The answer to 'why is my drainage system weeds' is that weeds can often grow in drainage systems due to the moist, nutrient-rich environment. Weeds may take root in the soil, gravel, or other materials used to construct the drainage system, and can clog the pipes and prevent proper water flow.
Common causes include inadequate maintenance, poor initial installation, or changes in the landscape that alter the drainage patterns. Symptoms may include standing water, slow drainage, and visible weed growth in the system. To address this, you'll need to clear out the weeds and debris, inspect the system for any damage or blockages, and consider making improvements to the design or maintenance routine.