How to Make a Flower Bed Border Around a Tree on a Slope

Lay out your intended flower bed with a border of decorative rocks or bricks. This border defines the bed visually (and to visitors) and helps to contain soil on the low side of the slope. Set the rocks or bricks firmly into the soil to keep them steady, digging a shallow trench if necessary to help them stay in place. Stack the bricks or rocks as high as necessary to to make the front of the bed level with the back of the bed to contain soil and prevent erosion. Line the inner side of this wall with fine mesh to further prevent erosion on the slope.

Amend the soil throughout the bed before planting. Turn over the top 6 inches of natural soil with a shovel and level it out. Leave at least 6 to 8 inches of space between the back of the annual bed and the tree's trunk to give the tree room to breathe. Pull out rocks and weeds to give the annuals the best planting base. Mix 7 to 8 inches of organic compost, peat moss, leaf mold, rotted manure or wood chips into the soil. This amendment gives the soil better nutrition and drainage, with good long-term moisture retention. The addition of more organic material builds the soil up and prevents interference with tree roots. Turn 5-10-10 or 5-10-5 fertilizer into the soil.

Plant like-minded annuals throughout the bed for immediate impact. Choose sun-loving annuals such as begonias, marigolds, daisies, posies, pansies, petunias and vinca for the sunny spots, and shade-loving annuals such as primroses, violets and forget-me-nots for the shaded areas. Watch the way sunlight filters through the tree's branches and hits the slope at its base for an entire day before choosing plants to ensure you select varieties that will thrive.

Mulch the soil around the plantings with rock or organic amendments to keep the soil in place and prevent surface erosion during rainstorms. Mulch also maintains soil moisture and keeps the plants warm during the cool seasons.