| By William Scheick
Contributing Editor |
This was our situation. After several years of record-setting drought and triple-digit temperatures, our tree-canopied backyard in Central Texas had begun to revert to its original Mars-like stony terrain, where barely even weeds could grow. It wasn’t just our years-deep gardening vision — lily-turf groundcover, shade trees and fence-line border plants thriving in dappled settings — that was eroding. Increasingly worn away by wind, water and foot-traffic, the sun-baked and heat-desiccated powdery earth itself was literally disappearing. Our backyard was sinking before our eyes. Soil erosion had to be stopped, the trees rescued and our peace of gardening-mind restored.
Once again my wife Catherine and I thought about installing an automatic watering system. But it was a bit late in the game for that, not to mention that our rock-and-boulder and (now) tree-rooted landscape would present considerable challenges to belowground installation. We were aware, as well, that at this point in time run-off from any watering system could contribute to ground-erosion in our sloped backyard. Nor could we ignore citywide water rationing, with expensive utility-pricing tiers. Although the ever-growing number of Austin residents somehow managed to reduce their water consumption by 17 percent per person between 2006 and 2013, from 2006 to 2014 their water rates had nonetheless surged by 123 percent. City predictions currently indicate an additional 31 percent increase during the next few years, not to mention the looming threat of officially predicted new “drought rates.” In fact, even as we were considering how to address our yard-situation, the Austin Water Utility department was forecasting a stage-3 citywide ban on automatic watering.
Whatever we decided to do, we had to keep in mind that our backyard had “impervious cover limits” designed to protect the Barton Springs Edwards Aquifer. These limits (which we support despite probably being “grandfathered”) meant that most of our new interventional landscaping project should permit rain to get into the ground, where it could seep downward. Even without these restrictions, the sheer number of the widespread tree roots we were trying to aid would require that most of our project would have to remain pervious to water.
GETTING STONED
Since our backyard groundcover of lily turf and mundo grass had (after a long successful “run”) mostly failed during the drought and heat of recent years, we turned now to inert groundcovers: tons of river rock, cut limestone, retaining-wall blocks, patio stones, pavers and pea gravel. Most of these materials would (as needed) have to be delivered to the front yard, the rest managed with our pickup truck. We were looking at months of labor ahead and we were weighing strategic issues, such as managing the substantial drop-off (slope) in our backyard, which at one point (by the glasshouse foundation) formed a steep natural rain sluice. Perhaps the hardest trick to pull off would be for Catherine to figure out how to combine these very different materials into an overall attractive pattern.
Just as I had partitioned the yard into imaginary sectors for our first pre-tree landscape intervention many years ago, once more I found myself planning our project in portions. The easiest part to imagine stretched from side-fence to side-fence along a roughly horizontal line that included a raised peninsula created by a limestone wall I had built previously. This targeted area also encompassed the space beneath the porch ramps and ran parallel to the entire back wall of the house. A dozen or so feet from the house we positioned limestone blocks in a curved pattern. These would serve as a retaining wall, an edging accent and also our first step-down device to accommodate slope. We covered the ground between this limestone barrier and the house with good-sized river rock.
River rock is pervious to water but not easy on feet or paws. So Catherine came up with a design using foot-friendly, interlocking “Canyon Patio Stones.” Starting at the bottom of the back-porch ramp, these patio stones would run rightward (to the yard gate) and leftward (to a fig tree and a spacious fenced-in dog compound). No cement or mortar would be needed, only water-pervious decomposed granite for interfacing the heavy patio stones surrounded by river rock.
The other, even larger side of the retaining limestone margin was more challenging to plan. During our first landscape intervention we had “built up,” but those mounded border and outlier berms had proved inadequate against the latest Central-Texas weather patterns. We decided to build still higher, though not as problematically high as the Tower of Babel. We settled for a large centered plant island made up of stacked (un-mortared) curved retaining-wall blocks to be capped by a single layer of mortared “Old Town Blend Holland” pavers. This island would be completely open to sunlight from its southern side and it would be filled with a huge amount of good dirt.
The plant island required time to configure and construct, but the last stage of our stonescape project was much harder. Catherine chose 16” × 16” yellow “Belle Cobble Concrete” pavestones (attractively scored with concentric arcs) that she arranged (in un-cemented units of four) around the plant island. Each of these units alternated with open-cell squares that were margined by the “Old Town Blend Holland” pavers similar to those topping the retaining-wall blocks of the plant island. We then filled these margined open-cell squares with colorful pea gravel.
Keeping everything level, maintaining the running pavestone pattern (four joined squares or appropriate fractions thereof) and managing the occasional “step-down” to compensate for slope presented us with some challenges. Even so, the only place we had to use a little mortar was around the base of one lacebark elm where the eroded ground angled down too much for us to do otherwise. In a few places, usually to manage drop off, I hammered into the ground either landscape pins or upside-down galvanized hurricane ties to keep some pavers from moving out of position.
STICKS AND STONES
Our second backyard intervention was finished in 2012. We do not know, finally, how much money or time this project took. Let the phrase “a lot” suffice. We preferred not to anticipate exactly what the project would require but, instead, kept to our usual practice of just starting and then making headway until a project is completed. Our result won’t appeal to everyone or qualify for an HGTV profile, although I will mention that I lost weight and achieved a lower LDL cholesterol score.
