Sheet: L-5.1
Subject: Ground conditions — Hillsboro
Locality: Washington County

Landscape design and build in Hillsboro.

Some of the best agricultural soil in North America is under Hillsboro. On a lot of newer lots, it is no longer under your garden.

Rows of young shrubs in black plastic nursery pots standing close together on the ground at a growing nursery, each perhaps two feet tall with thin new growth. — The size most things arrive at. A small plant overtakes a large one inside four years and costs a third as much.

Woodburn and Willamette silt loam, in theory

The Tualatin plain carries deep, fertile, well-structured silt loam. It is farmed for a reason. If you have an older property in town or out towards Jackson School, you may genuinely have three feet of it, and it is a pleasure to work with.

If your house was built on former farmland in the last twenty-five years, the position is often the opposite. Topsoil is a commodity. It is routinely stripped and sold before the foundations go in, the lots are graded and compacted by heavy plant, and then a thin skin of screened material is spread for the sod.

So the answer to 'is the soil good in Hillsboro' is: the soil is excellent, and there may be none of it left on your lot. Those are not the same statement, and only a hole in the ground can tell you which one applies.

Flat, and compacted rather than naturally heavy

Where a new-build lot drains badly it is usually compaction rather than clay, and that is better news than it sounds — decompaction and deep organic matter genuinely change the behaviour of a compacted silt loam, which is not something we would promise you in Lake Oswego clay.

Deer

Low in town. Real out towards Rock Creek, Bethany and the western edge, where new subdivisions back onto open ground and the deer were there first.

The lots

Newer subdivisions run tight — five to eight thousand square feet, houses close together, and often a strong prevailing orientation across the whole street. Orenco and the older parts of town have more room and more mature canopy to design under.

Watch for

The soil survey for the field next door tells you nothing

Homeowners here often look up the county soil map, see a first-class agricultural classification, and reasonably conclude the soil is fine. The map describes what was there before the grader. We dig test pits on every Hillsboro job for exactly this reason, and the result changes the budget in both directions — we have found beautiful ground under a 2019 build, and we have found nothing at all.

If you are on a newer lot and nothing has thrived in five years, it is worth knowing what is actually down there before you buy another round of plants.

Start a design What grows here Call (503) 555-0147