>> My patch under trees in moderate shade died out. But the ones in full sun seem to do great for years
That sounds like my problem. Too much shade (and maybe tree roots).
>> these have been given a topdressing of compost every year x 4 years.
And my other problem. I have more beds than I have compost, so only the most valued beds get compost. All the beds were happier when I filled my car's trunk with bagged manure/compost mix several times per year - I had better go back to doing that.
