be self sufficient in vegetables and fruit and 30-50m2 is a big enough area to create a beautiful summer flower garden.

These two areas are the most gardening intensive areas, needing digging, sowing, weeding and pruning, so it is vital to keep this area small enough to always be ahead of weeding. Hence in a very large garden of a hectare then this area would not expand beyond 200-500m2 leaving 94% of the area for tree planting or extensive shrubberies or rose gardens.

Why so few native trees chosen?

Eucalypts are the most inflammable trees and they provide only 20% shade canopy because their leaves hang down. Our rainforest trees make far better choices because they have lush green foliage, are used to dry periods of 6 months a year and, of course, have adapted in the botanic gardens in Adelaide, Melbourne, Sydney and Brisbane where 150-year-old specimens are thriving.

At our Heronswood garden, 70% of our trees are from Australia's rainforests rather than our dry plains, and their water-holding leaves protect gardens from bushfires.

A note on ornamental pears

Recently councils have been planting pears, which have beautiful spring blossoms but rather upright habits. This might suit tiny spaces but they are a poor choice because you need so many in moderate to large gardens.

We have a Desert Ash that spreads 25 metres across and half this tree will shade over 200 people for weddings. To shade this same area would require the planting of over 17 ornamental pears.

More

Choosing Beautiful, Edible Plants

Bernadette Brady talks about creating art with vegetables at Heronswood

Gardening with Flowers

Choosing the best Diggers selections for the cutting garden

Grow Your Own Berries

Tim Sansom gives his tips on pruning and training for success with your cane fruit crop

Grow Your Own Food (Early Summer)

Bernadette Brady helps you start growing your own food in just 1-3 weeks

Grow Your Own Organically

Bernadette Brady explains how we make 'weed tea', control pests and serve organic food in our restaurants

How to drought proof your garden

How to drought proof your garden

Moon Planting

St Erth's head gardener Julian Blackhirst explains the lunar planting cycle

Plant Ratios for the Backyard

Clive Blazey's thoughts on providing the right balance of plants in your backyard

Q&A - Green Manures

Trials manager Ian Magnus answers questions about using green manures to boost soil fertility and water retention

Q&A - Mulch

Bill Bampton, head gardener at Heronswood, explains our success with making and using mulch

Q&A - Seeds

Seed manager Evette Jungwirth answers your questions about growing from seed successfully

Q&A - Soils

Hugh Hunkin answers your questions about soils and why they are at the root of most gardening problems

Soft green succulents for a lush green garden

Bill Bampton transforms Heronswood’s gravel garden

Spring Gardening

Bernadette Brady recommends getting your hands dirty with some tasks in the spring garden

Subtropical Growing Zone

Tim Sansom explains the heat generated by “Hot Zone” discussions

The “Hauteculture” of Espalier

Bill Bampton talks about turning an untidy orchard into a bountiful border

The best flower selections for ‘This goes with that’ summer borders

Clive Blazey, author of ‘The Complete Guide to the Flower Garden’, discusses the power of intelligent combination

Tomato Growing Problems

Caromy MacDougall explains some common tomato growing problems and how to minimise them

Veganics and plant-based living

Plant-based living launches Veganics The vegan movement is gathering momentum for many reasons from animal welfare to climate change, and this is creating a wave of change across all industries from wine, to clothing and even gardening.

Related Authors

Clive Blazey

Clive is the founder of The Diggers Club, a pioneer in the rescue of heirloom vegetable and fruit varieties and author of seven books on flower, vegetable and fruit gardening.

Related Magazine

Winter Garden 2016

Choosing the right trees for your garden plus potatoes, berries, grapes and heirloom fruit
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