DryStoneGarden

Failed Moss Rock Wall

In light of all today’s talk about tearing down that (Berlin) wall, here’s some photos of the biggest wall to come down in my neighborhood this past winter, when a section of hillside pushed a moss rock retaining wall into the road. Must have been a shock to the homeowner and whoever built it (not me).

Though, without sounding like I’m piling on the unfortunate builder of the wall, it was predictable that this wall would fail. A three foot high wall is supposed to be two feet thick at the base, and this wall isn’t even one foot thick. It also doesn’t have a proper foundation or gravel backfill. I see a lot of failed retaining walls around town, and the common denominator is that they are always backfilled with dirt instead of the drain rock or rubble that virtually every book or manual recommends.

Failed Moss Rock Wall

Intact Section of Wall

The wall is still intact where the bottom course has bigger rocks and the rocks are toed in against the curb.

Failing Section of Wall

Failing Section of Wall

Moss Rock

Two more waller nightmares are below. (more…)

Pack Mules on Duck Pass Trail

The topic for this month’s design workshop at Gardening Gone Wild is dealing with slopes. The description mentions “tips for building steps and paths to make slopes easier to navigate,” so I thought I’d cite the source I learned from, the forest service Trail Construction and Maintenance Notebook, which is online and in the public domain (Who owns this government document? We do!). The text might have a few elements geared towards public trails rather than residential gardens, but the diagrams are good and the principles are solid.

Step Construction

‘Build stairways from the bottom up, at a break in the grade. The most common mistake is to start part way up a grade. If you do so, the trail will wash out below the stairs. The bottom stair should be constructed on a solid, excavated footing. If it is constructed on top of exposed rock, it should be well pinned to the footing. Each successive stair is placed atop [or against] the previous stair. Dry masonry rock stairs usually rely on the contact with the stair below and with the footing to provide stability.

‘Hikers, especially backpackers, generally don’t like steps and will walk alongside them if there is any opportunity. The steps need to be comfortable to climb or they won’t be used. This means keeping the rise a reasonable 6 to 8 in (150 to 200 mm) and the run long enough to hold a hiker’s entire foot rather than just their toe. It’s helpful to armor the sides of steps with rocks to encourage users to stay on the steps.’

Stepping Rock and Riser Stairways

‘The most important area of the step is usually in the run. This is where most traffic steps as it climbs. If the step is composed of something like a board on edge with fill behind it, then the traffic will step onto the landing. Almost all foot traffic descending the step will walk off the edge of the step. The top of the step (and landing) should be stable and provide secure footing. The edge of the step should be solid and durable. The face of each step should not contain a batter that creates a “face run” of over 2 in (50 mm) from top to bottom. This is particularly important as the rise of the step increases.

‘Steps with landings are a bit harder to secure in place because the stairs do not overlap. Each step can either be placed in an excavated footing and the material below the rise removed to form the landing of the next lower step. This is usually the most stable arrangement. Or the step can be secured on the surface and fill used to form a landing behind it. The material used to provide the rise does double duty as a retaining structure when the landing consists of tamped fill. These steps must be seated well to prevent them from being dislodged by traffic. For stock use, landings should be long enough to hold all four of the animal’s feet.’

Riprap Stairway

‘In more primitive settings, you don’t need a uniform flight of steps as long as the route is obvious and there is solid tread at each stepping point. In the Sierra, a cross between cobblestones and stairs, locally called riprap, is commonly used for this purpose.

‘If the stairway climbs straight up the hill, each step should be slightly crowned to drain water to the edges or slightly sloped to one side. When the trail traverses a slope, each step and landing should be slightly outsloped. Water should not be allowed to descend long lengths of a set of steps or to collect on or behind a step on the landing. A drain dip where the trail approaches the top of the steps is a good idea.

‘In all steps, the key is to use the largest material possible and to seat it as deeply as possible. Rocks should be massive and rectangular. On steps that traverse a slope, it helps to seat the upper end of the step material in footings excavated into the slope.’

Rock Staircase

Best practice for building a stairway these days, if the rocks are big enough, is to butt them against each other instead of on top of each other. That way it is possible to repair one of the steps without redoing the whole staircase.

Rock Staircase

It doesn’t say in the notebook, but I was taught to kick test every step. If the stone moves when you kick it, it isn’t solid enough. A bit of a shock, sometimes, to see someone kick the structure you just labored on, but the step is definitely going to get kicked when people use it, so you might as well find out if it is going to last. You want to feel confident that your stairs are safe. It’s scary enough the first time you see a mule train crank through a set of steps that you’ve built even when you know the steps are solid. There aren’t mules in residential backyards, but the foot of a 150 lb. person can easily impact with 300 lbs. of force, so the basic principle is the same. Steps should be strong.

Steps also need to be regular. The test is to walk up and down the stairway without looking down at your feet. If the rise and run are even, you shouldn’t trip or stumble.

Old Town Wall Steps

In the front country I usually don’t get to work with stones that are “massive and rectangular,” but I still kick test every step and walk the staircase with my eyes closed. This set of steps, built with a local sandstone called Old Town Wall, was a lot of work, getting the risers to all match and the stones all interlocked enough to stay in place. I was working for a designer who is a serious dry stone purist, so mortar was out of the question. I think the steps and cheekwall took me longer than the entire rest of the wall.

