The answer to 'why is my stone walkway overgrown' is that the most common causes are lack of regular maintenance, excessive plant growth, and improper installation. Over time, weeds, grass, and other vegetation can creep into the cracks and spaces between the stones, causing the walkway to become overgrown and unsightly. This can happen due to poor drainage, insufficient weed control, or the walkway not being properly edged and contained.
To resolve an overgrown stone walkway, you'll need to address the root causes. This may involve removing the excess vegetation, re-edging the walkway, improving drainage, and applying a weed-prevention treatment. Depending on the extent of the overgrowth, this may be a manageable DIY project, but for severe cases or if the walkway needs more extensive repairs, it's best to call in a professional landscaper or hardscaping specialist.