The answer to 'why is my drainage system weeds' is that weeds growing in your drainage system is a common problem caused by blockages, poor design, or lack of maintenance. Weeds can clog up drains, prevent proper water flow, and lead to water pooling and other issues.
Symptoms of a weed-clogged drainage system include standing water, slow drainage, and weeds visibly growing in the drains or around the outlets. To solve this, you'll need to clear out the weeds and debris, then take steps to prevent future weed growth. This may involve flushing the system, installing weed barriers, or making adjustments to the drainage design.