What Are Keyhole Gardens?: How To Build & Maintain These Sustainable Raised Gardens

KeyHole Gardens Are Literally Lifesaving. Developed To Cope With Severe Weather Conditions & Adversity They Are New & Also Suitable For UK Gardens. In this Article I Explain The Why, Where, When, & How Of Keyhole Gardening.

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I used to think keyhole gardens were a useless passing fad. I was wrong.

They are something we should all consider simply because they can teach us so much about gardening. Developed by the Consortium for Southern Africa Food Security Emergency (C-SAFE), in Lesotho in the mid 1990s, they pull together many basic but very important aspects of gardening and horticulture.

Why Were Keyhole Gardens Developed?

Lesotho is an arid area with a lot of desert and not enough rainfall. And in the 1990s it had some of the worse HIV/Aids rates in the world. So C-SAFE wanted to develop a gardening technique that overcame the environmental conditions and made gardening easier for those with medical issues.

Keyhole gardens, being raised, meant those suffering from various AIDS related medical conditions didn’t need to bend and that the keyhole design allowed plants to make best use of stored water and nutrients within the garden.

What Do KeyHole Gardens Look Like?

Well, they aren’t as small as a keyhole? The name refers to the shape which is circular, like a cake or keyhole, with a wedge cut out for access. They are normally waist height, (though I’m seeing many much lower in recent times) with a stone/brick wall exterior. The wedge leads to central “compost bin” in which green waste is added. As it breaks down it feeds the nearby soil.

The “soil” in the garden is usually started in a similar way to Hügelkultur gardens, with water retaining material such as wood or even cardboard. Compostable material is added plus a layer of soil to top it. In most designs the soil slopes towards the outer edge of the structure to give slightly “tiered” effect.

Similarities To Established Gardening Techniques

Keyhole gardens take the best features of many other gardening techniques and blend them together into a new and unusual design that works across many parts of Africa and beyond.

The construction is a bit like a Hügelkultur heap in terms of the material used in the body of the garden. And as it decomposes and potentially provides heat, it’s also not unlike a hotbox, or the Victorian compost heaps on which they grew marrows, melons and other warmth loving plants. I’ve yet to see a covered example, but I can envisage the potential to add a cover to the garden that would trap some warmth rather like Les Mariachiers Parisiene did on their glass covered beds. I see it as a sort of teepee type structure.

No Dig also contributes to the technique as these beds are often covered in a mulch or compost and aren’t dug.

And the use of a compost bin in the centre of the bed is similar to the way a SubPod can be used.

There is a high degree of alignment with permaculture concepts within true keyhole gardens.

Finally, it’s a bit like the raised beds I see so many TV garden presenters ranting on about. I can see the sense of it here, as this is a specific application, though I’m still not convinced in many other situations.

Keyhole Garden Benefits

By combining the positives aspects of so many other gardening techniques, I can sum up the advantages of keyhole gardening as follows: –

Nutrient Rich Soil Production In Keyhole Gardens

These gardens are essentially very large compost heaps and slowly decompose whilst feeding the plants. More organic material can be added to the central “bin” over their growing season. And, when the organic material shrinks the body of the garden can be topped up with more waste.

In some cases I’m seeing a lot of soil added to these gardens. This makes sense when it’s for the top layer, but adding too much low down in the body of the heap is going to lessen the amount of organic material and hence decomposition and moisture retention.

Keyhole Gardening Retains Moisture & Need Less Watering

By using volumes of absorbent organic material such as carbon rich cardboard, organic material including wood and straw, the heap can hold moisture behind its rock, stone or brick walls for a long time. Grey water can be added to the central bin and will percolate there garden at a depth. This encourages deep rooting in the plants.

Where there walls are wide, the top can be sloped into the garden so that any rain or dew will run into the garden.

I’m seeing an increasing number of videos showing very low level keyhole gardens. These are easier and quicker to build but, as they lack large volumes of organic material, cannot retain as much moisture. Nor can they decompose into a good volume of organic rich compost such as you’d get from a compost heap.

