Landscaping & Hardscaping in Sammamish, WA

Sammamish is a plateau, and almost every peculiarity of working here follows from that one word. The city occupies high ground between four hundred and five hundred and fifty feet, with Lake Sammamish below it to the west and the Snoqualmie Valley below it to the east, and steep drops on both edges. The ice sheet left the top of the plateau pocked with closed depressions, and those depressions are now Pine Lake, Beaver Lake and dozens of smaller wetlands that never drain anywhere. Ebright, Zackuse, George Davis and Laughing Jacobs creeks run off the west edge into Lake Sammamish and carry kokanee, which is why the stream buffers here are wide and taken seriously rather than treated as a formality.

The city is young and the neighborhoods are older than the city. Sammamish incorporated in 1999, but the bulk of the housing was platted under King County rules through the 1980s and 90s, which shows up in the details: generous lots, many of them a third of an acre to an acre, cul-de-sac layouts, and a builder practice of leaving stands of Douglas fir between houses. Those firs were forty feet tall when the plats went in. They are ninety now, and a great deal of what we get called about is the consequence. Sahalee and the Pine Lake area are the older end. Trossachs, Aldarra and Montaine are newer. Inglewood Hill runs down the west edge toward the lake.

Four complaints cover most of the calls, and they are all connected. The lawn will not grow, because the tree the builder left has closed the canopy and turf will not win that fight, so the honest fix is shade planting or hardscape rather than another round of seed. The back third of the property is a bog from November to April, because the plateau is till with a hardpan a shovel rings off and rain travels sideways on top of it until something intercepts it. The rockery or the block wall the builder installed in 1994 is bulging, because it never had drain rock, filter fabric or geogrid behind it. And the deer eat everything, which they do, and no repellent schedule survives contact with a Sammamish herd for long.

What the crew hits confirms all of it. Alderwood gravelly sandy loam over dense Vashon till, with hardpan usually somewhere between twelve and thirty inches, is the standard profile. Around the closed depressions the material turns to peat and organic silt where bearing disappears and a patio base has to be over-excavated and separated from the soft ground rather than floated on hope. The west edge above Lake Sammamish drops steeply and is mapped for landslide hazard, with seeps emerging where permeable material sits on the pan. In some 1980s plats we still find buried stumps and slash from the original clearing, which rots out and leaves a soft spot exactly where a wall footing wanted to be. Rainfall on the plateau runs higher than in the Kent valley, which just means more water arriving on ground that will not take it.

So we design the water first and the finish second. A Sammamish patio gets a base with a route for the perched layer instead of a dam across the slope, finish grade with real fall to a daylight outlet, and catch basins located where water already stands. Anything over four feet gets stamped engineering and geogrid tied into competent material, and tiered walls get looked at as one structure rather than two short ones. Fence posts frequently need an auger with genuine torque, and a post hole holding water overnight gets drain rock in the bottom instead of dry mix dumped into a puddle. For planting we choose things that tolerate shade, wet feet and browsing: sword fern, salal and evergreen huckleberry under the retained firs, vine maple and rhododendron for height, carex and red twig dogwood in the corner that will never dry out, and lavender, hebe, kinnikinnick and dwarf conifers where deer pressure is heaviest. Irrigation on the plateau ties into Sammamish Plateau Water rather than a city utility, which has its own cross-connection and backflow testing requirements, and every system we install gets an assembly, a test and a fall blowout. Design is drawn in-house and our own crew builds it, so the grading that was worked out on paper is the grading that gets installed.