2013 was another record-setting year for Central-Texas drought and heat, amounting to (according to the Austin Water Utility department) a situation worse than the decade-long drought of the 1950s. According to the Lower Colorado River Authority (LCRA), 2013 was the seventh consecutive year of drought, marked by the second-lowest river- and stream-flow into the Highland Lakes.
Nevertheless, during 2013 (unlike previous recent years) the newly “stoned” trees in our backyard did not shed leaves and twigs. There were no broken limbs, and the “stoned” trees and bushes continued to look vibrant throughout the summers of 2013 and 2014. Our widespread stonescape, it has turned out, is the ideal mulch for our trees. It has kept tree roots cooler and protected them from soil-erosion by foot-traffic, wind and water. The stonescape has also conserved water by minimizing moisture-loss by wind, run-off and evaporation. Moisture clings to the stones and slowly seeps around them and through the seams of adjacent pavestones to enter the ground. The trees have even sent tiny roots upward to touch the stones, especially the pea gravel.
While our huskies no longer track grit and mud into the house, we do still have some weeds to manage, more so in the river rock than in the pea gravel. At the outset of the project we had not attempted soil solarization over such a sizeable project-area of already dehydrated and compressed soil. This technique of using black plastic and sunlight to exterminate grass and weeds also kills covered tree roots and crucial beneficial soil bacteria. As an organic technique, in my opinion, soil solarization works best in small spaces that can easily be brought back to life by adding compost and other additives.
I had already learned plenty from others’ efforts to prevent weeds from sprouting beneath their hardscapes. There’s black landscape fabric, the expensive kind that the pros use, which seems to work fairly well for the most part. Some inventive homeowners had tried shower curtains, vinyl tablecloths, pool liners and even carpets beneath their river rock. None of these approaches help tree roots. And rain from “sky flushes” — those brief but incredibly intense downpours that have deeply rutted our neighbors’ unmanaged backyards — pool in these impervious weed-blockers and wash the rocks out, occasionally moving them into the street as far as a block away. Layered newspaper is more pervious, but only works for a short while as a weed blocker and, once saturated, actually serves as a seed-starter medium.
Actually, since so much of my southwardly exposed backyard had already been naturally solarized by sun-scorch, most of our stonescape weed issues have come not from below but from above. No underlying weed-blocker can stop the germination of avian- or wind-borne seeds finding a wonderful haven in the damp, cool, shady clefts between the rocks and pavers.
The lovely trees we saved by installing a rockscape became the chief culprits in spreading seedlings among the stones beneath them. Opportunist elm seeds take hold quickly, sending roots quite deep while still out of sight among rocks and stones. By the time these seedlings appear, they are nuisances. That’s the bad news. The good news is that even when nearly a foot long, elm-seedling roots are not widely branched. So these plants can be entirely extracted by hand, one at a time (unfortunately), after a substantial rainfall.
A SPECKLED ROCKSCAPE
So I weed, and most interlopers pull free easily enough and (with the notable exception of trumpet vine and henbit) don’t return. Actually, I have become more laidback about a rockscape dotted with some low-to-the-ground green here and there — a mixed-media artwork, as it were. I am reminded of a story, told by Benjamin Franklin, about a man who wanted an ax head polished perfectly on both sides. He hired someone to undertake the difficult task, which then stretched on interminably. The would-be perfectionist ax-owner, frustrated and impatient, eventually was willing to accept the tool as it was. “I think I like a speckled ax best,” he finally told the worker — and himself. Me, too, I think: I have come to like my green-speckled rockscape just fine. I can live with it being less than perfect.
I am not quite at that point with the plant island, however. Building even higher was an improvement, yet results have remained mixed even with good soil, mulching and watering. I had opted for ‘Knock-Out’ roses for the four outer island-loops, while in the island itself I planted a variety of vertical-type plants, including various ornamental grasses. In 2013 the grasses in particular sputtered and then went prematurely dormant by end of July. In 2014 various cultivars of Miscanthus sinensis performed reasonably well, whereas (surprisingly) purple fountain grass (Pennisetum setaceum) barely re-sprouted.
After gorgeous spring displays, the ‘Knock-Out’ roses become leggy and almost leafless during the worst part of summer, when they also stop blooming. But they live up to their reputation as a Texas Superstar by rebounding quickly and bursting out in flowers by mid-October. The other highly successful island plants include clumps of foot-high ‘Emerald Goddess’ lily turf (Liriope muscari) and African iris (Dietes bicolor), both stalwart evergreens that have remained vibrant and have also bloomed despite ravaging weather.
All of the rescued backyard trees are deciduous — a plus during winter, when their lack of foliage allows for maximum light and warmth while the sun hugs the southern horizon. Leaf-shedding trees meant, however, that we had to overcome our aversion to leaf-blowers. A leaf-blower became essential for cleaning up autumnal debris from our rockscape. We considered user-reviews and selected an inexpensive and lightweight top-choice electric blower. It has worked perfectly. Sometimes, too, a little of the pea gravel needs to be swept off the pavestones and back into their paver-margined cells.
I am still thinking about how to get the plant island to look more like my ideal image of it. I remain fairly hopeful about some of the grasses in possibly more clement future years. The margins along the stoned fence-line and in the dog-free area also need more attention. But whatever we decide to do about these matters, that work will be easy compared to the two interventions that have gotten us to this point in our backyard. As for the trees, for now (at least) they have been rescued and continue to grace our yard with their priceless shade and majestic beauty.
