Clear existing vegetation from garden sites using one of several methods.The process you choose depends on how much time you have, how much effort you want to invest, and the kind of vegetation you're removing.
If you're dealing with turf or a groundcover, physical removal will work effectively. For a planting bed laced with pernicious weeds, such as quackgrass, dandelions, mugwort, or wiregrass, you'll need an aggressive stance to eradicate them.
Whichever method you use, define the bed edge before beginning. Use a sharp spade to slice into vegetation. With the blade inserted into the soil, rock the spade back and forth to form an accessible trench. If you use an herbicide to remove vegetation, create a physical barrier or shield using cardboard, plastic, or lumber to prevent any spray from drifting onto surrounding plants.
Pictured: Use a supple garden hose to define a bed outline. View the bed from interior rooms and outdoor living areas. When you're satisfied with the shape, outline the edge with flour and start digging.
Method 1: Physically Remove Vegetation
Removing plants by hand involves intensive labor but offers a low-cost approach to clearing a bed. When digging vegetation by hand, budget roughly an hour to hand-clear 100 square feet, although that estimate varies based on the type of vegetation you're removing. Sod comes up easily, as do some groundcovers. If you face deep-rooted perennial weeds, you'll dig deeper, which will slow your overall progress.
When clearing vegetation by hand, remove as little soil as possible; the top few inches of soil is the most fertile. As you start removing the first chunks of existing vegetation, examine the soil beneath. You shouldn't see any grass rhizomes, plant roots, or rooted stems. If you do, dig a little deeper and remove more soil.
When working with a groundcover that roots along stems, search around in the proposed garden site and locate crowns of the plant. Focus on digging those out; the remaining stems should pull up easily.
Method 2: Use an Herbicide
An herbicide eradicates weeds and turf in short order, killing the aboveground portion of plants, roots, or both. It's an excellent choice when time is short. Read the package label; typically you can plant in an herbicide-treated area within 10–14 days. One of the most commonly used herbicides for killing grass and weeds is glyphosate.
If you aspire to an organic garden, you might not want to use herbicides. Many professionals in the prairie restoration movement, which generally embraces organic principles, use an herbicide such as glyphosate, which becomes inactive in soil after a few days, to prepare planting areas and wipe out existing nonnative plants.
An excellent use for herbicides is on a slope. Spray plant tops with herbicide, and roots will remain to hold soil in place. When greenery dies down, you can dig through the remaining roots to plant. Within two years, you won't see any sign of the previous vegetation.
If you need to wipe out weedy roots, spray plants in late fall, when carbohydrates are moving from leaves into roots. At this time, herbicides move more readily into roots, and you should be free of problem weeds come spring.
Slower methods to clear vegetation get beds ready in four weeks to six months.
Method 1: Smothering
Smothering works by depriving plants of sunlight. Typically, a smothered bed is ready for planting in six to 12 months. Spread layers of material over existing plants, starting with a layer -- cardboard, 10 layered sheets of newspaper, or dark plastic -- that allows no sunlight to penetrate. Use mulch, such as compost, grass clippings, straw, or chopped leaves, for the second layer. Many gardeners start a layered bed in fall; the bed is ready in spring.
"Lasagna gardening" works well when you know you'll be constructing a new bed in a certain place. Start with a light, impervious layer and add layers as they're available. At any point during the process, if the layers are deep enough or the soil beneath is diggable, you can bury kitchen waste in the same area to attract and feed beneficial soil organisms.
Method 2: Solarization
Solarization is an excellent choice for a heavily weed-infested site. With solarization, you harness the sun's energy to bake the soil above 140°F to kill weed seeds, insect eggs, disease spores, and nematodes. Cut down weeds and till up roots with a heavy-duty tiller. Rake weeds and stems, and rake a second time to even out the soil. Water the area thoroughly to soak the top 4–6 inches of soil. Cover the soil with a sheet of clear construction-grade plastic (1–6 mil), stretching it tightly. Seal any seams with clear tape to trap heat generated beneath the plastic. Use heavy blocks or bricks to hold down the edges until you can bury them to anchor the plastic and retain heat. In four to six weeks, the soil will be sufficiently heated and you can plant.
Note: In the Northern Hemisphere, the best time to solarize the soil is when the sun is at its highest point in the sky: June and July. This method works best in a garden site that receives at least six hours of direct sun daily.
Mix in Amendments
When you have removed existing vegetation, it's time to work amendments into the soil. This task is the most labor-intensive aspect of planting a garden. The goal in working the soil is to improve drainage on lower levels, if needed, and to work organic matter into the upper 6–8 inches of soil.
As you blend in amendments, try to create gradual changes in the soil from top to bottom. Work in amendments from the top down, aiming to increase organic matter in the topmost layer, where the majority of soil organisms and plant feeder roots are. Lower soil layers might need only to be broken up to enhance drainage. Before digging, make sure soil isn't overly wet or dry.
Mix in amendments by hand, using a digging fork or round-point spade. Hand-digging makes sense in a small garden or to save money. Going over the ground two or three times with a spade will effectively blend amendments into the soil. For a large garden, rent or borrow a rototiller. A tiller isn't effective in rocky soil or a bed filled with tree roots, but it works fast in sandy or loamy soil. In clay soils, don't churn the same area of soil too much to avoid compacting lower layers where digging tines strike.
In soil with many tree roots, a digging fork (also called a spading fork) maneuvers well without damaging roots. A digging fork also makes quick work of soil preparation in sandy soil.
To mix in amendments, add a 1- to 2-inch layer of organic matter on top of the soil and work it into the top 6–8 inches. If digging by hand, use a digging fork to turn forkfuls of soil on its side, mixing in the amendments as you turn the soil. Repeat, adding another 1 inch of organic matter plus any other amendments. Dig these amendments in 3–4 inches deep. This amending method yields a gradual decrease in organic matter from the soil surface to deeper layers.