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Norma Series

If you live on Alderwood soil, there is a good chance that Norma soil is somewhere nearby, sitting in the low spot where water collects. This is one of the most common soil pairings in Puget Sound residential neighborhoods: Alderwood on the slopes and ridges, Norma in the depressions and drainageways between them. The water that runs off the dense layer in Alderwood has to go somewhere, and it flows downhill into the low spots where Norma formed. Norma is poorly drained, but it has one advantage over the other poorly drained soils in this region: volcanic ash. The surface horizon contains ash from ancient Cascade eruptions, and that ash gives the soil better nutrient-holding capacity than you would expect from a wet, low-lying soil. Soil scientists call this an aquandic property. In practical terms, it means the topsoil is darker, more fertile, and more responsive to organic matter additions than comparable soils like Bellingham or Briscot. The texture is ashy loam in the upper layer over sandy loam below. The sandy loam subsoil is actually a hidden asset: once water is managed at the surface, the subsoil drains reasonably well. This makes Norma more fixable than soils like Woodinville or Bellingham, where the fine texture persists all the way down. For gardeners, the key insight is that Norma soil sits where water naturally collects. You cannot change the topography that sends water to these spots, but you can work with it. Rain gardens, French drains to intercept slope runoff, and raised beds for plants that need drainage all work well here. The volcanic ash in the topsoil gives you a better starting point for fertility than most poorly drained soils offer.

Quick Facts

Texture Ashy loam over sandy loam
Drainage Poorly drained
pH Range 6.2-6.4 (slightly acid, which is a comfortable range for most landscape plants and vegetables without amendment)
Parent Material Old alluvium
Landform Depressions on glacial till plains and drainageways
Prevalence Moderate extent — MLRA 2 (depressions on glacial till plains)
Seasonal Water Table At or near the surface during the wet season (typically November through April)
Taxonomic Class Coarse-loamy, mixed, superactive, nonacid, mesic Aquandic Humaquepts

Key Challenges

  • Poorly drained because it sits where water naturally collects. The surrounding Alderwood slopes shed water off their dense subsoil layer, and it flows downhill into the depressions where Norma formed. You are not just managing the rain that falls on the Norma soil itself, but also the runoff from the slopes above.
  • Seasonal ponding is normal, not a sign that something is wrong. These depressions collect water every wet season. If your yard has a persistently wet low spot surrounded by better-drained slopes, there is a good chance you are looking at Norma soil.
  • Development grading often makes these spots worse. Builders working in Alderwood-dominated landscapes sometimes grade the low points without addressing drainage, placing foundations, patios, or lawns on Norma soil that will be wet for months each year.
  • The wet-season water table sits at or near the surface from November through April. Plants that cannot tolerate months of saturated roots will struggle at grade without drainage modification.

Amendment & Management Strategy

  • The volcanic ash in the surface horizon gives you a better starting point than most poorly drained soils. Organic matter additions are still valuable for improving structure, but you are building on a naturally fertile base rather than trying to create fertility from scratch.
  • Raised beds are the most reliable approach for vegetables and ornamentals that need good drainage. Even 8 to 12 inches of imported soil mix above grade puts roots above the seasonal water table and transforms growing conditions.
  • The slightly acid pH (6.2-6.4) is in the ideal range for most landscape plants and vegetables. Unlike Bellingham or Seattle Series soils, you likely will not need to lime.
  • Work with the topography rather than fighting it. These are natural water collection points, and the most successful landscapes treat the wet areas as features (rain gardens, native wetland plantings) rather than problems to eliminate.

Drainage Solutions

  • French drains positioned upslope to intercept water flowing down from Alderwood before it reaches the depression. This is often the single most effective intervention, because much of the water problem comes from the slopes above, not from rain falling directly on the Norma soil.
  • Rain gardens are a natural fit for these depressions. The site is already collecting water; planting it with species that thrive in seasonal wet conditions turns the lowest spot in your yard into an attractive, low-maintenance landscape feature.
  • The sandy loam subsoil is the reason drainage improvements can work here. Unlike Woodinville or Bellingham, where fine-textured soil persists all the way down, Norma has a subsoil that actually moves water once the surface drainage is managed.
  • Dry wells or infiltration trenches may work if the subsoil permeability is confirmed at your specific location. Because alluvial deposits vary, it is worth testing before investing in infrastructure.

Plant Suitability

Well Suited

  • Rain garden species like redosier dogwood, Douglas spirea, and native sedges, which tolerate both the winter wet period and drier summer conditions. These plants are specifically adapted to the fluctuating moisture cycle that defines Norma soil.
  • Western redcedar tolerates seasonal wet feet better than almost any other conifer in the region and is a natural choice for the wetter areas of a Norma landscape.
  • Native wetland-edge plants that thrive in the transition zone between wet and dry conditions, including salmonberry, red alder, and vine maple.
  • Raised bed vegetables and ornamentals, which bypass the drainage problem entirely. The good baseline fertility from the volcanic ash means less amendment is needed in the surrounding soil than on other poorly drained sites.

Avoid

  • Upland species planted at grade in undrained depressions. Plants that need well-drained soil will not survive months of saturated roots, regardless of how well they are established.
  • Mediterranean and drought-adapted species like lavender, rosemary, and cistus at grade. They cannot tolerate the winter wet period.
  • Trees with low tolerance for waterlogging, including most maples (except vine maple), most oaks, and most fruit trees, unless planted on raised mounds with drainage.

Official Source

USDA-NRCS Official Series Description

Native Tree Species

Western redcedar Red alder Bigleaf maple Western hemlock

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