When Amanda Sinclair and Sam Cramer moved into their south Hobart home in 2017, they wanted to turn their giant lawn into a food forest.
But first they had one big, heavy, dense hurdle to overcome: clay.
After discovering clay soil through most of their yard, the couple had to carefully consider how they would proceed with planting their garden.
This is how they turned their hard clay ground into rich life-bearing soils, along with tips from a soil scientist.
Clay soil can be a blessing in disguise
Finding clay rich soils might seem like a bad sign for a new garden but they can be “quite a treasure,” according to Theresa Chapman, a soil scientist and PhD candidate at the University of Tasmania.
This means clay soils can be a great starting point for a garden, but if left to their own devices, they do tend to become “hard and tight”.
Before Amanda and Sam started this gardening project, their experience was limited to some small-scale “pottering in rentals”.
The first addition to their new garden was fruit trees, also their first time planting them. Amanda is a scientist who has studied plants and says “my plant science knowledge was a leg up”.
They sprinkled a mineral called gypsum to the bottom of each hole they dug for the trees to help break up the clay.
Gypsum can be very useful, says soil scientist Theresa, but it is always worth checking where it came from and whether it is sustainable.
After sprinkling gypsum, the couple “added lots of compost” to the holes, says Sam.
Amanda adds that they mixed the compost with broken up clods of clay to achieve about a 50:50 mix, the whole process felt like “mixing a potion,” she says.
Adding lots of compost to their garden was a great idea, according to Theresa.
Compost does not permanently contribute to the garden’s health, but it is “an inoculation of soil biology,” she says.
Having a diversity of living things in the soil, such as soil microbes and worms is key to a healthy garden.
Let the plants do the work
Once they had planted their trees, Amanda and Sam added an understorey of smaller plants.
To prepare the soil for these smaller plants they scraped the grass off the soil, added a light layer of compost, a layer of cardboard to suppress weeds, and topped it off with some mulch.
They then made little holes in the cardboard and planted strawberries, chillies, herbs, and lots more.
The tough roots of these smaller plants have spent the last few years doing the hard work of breaking the clay up for Amanda and Sam.
Theresa endorses this strategy.
“You have to do whatever it takes to get as many plant roots growing through the soil as you can,” she says.
Growing a diversity of plants, like Amanda and Sam are, is important to attract the diverse organisms you need for healthy soils.
While many plants will do the trick, Theresa is a strong advocate for throwing tillage radish in the mix.
“It’s so good at punching down through compacted clay with that big, long tap root,” she says.
Improving the soil with the power of small plants and shrubs has been “a gradual process,” admits Amanda.
The slow work of thousands of roots working the soil over time has paid off.
Amanda and Sam’s young fruit trees are growing fast and the shrubs and ground cover beneath them are bursting with life.
How about veggie beds?
The couple are proud of how the orchard is doing, but when it came to their veggie beds, they wanted instant results.
“We brought in soil for them,” Amanda says.
For anyone wanting their veggies from the garden quickly, bringing in soil and compost is probably the best way to go about it, says Theresa.
You can turn clay intro a productive veggie patch by planting a mixed cover crop of soil improving plants, but it takes time.
Theresa emphasises that good soil comes from a diversity of plants working the soil and recommends nitrogen fixing legumes, fibrous rooted grasses, and plants with large tap roots like her beloved tillage radish.
“But we’re talking quite a few years realistically.”
Zoe Kean is a science writer and communicator based in lutruwita/Tasmania. She loves living things and has a small but blooming garden.
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