A slope creates two different design questions: how to keep the soil covered and how to maintain it. A patch may support grass but still be awkward to mow. Start with the whole route from the top of the slope to the place water collects.
Find the source of the flow
Maryland Extension identifies erosion and compaction as soil problems that require attention to site conditions. Mark bare soil, channels and water arriving from a roof or paved surface. A seed purchase alone cannot solve concentrated runoff. Record photographs before changing anything.
Test small watering adjustments
If irrigation runs downhill before it penetrates, compare a shorter cycle with a pause to allow soaking. The useful schedule depends on the soil and system. Watch the lower edge as well as the upper part; more time can mean more runoff rather than more useful water.
Choose a maintainable surface
Check the mower manufacturer’s slope limits and operating instructions. Where mowing is unsuitable, plan a locally appropriate planted area or get help designing the slope. Before installing erosion materials, confirm they suit the gradient, establishment method and wildlife setting. For a steep or actively eroding site, a professional assessment is more useful than an improvised retaining structure.
Do not redirect runoff toward a neighboring property or a building to rescue a lawn patch.