The answer to 'why is my hedge mud' is that your hedge is likely becoming waterlogged due to poor drainage or excessive rainfall. This can cause the soil around the hedge to become saturated and turn into mud. Symptoms include the hedge looking unhealthy, with leaves wilting or turning yellow, and the ground around the hedge becoming spongy or puddling with water.
To fix a muddy hedge, you'll need to improve the drainage in the area. This may involve installing drainage pipes, building up the soil with compost or gravel, or reshaping the landscape to direct water away from the hedge. In some cases, you may need to transplant the hedge to a better-draining location. If the problem persists or you're unsure of the cause, it's best to consult a professional landscaper who can assess the issue and recommend the appropriate solution.