Bumbleseeds Recommends Keyhole Gardens!

Keyhole Gardens for Simple Composting Solution

Composting for us has never been easier! Using our version of a simple yet highly effective gardening concept, keyhole gardens allows us to dispose of our kitchen waste quickly and easily, and enables us ease of access to the built-in composting center in our raised bed garden. The compost center not only makes composting a breeze but it also provides nutrients directly to the soil and our garden contents.

The keyhole garden concept originated in Africa and was developed for people who were ill and could not look after a traditional garden; it typically refers to a round shaped garden and the term ‘keyhole’ is used because it has a keyhole shape (circle and wedge) on one side of it when viewed from above. Imagine a pizza with a ‘dough ball’ in the centre and one slice is removed; that ‘dough ball’ is the composting center and the slice removed allows easy access to put compost into that center.

How it works

The round keyhole design is taller in the middle and gradually slopes down to the edges. The contents or layers added to the compositing center or ‘basket’ will distribute nutrients from this center. Our keyhole garden was built on a slope so we left the top surface entirely level. Most keyhole gardens are positioned close to the kitchen for ease of access to add kitchen waste and for harvesting.

Keyhole gardens are ideal for intensive planting, plants are placed very close together to maximize production and help to repel weeds and retain moisture.

We decided to experiment with the keyhole garden concept...we only had a small area of yard that we could install a vegetable garden bed. This area had two key drawbacks; it was on a slope and we had so many large tree roots that a logical option was a ‘no dig’ raised garden but it was full day sun and a great spot if we could find a good planting solution.

A rectangle shape for that area would allow us easy access to maintain the garden, and for walking through our yard. We decided to combine a no-dig, raised-bed, keyhole garden concept; placing the compost center at the topmost shallow end that would work with the slope; we wanted to see if the nutrients from the composting center would work its way down to the other end of the garden. As a first time experiment, it works very well!  

Our keyhole rectangular garden was laid out with the 4 x 4 pieces of wood and screwed together ensuring it was square. We covered the entire bottom inside this rectangle with cardboard which was then soaked with water. We also continued the cardboard up the interior walls, about six inches, to help hold the soil mixture until it got settled in. Layers of twigs were added next covering the bottom of the bed and this was topped off with a mixture of 90% soil and 10% sand to make it well draining. Using cardboard is a great way to suppress weeds and helps retain moisture!

We decided to experiment again - instead of using the ‘basket’ for composting like the example from Africa below, we fashioned a ‘circle’ out of galvanized deer proofing wire and placed it at the top end of the shallowest part of the garden bed. This circle sat on the bottom which was covered with cardboard that was ‘watered in’.

We lined the wire circle with cardboard – this was later removed when the soil and sand mixture was added overall and our first layers of browns and greens were added. This wire composting center works very well so far. We water the layers down when they are added; so far it appears to be adding substantial naturally based nutrients to the garden vegetables in the entire garden bed as everything is growing and healthy.

What Can You Put in Your Compost Center?

Having a built in composting center that utilizes a number of layers of materials to retain moisture and nourish the soil makes this more productive than a conventional garden. Composting ‘greens’ and ‘browns’ and layering each in the composting center will ensure your keyhole garden nourishes your soil and its contents:

Greens: (Nitrogen) green compost ingredients are anything soft with a higher moisture content such as grass clippings, kitchen scraps, and garden trimmings; these have a higher nitrogen content, rot quickly and encourage fast microbial growth. Greens can become very wet and compressed and will smell – you will need to balance out the density and add enough brown matter to introduce more aeration to the mix to keep it balanced. Note: evergreen clippings can take a long time to compost and will slow down the composting process – avoid these.                                                                 

Browns: (Carbon) refers to any organic matter which is rich in carbon.              Any plant waste which is dry, fibrous, and hard is generally recognized as brown and includes paper, brown paper bags, shredded woody material, sticks branches and straw. Browns are more resistant to decay. Consider these as the slow-burning food for your compost heap. Large logs, thorny branches and larger woody items will be too large to break down; you will need to chip or grind these prior to adding them. The addition of greens helps to promote moisture retention and decay; keep a layer of brown on the top of the compost to discourage animals

These layers of green and brown materials keep the composting process working successfully. After the first layer of brown (cardboard and twigs) materials, we added a layer of green - our uncooked vegetable scraps were placed into the keyhole garden center. We then added a layer of dry manure (which we keep close by), and eggshells and more soil. These layers replenish the soil nutrients as the plants grow.  

What About Watering?

Even though keyhole gardens might need less water than conventional gardens, gardeners need to water regularly to keep the topsoil moist. Clean water can be used directly on the topsoil just like a regular garden, but “grey water” from washing hands, laundry, and dishes can be poured into the central basket. The layers and the composting in the composting center will clean the water sufficiently for the plants to use it.

