Working the Angles, Techniques for Gardening on Slopes
Stop mowing that steep slope and fill the space with colorful blooms.
But planting on steep slopes like this can be difficult and soil erosion is a major concern. An old pot cut in half and a planting trick can keep your plants and soil in place. Dig a hole straight down into the hillside and large enough to accommodate the half pot. Fill with soil and plant your flower at the proper depth. Its been working here for several years.
Use drip irrigation or this nifty watering device to slowly provide needed water without washing out the soil. And dont forget to mulch.
A bit more information: Converting a hillside from grass to a garden can be challenging. Once the existing plants are killed and removed the hillside is subject to soil erosion. You can avoid this problem. Kill the grass with a total vegetation killer that allows you to plant within several weeks. Leave the dead grass in place to stabilize the soil. Plant through the layer of dead grass and cover the surface with mulch. The dead grass layer helps hold the soil and fibrous mulches in place and provides additional weed control. The dead grass will break down over time, adding organic matter and improving the soil to help your plants grow.