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Keyhole Garden

[DHT]Osiris

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Dec 15, 2015
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Looking for some thoughts on a keyhole garden. For any unfamiliar, it's a compact/efficient garden, about a 6' diameter circle with a compost hole in the center, and a small 'keyhole' to permit access to the hole itself. 'Bout 32"-36" high at the edge, 36"-40" at the center.
1615836894862.png


Realistically, I've got four materials I can build with. Treated wood as above, rock aggregate that's large enough to actually dry stack with, pavers, and cement blocks.

-Wood-
Pro: Straightforward construction, probably pretty stable due to using some kind of rod/stakes to secure the layers. Doesn't take up much room. No real concern about chemicals with newer stuff. Not bad on price.
Con: probably lasts the shortest amount of time (I'm seeing 7-10y cited as lifetime of pressure treated in contact with soil). Most expensive. Labor intensive to build (I only have a circular saw).
1615836910445.png

-Rock-
Pro: Looks pretty killer. Almost free (combo of gathering and cheap purchase). Last forever. Zero concerns of contaminants.
Con: Very labor intensive. I'll probably be terrible at stacking rocks and fail miserably. Frost heave will likely create a lot more work for me come next spring.
1615838183097.png

-Lipped pavers-
Pro: Looks pretty good, very clean and intentional. Lasts forever. Easy to assemble, not likely to be subject to heave.
Con: Most expensive. Very labor intensive. Moderate concerns of fly ash, alleviated by planting sunflowers amongst my crops.
1615838333852.png

-Cinder Blocks-
Pro: Easy to assemble (if heavy). Should last a long time, if I brace it correctly (rebar through the holes to prevent frost heave from shifting?). Not terribly expensive.
Con: Looks pretty ghetto. Same issue with fly ash. Still labor intensive.
1615838090253.png
Based on my calcs, I'd need somewhere around 220 12" pavers, or around 90 cinder blocks for the circle. I could make it a little smaller to save time/effort, but I'd rather not. Might be an alternative configuration that could get me more with less though. Here's some scribbles of my design concept.
1615838681880.png
~23' circumference to field a 6' diameter internally, costs for pavers on the left, cinderblocks on the right (I was primarily considering those two).

My inclination is to just bite the bullet, get the lipped pavers, do this whole thing once and call it good, in comfort that I won't have to do it again and won't spend much, if any time rebuilding in the future.

Thoughts, concerns with usage of any of these materials, or has anyone done this before that can give me tips?
 

lxskllr

No Lifer
Nov 30, 2004
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I don't like pavers. To me, it looks like a shortcut, and some kind of HomeDepot® brochure project. Wood's ridiculous unless you understand the impermanence and don't mind doing it over and over and over.... Cinder blocks... Does anything really have to be said about cinder blocks? That leaves stone. You know it's the right thing to do. You can do it, and it'll last if you take your time and pay attention to detail.
 

[DHT]Osiris

Diamond Member
Dec 15, 2015
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I don't like pavers. To me, it looks like a shortcut, and some kind of HomeDepot® brochure project. Wood's ridiculous unless you understand the impermanence and don't mind doing it over and over and over.... Cinder blocks... Does anything really have to be said about cinder blocks? That leaves stone. You know it's the right thing to do. You can do it, and it'll last if you take your time and pay attention to detail.
Isn't frost heaving a problem with dry stacking stone? It's literally surrounding a pillar of mushy dirt and we get into the negatives here.
 

bbhaag

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Jul 2, 2011
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Yeah I'm kinda with Lxskllr on this one. The paver and cinder block ones don't look the best to my eyes and if I was going to spend the time and money building something like this and then have to look at it for the next X amount of years aesthetics would be something at the top of the list to consider.

That being said while the stone one looks nice(the angle of the pic is a little weird)are you sure it would be "almost free"? I'm not sure were you are located but foraging for stone is no easy task even if you live in an area where this is possible. The time alone to go out to a spot and pick them up then load them in a wheelbarrow then haul them back to your truck then load them into the bed....uuggh I'm honestly getting tired just thinking about.
Even if you decide to buy them at your local garden center for convenience the price can add up. The stone I sell that looks similar to the pic you posted goes between $.25-.35/pound. Just something to consider.