Mortared Arizona Flagstone Steps

When it’s up to me — though I’m a dry stacker at heart — I usually build steps with mortar, usually by stacking flagstone with a recessed mortar joint. I don’t think that method holds up in areas with heavy freezes and probably not if the steps are going to be used by mules, but it does well in Bay Area gardens. A before photo of these steps and another mule photo are below. (more…)

Bristlecone Pine

While I was out on the east side, I visited the Schulman Grove of Bristlecone Pines in the White Mountains. Bristlecone Pines are the famous “oldest trees in the world,” and, checking them out in person, I found they have a suitably amazing presence. They grow on a very dry, barren mountainside, sometimes with other plants — mountain mahogany, sage (Salvia and Artemisia), penstemon, thistle, paintbrush, lupine — but with the oldest ones growing in pure stands of gnarled, low-growing, ancient trees. There is a four mile loop trail that passes through the grove that has the Methuselah Tree, the oldest tree on earth at almost 5,000 years old, though it’s not disclosed which one is the actual Methusaleh, the forest service keeps its identity secret and doesn’t let anyone publish any photos of it. (There was an older one, Prometheus, but it was cut down by a scientist, and a NOVA program about the bristlecones claims that someone has found another one older than Methusaleh; the NOVA link has some cool interactive photos.) They are concerned that people would walk close to it and cause erosion, risking it health as erosion is apparently what eventually finishes these trees. They survive lightning strikes, pests, drought, etc., but in 5,000 years on the side of a dry, sandy mountainside, they’re going to see some serious erosion. Living 5,000 years, they’re not even on tree time, they’re starting to be on geologic time.

The most striking feature is how much dead wood they have. One 4,000 year old tree has a four foot diameter trunk with only a ten inch wide strip of living wood. And even after the wood dies, it doesn’t rot. Scientists have found wood that is 9,000 years old; they used the tree rings on these trees to calibrate the process of carbon dating, they are literally the standard by which we determine how old things are. Which makes sense, as there is something almost archaeological about the grove. Serious patience and endurance; these trees abide.

Bristlecone Pine

Bristlecone Forest

There’s a nice photo from the Schulman grove in photographer Rachel Sussman’s project the oldest living things in the world. She also has photos of redwoods, alerces, a 400,000 year old bacteria, an “underground forest,” and clonal trees like aspens where the genetic material is 80,000 years old. Bristlecone and redwood photos are always cool, but I think the best photos in the series are of the plants I’ve never heard of, the ones that are not visually impressive but have been unobtrusively living for thousands of years. (Hat tip: Studio G)

Another photo of a bristlecone and a few other old trees is at the blog for friendsoftrees.org.

— Somewhat off topic, but I feel like bookmarking the link, a slideshow of the world’s most famous trees includes a bristlecone.

Mountain Phlox, Linanthus grandiflora

It’s seeding time for California wildflowers. It’s mid-October and the recent rains have germinated the reseeders, both wanted and unwanted. We always start some in potting soil this time of year, so that we can direct seed the wildflowers we want and then use the potting soil starts to fill in any gaps where the direct seeding failed. One of the ones we’re starting this year, after a couple of years break, is Mountain Phlox, Linanthus grandiflorus. We started it in a couple of gardens three years ago and hadn’t really thought about it since then, but this year we noticed that it naturalized pretty well in those gardens and that it keeps blooming until quite late in the year; it can bloom until as late as September in a garden where it gets some supplemental water. Also, we saw a thick patch of it in the Botanic Garden at Tilden this past July, looking good when most of the other native annuals were done, and it made us want to plant some more of it.

Mountain Phlox, Linanthus grandiflorus, at Tilden

We also started California Wind Poppy (Stylomecon heterophylla), which we grew for the first time this past year, Blue Flax (Linum lewisii) which isn’t an annual but functions a bit like one, and Clarkia bottae. The rest of the wildflowers will just be whatever reseeds.

Striped Agave and Ceanothus

What do porcupines say after they kiss?

Ouch.

This is largest, spiniest plant I’ve ever transplanted. It had been planted too close to a path and had reached a point where walking in the garden required a delicate, sideways, dodging step to get around it. There was talk about consigning it to the green bin of life, and less serious talk about homegrown tequila or mezcal, but it had been the most striking element in this garden for years and it was much much cooler than anything else that could have been brought in to replace it. You can’t really come up with a better focal point than a large agave. So I agreed to try moving it.

It was kind of fun, actually; certainly more interesting than anything else I’ve ever transplanted. I wrapped it in burlap and wore two pairs of gloves, but the thorns pretty much laughed at that (local seller of succulents Cactus Jungle Nursery recommend using pieces of carpet when you move a cactus and if anyone asks you to move one of these agaves, “just tell them no”), though I actually got most of my pokes while I was cleaning out the pups growing all around it. 

The real challenge was the weight of the thing. I don’t know what it weighed, but it was much more than a hundred pounds; boulders seem easy to move in comparison. I couldn’t lift it, the only way I could move it was to grab the top of it and kind of leverage it around while my client’s landscape architect friend rather tentatively pried at it with a rock bar. He didn’t seem to find the process as charming as I did.

Fortunately, we were only moving it three feet, to the center of the planting bed; I don’t think I could have moved it much further.  We moved it in early October, which I think is a little late — you want it to heal and put out new roots before the cold and wet of the rainy season — but the plant didn’t seem to mind and it’s still looking healthy now, a year later. And if it grows a few feet wider and blocks the path again? Well…

Albizia cycleiferous

It’s tough to be a tree in Golden Gate Park. Hardly Strictly Bluegrass Festival was this past weekend. Ridiculously crowded and a lot of fun, as usual. Personal favorites were Doc Watson, Galactic, and an over the top version of ‘This Land is Your Land’ by Tom Morello and Steve Earle.

Metasequoia schwinnii