Interesting--I have some seriously aggressive and competitive (downright weedy) thymes, blue star creeper, and sedums so I am having a hard time imagining their demise where the others thrive.
Is this sun or shade or some variation?
What is the soil like?
Could it be too much water/poorly drained such that they rot before they establish? (I am too tired to figure out if Stanwood is a rainy part of the PNW or not--it's all much more rain than I can relate to. Plus, and "landing area for my water faucet" has me wondering the same.)
Are you trying to plant something with lots of existing roots into these spaces?
It could be that if you remove the 'weeds' that you don't want that you could then try seeding the cracks with the 'weeds' you would prefer--and see better results.
I often find the most amazing volunteers growing in my sidewalk cracks
Alternatively, you could try rooting little spriglets or rosettes into the spaces (that works very well with succulents), but again you'd have to clear the competition.
Same idea really--plants that send their own roots into spaces where we can't exactly 'plant' them will regularly grow into themselves and establish very well despite our perception of poor conditions.
I'd be happy to suggest some additional indestructible-for-me-anyway ground covers with a little more info to guide my suggestions.
