The concept originated in Africa, and has been pioneered in Tokelau and Samoa by a legend of Pacific Island agriculture, Dr Malcolm Hazelman, who sadly passed away last month in Samoa.
A keyhole garden is designed so that the soil inside effectively holds moisture. The soil also receives beneficial nutrients due to an active compost pile placed in the centre of its keyhole-shaped bed. The notch shape cut into the round garden bed allows easy access to the centre of the compost well.
With Te Ipukarea Society already producing worm tea and compost from their worm farms and compost bin, staff have now taken the next step in creating a demonstration vegetable garden, by building a keyhole garden.
The first task is to identify a sunny site and then to mark and clear out a circular area roughly two metres in diameter. The outline of the garden is then to be marked with a low stone wall, or any other suitable material such as concrete blocks, coconut logs etc. One section of the wall is angled inwards towards the centre to act as a “keyway” to allow access for the gardener to get to the compost area
The rock or concrete block walls of the keyhole garden help to absorb heat, helping crops to thrive even during cooler temperatures.
Four corner posts are then placed securely in the centre of the keyhole garden to mark out the compost area. Chicken mesh is a possible material that can be wrapped around the posts to act as the walls of the compost heap.
Now, to fill up the keyhole garden. This step is quite important as it influences how well moisture is retained and how well-nourished the soil can be, making it more productive than a conventional garden. In order to achieve this optimal productivity, different layers of material are needed to be added to the garden.
The first layer can include iron scraps such as empty tin cans, broken clay pots and dry animal bones, to provide not only minerals to the soil but to assist with drainage during heavy rains. Soil is then placed on top to provide nutrients and scatters of wood ash to provide potassium. It must then be made sure that every layer slopes downwards from the compost well so water can flow properly into the soil around it.
When TIS staff cleared the section to make space for our keyhole garden, we were left with a large pile of hedge clippings and pawpaw trunks.
We used our woodchipper to shred all this leafy waste into chips which we will use as mulch around our vegetables, which will help retain moisture and suppress competition from weeds. We would like to thank the GEF Small Grants Project for funding our woodchipper, as a part of our waste management project.
While construction is under way be sure to start planting a variety of seedlings in a seeding tray so they can be ready for their new home once the keyhole garden is complete. Seedlings used for Te Ipukarea Society’s keyhole garden included cherry tomatoes, bok choy, cucumbers and capsicums.
Choosing the types of vegetables to plant is also important as it can influence soil nutrients and pest management within your garden.
For instance, it is advisable to consider “companion planting”, which involves planting different kinds of crops together which can benefit each other. Different methods include planting leafy crops next to root vegetables or planting pest resistant vegetables like onions or garlic next to regular crops. To best ensure that your garden will stay fertile and resist pests, plant a minimum of four vegetable types. Examples of root crops include carrots, onions, beetroot, radish, turnips and garlic. leafy crops include spinach, lettuce, mustard spinach and herbs.
Keyhole gardens are great for all households and schools. They don’t need much room, are easy to make and produce fresh locally made vegetables.
Instead of burning your leaf litter you can use it as mulch in your garden. If you don’t make your own compost, we recommend using locally produced Baker’s compost. This is available at Aquaflow Water Solutions in Tupapa and CITC Building Centre.
If you need more information on how to kick start your very own keyhole garden or think your school would be keen on building your own keyhole garden, get in touch with the Te Ipukarea Society team.