Self-seeders - friend or foe?

One of the many small joys of gardening is to discover that a treasured plant has set seed and produced a baby without any of your intervention. Some plants are so successful at self-seeding that they can become a nuisance, but I'm a firm believer that one person's invasive plant is another's good do'er. Let me share my experience with you and you can decide.

 Campanula latifolia (giant bellflower) forms tidy rosettes of narrow leaves and produces tall, thin spires of white, or sometimes blue, bell-shaped flowers. It like full sun or part shade, and slots in neatly between other plants. A very useful and pretty self-seeder.