Few plants live forever. There are plants that can and do live for several thousand years and it is not uncommon for many tree species to survive and flourish for over 1000 years. Many shrubs can live for 100 years, or even longer. Most, though, live for far less. Some shrubs are more noticeably short-lived than others; Ceanothus would be a good example here.
Ceanothus, or Californian Lilacs as they are commonly known, are handsome evergreen and deciduous (mostly) blue flowered shrubs from North America. Some are groundcover, while others can become the size of a small tree. Most are blue flowered, though pinks and whites also exist. They grow and mature quite quickly with some of the 40-50 species and many more varieties being capable of achieving 4m (12’) in just 5-8 years. Unlike many larger shrubs, their lifespan is pretty short with most typically living between just 8-12 years in the UK.
I have seen plants live for 15-20 years, but it isn’t that common and most succumb at around a decade.
Over the years as a designer and garden consultant, easily the most common question that I have had about Ceanothus has been, ‘Why did my Ceanothus die?’ It is almost always followed by, ’I don’t understand why it, as last year it flowered better than ever!’
This is common enough, with many plants having a ’Swan Song’ year where they do particularly well in an effort to produce the most possible viable seed before expiring. Ceanothus often do this and a bumper flowering year on older plants may be a cause for concern.
My best advice here is have a backup plan. Expect your older Ceanothus to fail and perhaps have a plant growing elsewhere in your garden in a large pot ready to fill the gap. I’ve recommended it to garden owners before and it has proven to work brilliantly at minimising the visual disruption of losing a big shrub.
Food for thought.