A new flower garden breaks up a monotonous stretch of lawn while adding color and texture to your landscape. Converting an old lawn into a flower garden requires planning and preparation, but when done correctly results in an attractive upgrade to your existing yard. Begin preparing the old lawn area the summer or fall before so it's ready to plant immediately the following spring.
Site and Layout
Most flowers require six or more hours of sunlight daily, so a location in full sun works best for a new flower bed. The site should drain well so water doesn't accumulate on the surface. The shape of the bed depends on your lawn layout, preferences and the location of automatic sprinkler heads where applicable. If you have sprinklers, site the bed so it runs off a separate valve than the rest of the lawn, because flowers typically require less water.
Annual flowers require replacement each year, while perennials will return year after year without replanting. Although you can combine annuals and perennials in the same bed, make sure they have similar light, water and fertilizer needs. Low-growing flowers like pansies (Viola spp., United States Department of Agriculture plant hardiness zones 4 through 9) work well in small border beds. You can combine flowering spring bulbs like daffodils (Narcissus spp., USDA zones 4 through 9) with summer blooming annuals so your bed changes with the season. Flower shrubs, like beebalm (Monarda didyma, USDA zones 4 through 9) can provide an anchor in the center of a larger bed or island garden when surrounded with lower-growing annuals or perennials.
Completely remove grass and its roots before planting your flowers, otherwise it may invade the flower bed. You can dig up most cool season grasses, but warm season grass has deeper roots and will grow back if you don't remove it all. Covering the garden site with black plastic or cardboard sheets for one or two months during the hottest part of the year suffocates the grass and kills it. You can also spray the lawn with an herbicide formulated for grass. Most premixed varieties are sprayed evenly over the lawn and take about two weeks to dissipate.
Testing the soil before you plant provides a guide for choosing amendments and fertilizers. Most flowers prefer neutral soil with a pH between 6.0 and 7.0, but that may vary depending on the variety. If your soil is too acidic (with a low pH), you must add limestone at the rate recommended by the test results. Overly alkaline soil requires the addition of sulfur. Further improve the soil by working in a 2- to 4-inch layer of compost into the top 6 inches of the ground, and add any fertilizers at the rate recommended by the soil test results.
A power tiller breaks up the top 12 to 18 inches of soil so it has a loose texture, while also working amendments into the soil. You can also break up the soil and work in amendments with a shovel, which is best suited for converting a small lawn area to a bed. Dig down 8- to 12-inches and break up any soil clods as you dig. Once dug and amended, you can arrange your plants in the bed. Place larger plants near the center or rear of the bed, then surround them with lower-growing varieties. Space the plants as specified on their labels so they don't become overcrowded as they reach their mature size.