Monday, September 2, 2013

African Keyhole Garden - Step 1

This old dog is learning new tricks. I've been introduced to the idea of an African keyhole garden.

When it was first suggested that I check these gardens out, I thought they were nothing special, just a raised bed with an aisleway cut into them for easy access to the out of reach plants. Wrong. Sure, a standard keyhole is like that, but these African developed ones are different. These are designed for low water useage and no commercial fertilizer., my interest was piqued.

First in place, the central core. Sue J posing with the post pounder. 

African keyhole gardens are built around a vertical compost core. This compost is held in place via a basket of some sort. I suspect one could devise one of these gardens without a physical basket, but that will be a future experiment. For now, the basket will be used because it is easy and visible. 

For this first garden attempt (being constructed at the community garden), we will be builting it with available materials that cost almost nothing. 

Step 1--- We took a piece of donated hardware cloth and roll it into a tube four feet high (3 1/2 to 4 feet height is what we aimed for) and between 1 and 1 1/2 foot in diameter. Next, we pounded four rusty old t-posts (salvaged from discharged fencing) into the ground close enough so that the hardware cloth tube would slide down over them. The idea --  to keep the tube from collapsing when the garden is filled with dirt.

Pallet pieces in place. You can see the keyhole on the left. 

Step 2 - We took 6 wood pallets (a local food market donates these) and cut them to 26 inches. Why 26? Because it's an easy spot on the pallet to make the cut and it is close to 24 inches, the height we were targeting for the sides. We decided to have the slats run horizontally for stability. Two more pallets were cut on an angle going from 26" to 36". These will be for the keyhole. 

Step 3 - Assembly. We set up the two keyhole pallets then added the side walls so that it sort of looked like a hexagon. Using wire, we wired the pallets together and to the hardware cloth core. We could have nailed it all together but we opted to use the wire so that the garden could be easily dismantled.

Plastic sheeting to line the garden to prevent drying out due to tradewinds. 

Step 4 - Using a sheet of discarded black plastic, we lined the interior sides of the pallets. On the keyhole section we also covered the exterior walls just because it will help protect the garden volunteers from getting splinters as they use the keyhole. We had extra plastic available, so we used it. The reason for the plastic is twofold. It will help keep the soil and organic material inside the garden, plus more importantly it will help retain moisture. Some regions get too much rain but not us. So drainage and waterlogging is not an issue for us. But having the soil dry out due to tradewinds is a concern. We used plastic because we had it, but we could also have used a tarp, plywood, metal sheeting, etc.

Cardboard lining the sides, protecting the plastic sheeting during the fill stage. 

Step 5 - With the plastic all neatly in place, we now lined the walls with cardboard. Reason : to keep the plastic from being damaged during the filling process. We then lined the bottom with a thick layer of cardboard. The tropical grass here is very aggressive, so an inch or two of cardboard will help prevent it from growing up through the bed. The cardboard will also help keep moisture inside the bed. 

Central core bin that will receive various manures and compostable materials. These nutrients will
eventually feed the keyhole bed as water is added to the core. 

Step 6 - Load the bottom half of the bed with coarse organic material. This material will slowly decompose. We used old wood branches, coconut fronds, coconut husks, coarse grasses, banana fronds, sorghum canes. We gave it a dusting of garden soil and ash. This material as it decomposes will need nitrogen. Excess nitrogen will naturally leech out of the upper part of the bed and thus be captured by this coarse material.

Layer of coarse material that will slowly breakdown via fungal and bacterial decomposition.
Coarse grasses, old sorghum, coconut husks, coconut fronds, and wood. 

Step 7 - Water the material well and cover it with wet newspaper. 

Next a layer of wet newspaper on top. Now its time for the serious filling up of the bed. 

Step 8 - Fill the bed lasagna style. Layers of garden soil, grass clippings, chicken litter, compost, horse manure, wet newspaper. You can use just about anything. Soil amendments can be dusted on various layers -- wood ash, biochar, bonemeal, coral dust, lava sand, a little ocean water, etc, the idea is to create layers so that moisture can wick out from the central core. This is essentially a layered compost pile.

The first layer of the finishing phase. Lasagna laying of grass, compost, wood ash, bone meal,
and garden soil, wet newspaper,  plus a little chicken pen litter. The top 3 inches will be garden soil. 

We didn't get this garden finished yet. That's for next week. 


  1. Love it! I had never heard of the African keyhole garden beds...ingenious!

  2. I now have the keyhole garden full,so I'll take some photos and post an update.

  3. i love what you have done .I have a lot of ?s,they will not fit in this box.Can u please give me your e-mail address so i can e-mail u the ?.My e-mail is u.Donna

    1. Welcome Donna! Anyone can email me at