I am building Permaculture gardens in France and I am often asked to build raised beds.
But there is an issue I need your help with:
I like to build the footpaths on contour and use them as mini-swales. But because of the borders along the beds, the water collected by the footpaths don't infiltrate very well in the beds.
A French drain would get rid of the water, but wouldn't necessarily put it in the beds, which is what it sounds like the OP wants.
I would dig tiny trenches across the paths at regular intervals in the hard pack under the wood chips so that they run underneath the borders. The wood chips will hold pockets of space open for water to pass through the paths, into the drainage trenches (wood chip tiles?), and into the bottoms of the beds.
The woodchips will eventually decompose, so I would actually use terra cotta or unfired clay tubes, or pieces of broken clayware, to hold open the structure of the drainage trenches. If I had access to old-school terra cotta drainage tile, I would use those. Either way, I would probably augment the design for longevity with appropriately large-sized pebble fill to maintain the drainage trench structure, perhaps covered with a water permeable geotextile to keep the soil from filling the void spaces.
Or you could literally just design the borders so that every one in three or five boards are set slightly higher than the others, providing direct access to the soil in the bottom of the raised beds for water from where it pools on the hard packed soil under the wood chip path. This might be the easiest design to implement, but the drainage holes would need to be situated in dips of the hard pack.
There are options, some of them cheap and elegant in their simplicity, and others pricey but likewise elegant. Please keep us posted, or just point us to more of your beautiful garden shots, and good luck.
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My first question is... Are you sure the water isn't getting to the roots anyway? The plants are probably sending roots down fairly deeply in search of water. When they get to the edge of the bed it should get moister and encourage them to reach out under the retaining wall however far they need.
An option would be that when you build the paths and beds, dig down to the depth of the bottom of the wood/slate bed edges and compact the soil a bit. Maybe even put a crown on the path so the compacted soil encourages water to seep towards the edgers. Then build the 3" deep path back up with soil along the edges to hold the retaining wall boards/slate and wood chips in the middle.
thank you all for your answers !
and for your enthusiasm seeing this picture !
That's what we did in the pictured garden actually.
As you said Chris Kott the drains gets the water. As we build our french drains on contour, the water sits still in the drain and hydrates the gardening bed from below ground level. Your idea to dig tiny trenches across the paths seems good.
Indeed we would also rise the level of some of the boards.
Mike Haasl: thanks. I think that even with a compacted bottom below the path, the water is stopped from going to the bed by the bottom of the retaining wall.
Tereza Okava: could you send a picture of those old ceramic tiles ?
To integrate walking paths, I suppose they would have to pool water on one side against the "uphill" raised bed. The path would have humps at every contour level to retain water, and not drain. How long would standing water sit before it soaked through?
Beautiful garden. It has inspired change in mine :)
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