Keyhole gardens produce an amazing amount of food with very little effort, but to keep them productive, you need to renew the bed every now and then
The refreshed keyhole garden looks splendid in late December
Probably the coolest thing about a keyhole garden is that it’s super productive with almost no effort or input from the gardener. A little water, some yard debris and food scraps for the compost bin, and it’ll produce loads of fruits and vegetables all season long. Or, as in the case of some, all year long.
The magic of the keyhole garden comes from its design. It’s circular and raised so there’s no nooks or corners to mind. Every part is as easy to get to as any other without any excess bending or reaching. There’s a compost bin integrated into the center of the bed that provides a consistent supply of nutrients.
The keyhole garden’s soil layers are what make it so productive
And, finally, the garden is built with layers of soil, mulch and organic matter that offer an ideal combination of drainage, aeration, and temperature balance.
Time Takes a Toll
During the growing season the soil level in a keyhole garden (or any raised bed for that matter) will get lower as the plants convert it to food. Over a growing season, a soil level reduction of anywhere from 2 – 6 inches, depending on how hard the garden works, is normal.
If the soil drops just a bit, you can refill it from the finished compost in the garden’s compost bin. If it drops more than a couple inches, it’s still easy enough to top off with a few bags or a wheelbarrow load of fresh soil and/or compost.
Over a few growing seasons (my keyhole garden is now in its 4th year), however, the two lower layers of the garden will decompose and compact, lowering the bed level faster and further than plants alone over the normal growing season.
Over time, the soil can be drawn down quite a bit
While it’s tempting to just toss more soil on top to level up the bed again, all that additional soil will also increase the density of the layers below, squeezing out the airspace, and reducing drainage. Eventually this impacts microbial activity and leads to a bed that’s less productive and more work than it should be. As a result, to keep a keyhole garden at peak performance, every few years or so, it’s good to recharge the keyhole garden by relayering it.
Bottoms Up! How to Recharge a Keyhole Garden
In order to re-layer the bed, it has to be dug out, so it’s best to do this when the bed is empty (or mostly empty).
The keyhole garden (mostly) cleared and ready for a refresh
Personally, I prefer to do it at the end of the season since I’m cleaning the bed out anyway. Plus, because those new layers will settle over time, the extra weeks between the re-charge and new planting gives time to spot any sinking spots and level them off before plants go in.
Step 1: Dig out a wedge
The easiest way to go about relayering is to divide the keyhole garden into quarters like pie wedges. Then there’s no need to toss any dirt out of the bed, because it’s just heaped into the next wedge.
Dig out a wedge of the keyhole garden
Toss the soil to either side of the wedge
Dig out the top half of the wedge’s soil and toss the soil into one pile, then dig out the lower half and toss it into another. Keeping it separate makes it easier to mix the soil top-to-bottom when the wedge is refilled.
Step 2: Add a Coarse Wood Layer
Once the wedge is dug out, layer the bottom with coarse woody matter. It can be small tree branches (leaves on or off), woody shrub cuttings, even cardboard. Pile in the materials and compress it a bit to remove the biggest air spaces.
I used fresh-cut oak branches for my coarse wood layer
This layer provides good drainage and a long term source of organic matter. It’s also a bit of a barrier to burrowing pests like gophers, voles, ground squirrels, etc.
It should be about 1/4th of the height of the bed and dense enough that the next layer of materials won’t pour through the gaps, but loose enough that water and soil can still filter through.
Stomping the oak branches to compress them
Step 3: Add a layer of soft organic materials
On top of the coarse layer add a layer of easily decomposed organic materials like grass clippings, leaves, straw, old flower and corn stalks, etc. Compostables – egg shells, coffee filters, fruit and vegetable peels, etc. – can be tossed in here too.
I used partially composted straw for my soft layer
This layer provides aeration and ensures soil microorganisms have a plentiful source of materials to turn into the carbon and nitrogen plants need to grow.
Layer number two should be about half the total depth of the bed. This layer doesn’t have to be compacted like the first. The top layer will take care of that.
Add enough soft organics so it is twice the depth of the coarse materials
Step 4: Re-fill with the soil
The final step is to fill the wedge back in with the soil. The pile of soil that came from the top half goes in first, and the soil that came from the bottom goes on top.
There’s no need to level the wedge(s) until they’ve all been dug out and re-layered.
Re-fill the wedge with soil and move to the next section
Step 5: Level Off the Soil and Water Well
Once all four wedges have been re-layered and filled, rake the whole bed to make it even.
At this point, the soil level is usually higher than the side of the bed because of all the new material added below. Rake the soil so it slopes up toward the center where it meets the compost bin, and gradually outward to the edge of the bed.
The refilled and leveled garden bed
Watering the bed will help settle the soil and eliminate any air gaps that might be in the layers. The soil will continue to settle for several days, so when you see low spots appear, level them off by raking from the high point in the center of the bed outward.
Step 7: Good to Go!
The bed can be re-planted now, or allowed to rest until planting season arrives.
The refreshed keyhole garden planted with new vegetables in early December
Pro Tip – Feed Your Compost!
Whether you re-plant the keyhole garden immediately or have to wait until warmer weather arrives, make sure to add compost materials to the compost bin in the center. Even if it’s freezing cold, organic activity will continue and leech nutrients into the soil, giving the bed a bit of a kick start when you do finally get around to planting it. Once the plants get going, the bin will also have an easier time keeping up with their nutrient demands and you’ll get bigger, healthier crops faster.
Here’s my keyhole garden in late December, just four weeks after the bed was refreshed.
The refreshed keyhole garden looks splendid in late December
I built my keyhole back in 2019 for around $200, and as you can see above, it’s still going strong today. Moreover, it’s been in near-continuous production since that time, and we’ve harvested hundreds of pounds of fresh vegetables, fruits and herbs.
If you’re interested in building your own keyhole garden, I’ve included details on how I built mine below.