Keyhole Gardens Are Very Accessible

The original beds were built at waist height to aid those with AIDS having to bend. This height means that plants can be easily reached for planting, cultivation, and harvest. They can also viewed and pests and diseases observed. This means that insects and caterpillars can be removed without effort, so giving better cared for plants!

Keyhole Gardens Utilises Green & Household Waste

All sorts of green waste can be added to the gardens at the time of building them and during their use. This both focuses the mind on the circular garden economy and aids soil production.

How To Build A Keyhole Garden

Methods vary a bit depending on materials to hand.

Mark out a circle, approx 2 metres in diameter or slightly bigger.

Build a wall of stone, blocks, rocks or bricks to waist height. Where stone of brick is not available branches are sometimes woven to form a circular retaining wall.

Include a keyhole shape to enable access to the centre of the structure.

Add a bin to the centre of ht structure .. it might be of weld mesh, wire or woven willow, whatever is to hand and suitable.

Now line the based with absorbent material such as cardboard. Soaking it in water before adding ir helps ensure it starts wet.

Add logs, branches, twigs and green waste as you would in a hugelkutur heap. Include more cardboard in the mix.

When nearly at the top add a layer of soil or wet rotted compost in which to plant.

The top layer can be sloped from the centre to the outside.

Add a mulch or compost layer.

Add your plants.

Stand back and enjoy!

What Can Be Grown In a Keyhole Garden?

Most things can be grown, but let’s be practical. Trying to grow tall crops such as runner beans, or cordon tomatoes, on top of a high garden just isn’t practical. But shower crops such root veg, leafy crops, short growing bushy plants and crawling plants will do well.

I’ve seen lists that include crops such as as onions, garlic, shallots, carrots, and beet and leafy crops such as lettuce, kale, spinach and herbs. Others have listed veg such as peas, beans, marrow, courgettes, and melons. Personally, if water is an issue, I’d go for the plants that don’t have high water requirements.

Keyhole Garden Improvements

Keyhole gardens are circular. This takes up a lot more space than square or rectangular beds.

I’d like to see some research done on making the beds square. This way the corners might be slightly dryer but this might be to the advantage of some crops. Square beds give many advantages. Firstly in terms of size. A round bed with a two metre diameter is 3.14 square metres. A square bed with two metres from side to side is four square metres. That’s nearly a third bigger.

Secondly, I see sense in water rain and waste water harvesting in conjunction with keyhole beds. Hoses running from the down pipes on buildings could be run direct into the centre of the beds where they could act as “Swales” to hold back and retain water when there is plenty. Clearly, a proportion might first want to be diverted to into tanks, fish ponds or for human consumption.

Grey water might also be piped to them in some cases.

Do Keyhole Gardens Smell?

Not normally. No more than any other type of raised bed.

However, if you add smelly material to the central bin, or very smelly grey water, there might be. smell issue. However, this is more a matter of poor management than a feature of a well kept garden. They should be smell free.

Do Keyhole Gardens Attract Vermin?

Ditto my answer to the question of smells. They shouldn’t.

But if you were to add meat, fish oil other material that is attractive to rats and other vermin don’t one surprised if they appear. Again it’s a matter of good or poor management.

Where Were Keyhole Gardens Developed?
As mentioned previously the keyhole concept was developed in Lesotho. But the original,work was from Zimbabwe. It then spread to a number of other African countries, including, Rwanda, Ethiopia, Kenya, Nigeria and Sudan.

C-SAFE oversaw the building of around 20,000 of their gardens, of whichb90% were still operating when reviewed a few years later.

Keyhole gardens are now to be found in many countries. However many fail to follow the original concept with a central composting bin. And many are just keyhole shaped raised beds. In both cases I don’t regard them as true keyhole gardens as they lack these essential features.

The following video shows a keyhole garden being built. If you want to build one I’d suggest fewer people might get it done faster!