I would honestly probably make the wood one even if the only tool you have is a circular saw. The angled cuts would be difficult but doable and the wood is easy enough to source at the local lumber yard/box store. Plus if you do need some additional tools to build it it's a great excuse to add to the tool collection am I right?:)

Have you considered lining the wood one with 6mil plastic sheeting? Staple it in place above soil line and that will help extend the life of the wood considerably. Like I said above just something to think about.
 

herm0016

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Feb 26, 2005
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the wood will last 5 to 10 years depending on your climate. we get 10+ out of wood, and that is good enough for me. we use pressure treated with synthetic roofing underlayment wrapped inside. dry stacking stone is an art form. the rocks last forever, but i bet you only get a few years out of the stack before they take advantage of gravity.
 

lxskllr

No Lifer
Nov 30, 2004
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Keeping in mind I'm not a stone mason, the approach I'd make is to lay the first course underground, and bring it up sloping towards the center like a buttress. They have stonewalls and stuff up north, and they last at least one lifetime, if not longer. bbhaag made a good point though. It takes *a lot* of stone to do anything. You'd be amazed at how quickly a huge pile of stone in the driveway goes, and how insignificant the structure you made with it is. I don't think it would be a 'finish this year' project unless you bought the stone, or spent most of your free time collecting it.
 

bbhaag

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Jul 2, 2011
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Keeping in mind I'm not a stone mason, the approach I'd make is to lay the first course underground, and bring it up sloping towards the center like a buttress. They have stonewalls and stuff up north, and they last at least one lifetime, if not longer. bbhaag made a good point though. It takes *a lot* of stone to do anything. You'd be amazed at how quickly a huge pile of stone in the driveway goes, and how insignificant the structure you made with it is. I don't think it would be a 'finish this year' project unless you bought the stone, or spent most of your free time collecting it.
Yep that is one of the things I noticed immediately from the pics. If you look at the stone one the depth isn't nearly the same as the others. The grade of the soil also slopes considerably compared to the others that are relatively flat which would have an impact on watering as well. Not to big of deal because most things planted in this type of setup have a max root depth of 20-30" but it is noticeable. Now you could change all that it just means more stone but that also means more money.
 

bbhaag

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One other thing I didn't even think about would be erosion through the gaps in the stone. Stones are so irregular that it would take extra time sorting through the pile to butt them up next to each other with as little gap as possible. I guess you could chisel them one at a time so each stone fits better but that sounds awful.

I guess you could line it with plastic like I mentioned above. I bet erosion is an issue with most of these styles so lining it might not be a bad idea with whatever style is chosen. Or I guess every couple of years you could top it off with fresh media which honestly has it's own set of merits but adds to the over all cost of ownership over the lifetime of the setup.
 

turtile

Senior member
Aug 19, 2014
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It seems like a lot of work with little in the way of advantages. Why do you want to use this design?

How do you continue to use the compost heap when it forms compost? It seems like a lot of work to dig it out and then have worry about the dirt around it from caving in.

Stone/block will require sharp gravel underneath and on the sides so it doesn't fall apart from water. Treated wood has a tendency to warp unless you use brackets. I'd go with composite decking with close bracing.
 
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turtile

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Aug 19, 2014
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I guess you could line it with plastic like I mentioned above. I bet erosion is an issue with most of these styles so lining it might not be a bad idea with whatever style is chosen. Or I guess every couple of years you top it off with fresh soil which honestly has it's own set of merits.
Plastic will capture water and cause the wall to fail with time. It also prevents air exchange needed for plant roots and beneficial soil organisms.
 
