Well, I'm nearly done with another, and am proud of the dry stone wall I used to terrace the bed to mitigate the slope of our front yard:
[image credit Gary]
The wall is about 2' high at its highest. The stones are all local limestone (Franklin County, PA is almost inundated with the stuff) that I snag from farmers' fields, their rock piles, wooded areas, etc.
Some of the largest stones came from the foundation of a particular nearby barn that was destroyed by fire. I made a number of trips gleaning rocks from that source, and some of them still bear the whitewash that was used on the inside walls of the barn. In my wall I made sure to place those stones prominently and not to cover up the whitewash, so I will remember that these stones were once part of a barn and now have a second life in my wall rather than being bulldozed for fill.
The link to Ultrarunning is that whenever I run I am on the lookout for wall stones. When I find a decent rock, meaning having at least one flat side and say up to the size of a microwave, I pull it to the edge of the road and go back for it later in my pickup. When I use the example of a microwave, a stone much beyond that in size I simply cannot lift because this particular geologic formation, the Chambersburg Limestone, is quite dense, checking in at approx 166 lbs per cubic foot.
I've done a bunch of dry stone walls in my life, and the two main "secrets" I've learned:
- Stagger the joints (for strength and better appearance)
- Lean the wall inward 10-15 degrees to compensate for the outward hydraulic pressure of wet soil
Bear with me for some simple physics. Since dry topsoil weighs approx 2000-2500 lbs per cubic yard--that's better than a ton, people--imagine its weight when it gets wet. There is enormous pressure against the inside of your wall, trying to force it out. You equalize the game in two ways: by the sheer volume, bulk and weight of your wall stones (the bigger, the better) and by the inwards lean.
Oh, and one other tip that I forget to include in my previous post, but it's relevant here: when you mulch, go deep. I use shredded bark that I get by the truckload, and I go at least 4" deep. The mistake many people make is to scrimp on the mulch, going only an inch or two deep...then wonder why they get weeds.
The tradeoff is more upfront costs versus ineffective coverage.