Friday, September 14, 2012

Pavers amidst groundcover: putting in a secondary pathway using sheet composting

Out in the garden there's a little path, perhaps 30 or 35 inches wide, which runs between two semi-raised flower beds. Until a few days ago, this little alley-like path, about 20 or 30 feet long, was "paved" with grass.  However, being so narrow, it had become increasingly a pain to mow and trim.  The path isn't much used for walking because a much broader path parallels it, but it remains important because it is the only access to one of the beds it borders.

My goal is to reduce the mowing and trimming while maintaining the path as a secondary walkway, yet not add so much paving that the area will get hot during the day, or will feel barren. Further, I have to be able to do the whole project by myself, meaning that the inputs have to be fairly light.

It seemed to me that a paver pathway laid amidst a ground cover would suit the situation--the pavers would maintain the path, while the ground cover would soften the pavers and keep the area from becoming hot.  Further, separating the pavers with a ground cover would mean fewer pavers required to fill the area--less lifting for me!  Round pavers give more bang for the buck--providing a spot to land your foot, but weighing less and taking up less room than a square paver of (seemingly) "the same size." Plus, we've used round pavers in lots of other pathways, so they're a signature material for this garden.

After cogitating a bit, I installed a paver-and-groundcover secondary pathway as follows:

1. As stated above, the path run between two semi-raised flower beds.  Each bed is bordered with two layers of limestone landscape blocks--2-3" high, 6" wide and variable lengths.

2.  Between these borders, I laid newspapers in the pathway.  The newspapers were first wetted, then applied 8-10 sheets thick, in an overlapping pattern. If the blocks had not been there (in other words, if I were laying border blocks just to outline the path) I would have laid the newspapers first, them put the block atop the newspapers.  However, since the block was already laid, I just got as close as I could with the wet newspaper sections.

3. Next came a layer of corregated cardboard which had been kicking around out by the recycling ever since we got a patio table delivered--a huge sheet of corregated which had come through several rainstorms intact.

4. Over the cardboard, I laid pavers--for this project, I chose round concrete pavers stones 20" in diameter.  For variety, I added a few 12" steppers, as well as one 24" honker for right in the middle of the path. All these pavers were loaded into my car at the stone yard, and I drove home with the heavy load at low speeds, with the blinkers on.

5. On top of the cardboard, and around the edges of the pavers, I applied a thin scattered layer of pine bark nuggets.  The cardboard was about 1/3 to 1/2 covered with this thin layer.


6. Next came a layer of sterile potting mix. For this project, I used pro-mix (an organic growing medium which also contains some perlite, a wetter and which is pH adjusted). However, although pro-mix is handy stuff, the fact is that I bought it because it was on sale.  I would have used any sterile potting mix which happened to be on sale at the big-box store.  The combined layer of pro-mix and nuggets came just below the level of the round pavers.

7. Into the pro-mix/nugget planting medium, I placed 2-4 inch long sprigs of Angelina sedum.  There are many stands of this all around my garden--it is one of my favorite ground covers--and I harvested a strand here and a strand there until I had a big armful.  The shorter sprigs were pushed about half-way into the pro-mix/nugget medium, longer sprigs were laid on their side and covered half-way along their length with medium. Experience shows that in the climate conditions of my garden, Angelina can be expected to root readily under these circumstances. (In fact, it will root into bare soil, so I expect it to really take off in this soft springy planting medium.)

Angelina sedum in an established planting, fall color


8. To bring the final level up to the top of the pavers, I topped all with cocoa hull mulch, placing it carefully by handfuls around the sprigs.

The basis for all this rigamarole is a rather old-fashioned method known as sheet-composting. (Sheet composting is currently staging a comeback under the catchy name "lasagna gardening.")  With sheet composting you can bring soil under cultivation without actually having to dig it up.  It works particularly well on sod, as I had in my little pathway: the sod does not have to be removed or killed back before a ground cover can be planted.  The newspapers topped with cardboard stops the weeds and grass from growing, depriving them of light and air, and so choking them back to die.  The weed/grass roots and tops decompose in place, adding significant organic matter to the soil.  The sterile planting medium above the weed-barrier layer allows plants placed in it (the Angelina sedum) to get a good start with no weed competition.  Unlike a situation where the soil is tilled, there are no weed seeds brought to the surface to compete with the stuff the gardener actually wants to grow.

The newspapers and cardboard eventually decompose (I'd expect that by next fall, all the newspaper and cardboard will have disintegrated). The pro-mix, too, will decompose--all organic matter does, and the pro-mix is mainly organic.  I'd expect it to be pretty much gone by the summer after next (summer of 2014) at the latest.

As a result of all this decomposition, the level of the medium will drop.  However, by then, the sprigs will have gained traction and will grow upwards--if the Angelina sedum runs true to form, this sedum will grow above the level of the pavers, leaving the pavers as islands in a sea of sedum. The look is charming, and quite suitable to a secondary path such as this one, although the charm would turn to annoyance if the path were a main one and one had to lift one's feet high with every step to avoid crushing the sedum.

Even when the medium has rotted away completely, so that the sedum has actually come to sink its roots down into the original soil, I would still expect the sedum to grow to a level above that of the pavers. I expect this will happen for three reasons:
  • First, even when the pro-mix and cardboard and newspaper breaks down, the bark nuggets will remain for years.  Bark has a substance in it (lignum) which breaks down much more slowly than ordinary wood
  • Second, the sedum (like any thickly planted perennial) adds organic matter to the top soil level, such that the soil level rises over time. In other words, although the pro-mix, newspapers and cardboard all shrink and decompose, I'd expect the soil level itself to swell and grow due to the additions of organic material at its surface from the sedum shedding leaves, growing new roots, thickening up, etc.  
  • Finally, even if the sedum were not part of the equation, pavers will sink steadily into the ground--in my experience, even quite a thick paver simply laid on sod or even bare soil will eventually sink so far into the ground that it becomes level with with the ground's surface, if not actually half-buried.  I'm not sure what the mechanism is here, but I think this is why archeologists dig into the ground to find evidence of the past--the ground simply rises up over time. 


Naturally, weeds will find their way into this system at some point--some hardy runners may survive under the sheet composting, particularly along the edges where the newspaper leaves a gap.  Further, new weed seeds are blown in all the time, ready and willing to take root in the nice, soft medium at the surface.  However, that same nice soft surface ought to make the weeds  pretty easy to root out, especially if I keep after it and don't let them get big until such time as the Angelina can thicken up to do the job all on its own--probably by the middle of summer 2013.  Also, Angelina is a very distinctive- looking plant, and weeds are easy to see in it (which is one reason I chose it as the groundcover for this pathway project).

Here is a photo of the path to this point: you can see the sprigs of Angelina sedum in the planting medium.

Round pavers with Angelina sprigs in planting
medium, bordered by limestone blocks
2014 addendum: A new post shows this path after two years, and expands this idea, showing a perennial flower-bed established in this same no-dig sheet composing manner.

1 Comments:

Blogger Mike Carter said...

Thanks so much for sharing this. I recently got my backyard redone and had to get some concrete pavers in order to finish the big project. I had something similar done with my yard, and it looks great.

April 24, 2013 at 5:20 AM  

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