A little topsoil is the perfect ingredient

By Nelson Lebo

Alongside the passive solar renovation of our 100-year-old villa in Castlecliff, we also "renovated" our section from a weed-infested food desert to a thriving food oasis.

Starting with sand, couch grass, kikuyu, convolvulus, and pampas lily of the valley, the process of transformation has been slow, but steady. Now that we are midway through our third summer, the property has reached a level of lushness and productivity that gives a feeling of satisfaction - especially when tucking into a big bowl of fresh strawberries.

We were able to achieve these results using much of the same thinking that has provided us with a power bill in the low double-digits. This "eco-thrifty thinking" - similar in many ways to the concept of permaculture - aims for low input and high performance, based upon a solid foundational structure. For the villa, this meant significant investments in insulation, solar hot water, and additional glazing on the north side. For the gardens, this meant investments in wind protection, topsoil, and compost.

All of these investments in sustainable infrastructure serve as prerequisites for long-term high-performance. For the villa, high-performance is measured by thermal comfort and low power bills.

For the gardens, high-performance is measured in plentiful, healthy kai. All of these investments can also be measured by payback period - a concept highlighted over the last three weeks of this column.

Without wind protection and a small amount of topsoil, I reckon growing fruit and veg one street behind Seafront Road would be a constant struggle.

People in these parts say "sand eats compost."

By this, they mean that compost quickly decomposes and leaches through the porous sand, leaving little nutrition. A top dressing of topsoil, however, binds compost where it can be reached by plants' roots. Topsoil is also better at retaining water than sand. Our annual vegetable gardens - about 40 square metres - are dressed with 70-80mm of topsoil, for a total of about 3 cubic metres. This purchase from a local landscape supplier with free trailer hire cost a couple hundred dollars and will pay for itself over years and years of increased vegetable yields. Using topsoil is similar to improving the thermal performance of the house with insulation - it slows the leaching of nutrients out of a garden just as insulation slows the passage of heat through the walls of a home. In the last two years, in our 70-80mm of topsoil, using organic methods we have grown a 4kg cauliflower, a 3kg broccoli, a 3kg purple cabbage, a 1.2kg red onion, and over 500 soft neck garlic.

But we have also had some failures - our first year of potatoes was pathetic, and I have had trouble germinating basil and courgettes this year.

On the other hand, we had ripe tomatoes before Christmas without a glass house.

Over the last decade-plus, I have been studying low-input sustainable agriculture (LISA), and experimenting with different methods, tools, techniques and strategies. I think I may have learned a thing or two worthy of sharing with others. If you would like to learn about boosting the productivity of your veg garden without significant investments of money or effort, you may be interested in one of the upcoming ECO School events as listed in the sidebar.

Nelson Lebo is co-founder of the ECO School with his wife, Dani. theecoschool@gmail.com - 022 635 0868 - 06 344 5013. They have renovated an old villa at Castlecliff with green principles and sustainability in mind.

- Wanganui Chronicle

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