Fall Keyhole Garden Maintenance

Autumn is a great time to get your keyhole garden ready for next season

A very tired Keyhole Garden after a long growing season

As 2022 draws to a close, the keyhole garden looks pretty tired. It should be because, once again, it’s been a busy, and productive, season for this raised bed. All told, we ran 14 crops through the garden between January and October. It would have been more but the Roma tomato plant took over about 1/3rd of the bed for the better part of the year.

Now that it’s November, the tomatoes and basil are played out, as is most of the lettuce. We still have a few bell peppers and green onions limping their way to the finish line, but we’re going to call them “done” by the weekend and clear the bed for a little fall maintenance.

Fall Keyhole Garden Maintenance

Keyhole gardens generally don’t need any much maintenance, but after a long growing season, giving it the once over while it’s clear of plants offers the opportunity to fix anything that might have gone unnoticed when it was full.

1) Inspect the bed walls

The first thing to check is the general condition of the raised bed’s walls. If you used material like rocks, bricks, or concrete blocks to build the bed borders, there probably won’t be any issues beyond a loose stone or two. But if your bed is built from material like corrugated metal or, as in my garden’s case, wood, you may find broken or out of place slats, loose screws, rust, and similar conditions that need fixing.

My keyhole garden is built from cedar fence boards banded barrel style with stainless steel pipe strapping, so I check to make sure none of the boards are splitting and the screws holding the pipe strap to the wood are still firmly in place. I used to also try and stand up straight boards that were leaning outward, but after three years I’ve figured out it really has no effect on the raised bed’s structural integrity, and so I let them lean out a little if they want.

2) Prep the compost bin

As the weather cools off, now is a good time to check the compost bin’s condition and see what, if anything, is needed to keep it going through winter. Most won’t need anything. The insulation from the bed and the heat generated by the decomposition process is usually more than enough to keep things going in all but the coldest winter areas (USDA zones 5 and below). If you live in one of those zones, make sure to top off your bin with a deep layer of mulch like leaves and lawn clippings in the fall to keep your compost warm enough to survive the coldest parts of winter and give it something to eat once it starts to warm again.

In my keyhole garden’s case, the problem isn’t cold preparation, it’s too much unfinished compost.

Compost in need of a good stir

As you can see from the photos, I tend to let the keyhole garden off the leash as the summer goes on (read: I’m lazy and don’t do a lot of maintenance), so a lot of times it’s “vegetables gone wild” and the compost bin gets obstructed by plants growing over it. That doesn’t mean I don’t keep adding compostables – I find another angle from which to toss them – it just means I don’t turn the compost for months at a time.

With the bed cleared out, easy access to the compost bin is restored, so I can get in there and mix stuff up. Quite often the bin will be full of partially and completely composted materials all the way up to the bed’s soil level, so I shovel out the compost and sift it into a wheelbarrow. The fully composted materials get spread in the bed, and the partially composted stuff goes back into the bin nicely aerated and ready to kick the composting process back into gear.

3) Refill the soil

Once you’ve made any necessary repairs and set the compost bin up for the winter, the last thing to do is bring the soil level back up to the top of the bed walls.

Measure how much soil is needed to top off the bed

Over the growing season plants use the carbon, nitrogen, and other organic material in the soil to grow. The compost bin replaces some of these, but an active garden will draw down more than the bin can supply alone leading to lower soil levels as well as a higher concentration of inorganic materials like sand and dirt.

Using a yardstick or measuring tape, check to see how much the bed’s soil level has dropped over the season. With a little high school math you can figure out how much new soil I’ll need to top the bed off once again.

For those of you who don’t remember, you calculate the volume of a cylinder like this:

Volume=?r2h

(Or you can just let Google do it for you.)

Freshly sifted compost goes back into the keyhole garden

In the case of my keyhole garden, which is 8 feet (2.4 m) in diameter, the soil level has dropped by about 5-½ inches (14 cm), so I’ll need to add about 25 cubic feet (roughly two full wheelbarrow loads) of fresh soil to fill the bed back up to the top.

If you’re going to let the bed rest through the winter, this is also a great time to add a layer of a carbon-rich mulch like straw, leaves, pine needles, etc. That organic “blanket” will help the soil enrich itself over the winter. In the spring, turn it back into the soil a week or two before planting and you’ll have a nice, rich layer of topsoil your seedlings will love.

Growing all year long in the keyhole garden

If you live in a warmer climate (generally zone 7 and higher; zone 6 if your keyhole garden is in a sheltered area), you can actually keep the keyhole garden running all year long, which is what I do. With the exception of a couple of weeks each fall when I’m doing the above maintenance, my garden is in continuous production (1,300 days and counting now).

Figuring out the proper crop rotation for your garden might take a bit of experimenting, but I’ve found that I can grow cold hardy lettuces, brassicas like cabbage and cauliflower, and snow peas in late fall and early winter. When the days are getting longer in mid-winter (light is more important than heat), I rotate in carrots, onions, and herbs like dill, parsley and cilantro, which carry us through until the warm growing season lets us plant our spring and summer crops.

As an example, here’s what we grew in the keyhole garden in 2022 (keep in mind, a lot of these overlap with new plants coming in before the old ones are finished and pulled out):

(Technically, I haven’t planted the November stuff in the keyhole garden yet. They’re all seedlings started in the greenhouse and ready to transplant in another week or so.)

Winter seedlings in the greenhouse

It’s hard to overstate how productive a keyhole garden is, and how awesome it is to be able to walk out of your kitchen to pick something fresh for dinner.

Better yet, all this productivity comes with the additional bonus of being very efficient, sustainable, and really easy to maintain. Just a couple of steps once a year, and this garden will be a food (and occasionally, flower) machine year in and year out.

If you have a keyhole garden, you know what I’m talking about. And if you don’t, what are you waiting for? Large or small, these special raised beds are awesome.

Like that? Checkout these other keyhole garden posts