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[DHT]Osiris

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Dec 15, 2015
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Great thoughts here.
That being said while the stone one looks nice(the angle of the pic is a little weird)are you sure it would be "almost free"? I'm not sure were you are located but foraging for stone is no easy task even if you live in an area where this is possible. The time alone to go out to a spot and pick them up then load them in a wheelbarrow then haul them back to your truck then load them into the bed....uuggh I'm honestly getting tired just thinking about.
Even if you decide to buy them at your local garden center for convenience the price can add up. The stone I sell that looks similar to the pic you posted goes between $.25-.35/pound. Just something to consider.

I would honestly probably make the wood one even if the only tool you have is a circular saw. The angled cuts would be difficult but doable and the wood is easy enough to source at the local lumber yard/box store. Plus if you do need some additional tools to build it it's a great excuse to add to the tool collection am I right?:)

Have you considered lining the wood one with 6mil plastic sheeting? Staple it in place above soil line and that will help extend the life of the wood considerably. Like I said above just something to think about.
Upstate NY, farmland, former glacier runs so lots of glacier rock. Almost every yard has a 'rock pile' from what's been pulled out of their yards, and we have a river behind our house that's basically a quarry. That said, a lot of it is river stone which is basically impossible to stack in a clean way without mortar. You're right, it is a huge amount of work though, and a few hundred bucks isn't that expensive compared to back pain.

Regarding plastic sheeting, that was a thought too, as long as it didn't interfere with oxygen movement to the roots (as @turtile said), or drainage. I don't want a swamp either.

It seems like a lot of work with little in the way of advantages. Why do you want to use this design?

How do you continue to use the compost heap when it forms compost? It seems like a lot of work to dig it out and then have worry about the dirt around it from caving in.

Stone/block will require sharp gravel underneath and on the sides so it doesn't fall apart from water. Treated wood has a tendency to warp unless you use brackets. I'd go with composite decking with close bracing.
Thanks for the question! Essentially, I'm not retired and have enough stuff to do on my property without spending a huge amount of time gardening a tiny square of dirt. This is a space efficient design, drought resistant, and can feed a family of four, so that's good enough for me. There's also very little to maintain once set up, so I don't have to spend all summer weeding it which is what I did with my pathetic COVID garden last summer. Regarding the compost, you have rocks underneath to provide drainage, but the 'compost tea' leaches into the dirt and underneath to provide nutrients to the plants, so basically you just keep the composter topped up and keep watering it. We have a separate composter for 'everything else'.

This is probably the ugliest garden design I have ever seen. o_O
1615890449868.png
Function over form, brother.
Something similar but looks much better.

View attachment 41152
That's essentially identical, just square instead of round. You lose efficiency in the corners, and maximize planting area if you round it all off. That said, you can just make an octagon or so with wood and gain 90% of the efficiency of round with little effort. Still run into the same issues with bowing and rotting wood though.

Also, for that specific design, those boards would probably warp/crack in the first winter. I was worried enough with the 3.5" landscaping timbers, much less some little 1" panel boards. It might work if those midpoint braces are 1'+in the ground but it doesn't give me high hopes.
 

mxnerd

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Jul 6, 2007
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How can a circle be more efficient? Let's say the radius is diameter is 6 ft, and you have a walk-in area that's 2ft wide on the outside

the circle length is 6 x 3.14 = 18.84. now you only have 28.274 - (2/18.84)*28.84 approximately 25 sqft left

with a 6ft x 6ft square and a walk-in cutout 2x3, you still have 30 sqft left. For Homedepot planter blocks, you use 2x6 board.

Untitled3.png

==

Well, someone did this.

Untitled4.png
 
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[DHT]Osiris

Diamond Member
Dec 15, 2015
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How can a circle be more efficient? Let's say the radius is diameter is 6 ft, and you have a walk-in area that's 2ft wide on the outside

the circle length is 6 x 3.14 = 18.84. now you only have 28.274 - (2/18.84)*28.84 approximately 25 sqft left

with a 6ft x 6ft square and a walk-in cutout 2x3, you still have 30 sqft left. For Homedepot planter blocks, you use 2x6 board.

View attachment 41156

==

Well, someone did this.

