With a little preparation and planning, you can grow as many flowers on a slope as you can on flat ground. It is important to prevent soil erosion on sloped flower garden beds. You can prevent this by created a terraced bed, using rocks as a border. Another way to help prevent erosion is to plant shrubs, which generally have spreading root systems. You can also plant ground cover between flowers to help retain soil.
Select the area where you will plant your flower bed. Using a mallet, drive a wooden stake into the ground at each corner to mark the area.
Lay out rocks along the front and sides of the beds. Select large rocks for the first layer, and stack a second layer of smaller, flat rocks on top of the first layer. Stagger the joints between the rock layers.
Dig down into the slope directly above the rocks to back fill them with soil from above and create a level flower bed. Work the soil with a garden fork to loosen it. Remove any sod and weeds from the soil as you are working it with the fork. Pull the stakes out of the ground.
Mix compost with the soil, using the garden fork. Dig holes for your plants in rows along the flower bed. Space the holes according to the mature plant spacing requirements. The rows will help retain water allowing it to gradually drain from the bed. Select a mixture of perennials and annuals to create a varied flower bed each year. Add in shrubs to help prevent soil erosion. Shrubs and taller plants should be planted along the back of the bed.
Fill in around the plants with soil after you place them in the holes, and pack the soil down gently with your hands. Fertilize around the plants with 5-10-5 fertilizer immediately after planting and then twice more at six-week intervals. Water the plants after you have fertilized them, using a watering can.
Mulch the flower bed to help retain moisture and prevent weed growth. Keep your flower beds watered so that the soil is moist, but not overly wet.