As the layers of your keyhole garden decompose, dry manure and topsoil should be replenished after each season so that it does not become short on nutrients. Also, if the topsoil turns grey or sinks below the garden walls, this is your cue that it is time to add topsoil and dry manure.  If vegetables stop growing well and there are no pests or diseases present, you may not have to remove all of the soil but simply top up the soil with more soil and manure. If you do find pests or disease you will need to remove the old layers of soil and start again. After four seasons or years it would be good to completely replenish the entire bed and start fresh.

Benefits of A Keyhole Garden:

  1. Nutrients: short term and long term benefits are realized because the central composting center contents of organic layers helps to continuously feed the garden and enrich the soil.
  2. Retains moisture: the layers of organic material soak up and retain moisture which is beneficial as the garden requires water less frequently and in smaller quantities.
  3. Easy to maintain: the soil re-nourishment and moisture retention properties of the garden help to reduce the amount of time and effort required to maintain the garden. The raised garden design is also easily accessible. The round design is especially easy to access the central composting area.
  4. Low cost solution: keyhole gardens are typically low cost as you can use almost anything to make one. If stones are used they hold heat in throughout the cooler evenings, pallets can be used in whole or taken apart for the frame; any building materials like steel sheeting, pressure treated wood etc can be resourced and reused.

For our Bumbleseeds keyhole garden, we reused old and new 4 x 4 lumber and finished the outer edges off with wood offcuts from another project. Cardboard was used for the bottom and a piece of deer fence was used for the composting center.

Note: The composting center, (if made with trigs only in the example below) will decompose over time and likely within 1 or 2 years, and should be replaced. The garden wall near the composting basket should be made so it can be pulled away which allows gardeners to remove the rotted basket and replace it with a new one.

Keyhole Gardens Contents:

What is recommended to grow in a Keyhole Garden:

  1. Leafy greens such as kale, lettuce and spinach; we found our chard is doing very well and bigger than our container grown chards.
  2. Herbs: cilantro is doing very well in the shallow end; most herbs will do well provided you take the root into consideration and plant accordingly.
  3. Root Crops: beets, carrots, garlic and onions do very well in keyhole gardens.

We planted carrots and cosmos in the deepest part of the garden bed, lettuce, shallots and chard in the middle, and cilantro and zinnia in the shallow end.

What is not recommended:

Any vegetables with wide reaching root systems such as tomatoes and zucchini may not do very well in a keyhole garden unless the depth will allow for the root growth and reaching to heights as they grow taller.

Here’s what we read before starting our improvised keyhole garden according to our needs: https://en.wikipedia.org/wiki/Keyhole_garden


Looking to Make an Authentic Keyhole Garden?

  1. Clear a circle approximately 2 metres across and remove all grass and plants; pound 4 corner posts for the composting basket into the ground; as big as required.
  2. Mark the outline of the garden with stones. Leave an access point toward the center in one place so that gardeners can reach the composting basket easily. (If stones are unavailable, the garden walls can be made of any sturdy, permanent material, such as old tires.)The composting basket is finished by encompassing the 4 corner posts with either sticks or rope to keep the contents inside of this area; the composting basket is lined with thatching grass so that compost materials and water will flow from the basket into the garden soil (once soil is added).
  3. Construct each layer so that it slopes down from the center basket to the edges of the garden so that water will flow from the basket into the soil of the garden

Layer 1: the first layer in the garden is composed of small iron scraps and iron cans (from food or beverages), aloe leaves, dry animal bones (not fresh animal bones), or broken clay pots. The iron, aloe and bones provide minerals to the soil as they decompose, and the broken clay aids in drainage of the garden so that it will not become flooded after storms. Fist-sized stones can be substituted for the broken pots. If bones are not available, they can be left out.

Layer 2: a layer of wood ash is added to provide potassium and thatching grass to provide moisture retention.

Layer 3: a layer of soil is added on top of the wood ash; the addition of soil helps to decompose the iron, bones, aloe, and ash, freeing the nutrients those materials contain so as the plants are able to use these.

Layer 4: a thick layer of soil and dry manure mix is added on top. (If wet manure is used, it can kill the young seedlings that are planted later.) As the garden grows taller, stones are added around the edges. The stones should always rise a bit higher than the soil.

Whatever the shape, size or location you decide on…the concept is brilliant. If you are looking to experiment with a keyhole garden, we highly recommend making it even easier by using a raised bed design of whatever size you can fit, and making the composter center as large as your family requirements need to compost all of your kitchen waste. Keyhole Gardens are extremely easy to maintain and we like the added benefit of using organic layers to feed our growing food source.

Bumbleseeds highly recommends keyhole gardens! Our crops are healthy and full of flavour; we can pick a salad and eat it fresh within minutes. Our chard can be picked at 5:00 and sautéed and eaten by 5:20. So enjoyable!