View attachment 41163
The whole point is to have an even distribution of compost tea from the center to the edges. If it can reach the corners, you could have made it bigger. If it cannot reach the corners, you aren't supplying the garden with enough nutrients. You *can* make it a square, you're just shorting yourself results. It might be worth looking at the above though, as it's so easy to put together I might not care about rebuilding it periodically.
 

bbhaag

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Jul 2, 2011
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Great thoughts here. Upstate NY, farmland, former glacier runs so lots of glacier rock. Almost every yard has a 'rock pile' from what's been pulled out of their yards, and we have a river behind our house that's basically a quarry. That said, a lot of it is river stone which is basically impossible to stack in a clean way without mortar. You're right, it is a huge amount of work though, and a few hundred bucks isn't that expensive compared to back pain.

Regarding plastic sheeting, that was a thought too, as long as it didn't interfere with oxygen movement to the roots (as @turtile said), or drainage. I don't want a swamp either.
Sounds like you have a steady supply of rocks which is cool and is seems like you have an idea of the amount of work required to gather them from around the area and bring them back to build the garden. I won't get into the other aspects of the over all efficiency of the garden or the practicality of this design. That's up to you to decide.

I will say one thing though plastic sheeting in NO way will interfere with the growth of your plants. It won't prevent oxygen from getting to the roots in any way and will not hinder their production in any way. If you decide to use plastic sheeting to line the walls it will have no affect on the plants you put inside the garden. Period.
 
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[DHT]Osiris

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I will say one thing though plastic sheeting in NO way will interfere with the growth of your plants. It won't prevent oxygen from getting to the roots in any way and will not hinder their production in any way. If you decide to use plastic sheeting to line the walls it will have no affect on the plants you put inside the garden. Period.
That's good to know! Alleviates one of my primary concerns about non-natural elements, as I can simply plastic wrap the whole internal and call it gravy.
 

Scarpozzi

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All of my raised beds in my garden are made of a combination of treated 2x4s that I ripped in half to make thick stakes for the corners and centers...then the sides are all made of dog ear fencing. I think the 6' long treated fencing boards are like $1.65. That was about the cheapest treated lumber you can find....cheap enough that if you get stuck having to replace it in 5....whatever. The 2x4s tend to rot pretty quick in the ground. The sides tend to bow out and dry enough that they'll get brittle and crack....but if you don't mess with them much, you can get 5 years out of them. If you do mess with them, it's cheap to replace pieces and parts as they go.
 

mxnerd

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I would say if you put bricks underneath lowest piece of boards so the board will not contact the ground directly, the board will last a lot longer.

And if you use outdoor construction adhesive to glue the boards together, it will be even stronger to prevent warping.
 
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[DHT]Osiris

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Went with pavers, more expensive but i'd prefer a clean look and for it to last. I'll post pics when it's built!
 
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bbhaag

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Can't wait to see the pics! Have you thought about what growing media you are going to fill it with once it's built? If you're looking for suggestions I'd recommend a soilless mixture containing peat moss, compost, and perlite. If it's in the budget you could also add some vermiculite but the cost has gone through the roof over the past couple of years.
 

[DHT]Osiris

Diamond Member
Dec 15, 2015
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Can't wait to see the pics! Have you thought about what growing media you are going to fill it with once it's built? If you're looking for suggestions I'd recommend a soilless mixture containing peat moss, compost, and perlite. If it's in the budget you could also add some vermiculite but the cost has gone through the roof over the past couple of years.
Everything below the 8" line is just whatever crap I can dig out of the pile next to our property. I was just going to be lame and fill the top 8" with 50% 'vegetable' potting soil and 50% aforementioned crap. I'm banking on sunflowers pulling out what I don't want to be there, and compost tea adding what I do.
 

[DHT]Osiris

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7' hole is in, delivery from Home Depot got delayed so I've got a few days before I start doing more. Slight grade, so 4" on one side, 3" on the other. Probably just going to backfill the 3" side with some more dirt to even it up to the same depth all around. Mostly flat, mostly tamped (tamper's delayed too).
1616270012058.png
 

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