I live on a pile of glacial till that was scraped from northern Canada and ingloriously deposited here during the Pleistocene glaciation that shaped Puget Sound. Some areas are gravelly/sand topped with rich forest loam, but much of the property is heavy clay loam or even pure clay. I’ve no lush Puyallup Valley riverine loess here, just clay and clay and more clay.
But the pity party is over: In the developed areas around the buildings, I’ve been diligently working to renew the soil through mulching with mushroom compost and decomposed horse manure where I can afford it. I buy soil and create piles where the soil is too compacted to manage, and I just mow the rest.
I’ve killed a lot of plants, many of which I bought on the cheap as is my custom. Here are a few that have stuck with me for the duration and the places where they’ve survived:
Beauty bush (Kolkwitzia amabilis) - grows in full sun on a mound of heavy clay soil with little amendment
Witch hazel (Hamamelis x intermedia ‘Jelena’) – grows in full sun on sandy loam mixed with some decent topsoil. Slow growing but appears healthy.
Double-file Viburnum (Viburnum plicatum var. tomentosum ‘Mariesii’) – grows in full sun on a mound of heavy clay soil with little amendment. Gorgeous plant that has grown to over 6 ft from a one gallon pot in four years.
Penstemon sp. – I’ve lost track of which species I now posess, although Penstemon ‘Blue Midnight’ is among them. They have all done very well in full sun/clay soil with one achieving a height of three feet.
Blue holly (Ilex meserveae) - full sun and heavy clay soil right next to the Weigela. Slow growing and still wider than tall but a survivor with about zero maintenance. And the deer won’t touch it.
Day lilies (Hemerocallis sp.) – a rather common looking sister with yellow flowers that I inherited from my mother. Give it sun and it will grow anywhere. Without sun, it will survive in a grass – like state but not bloom. Get large fast and easily transplanted.
Highbush cranberry (Viburnum opulus) – needs damp, organic soils and absolutely loves nurse logs/stumps.
The viburnum in front of the barn has done spectacularly with full sun and a cedar stump for a base. In shade or hard, rocky soils that dry out in summer, it survives but grows so slowly as to be nearly unnoticeable. I’ve some that have remained the same height for three years.
Shasta Daisy (Leucanthemum x superbum) - grows anywhere with a bit of sun. Invasive in my garden, it freely reseeds. I am actually trying to find places where it won’t grow.
Situationally dependent -
These things appear to detest rich soils even if the sunlight is good. The thymes thrive for one year, then die the next, while the rosemary and lavender languish with half of their branches bare. My amendments may have to include more rock and sand than organics.
What not to put in a damp, shady area with clay soils:
Monkey flower (Mimulus sp.)
These have all been complete and utter failures in the ditch that was hoping to transform into a water garden. It was dug down to the clay level, and the banks are sodden in winter. None of these plants lasted a season. Even the red osier dogwood has declined to grow more than an inch or so in the three years after placement on a damp bank.
I’m considering a load of gravel topped with an organic soil.