Spring has arrived, which often prompts calls and emails to the Illinois Extension office about starting a new garden or installing a landscape bed. These are typically going in where there is currently lawn. So, the common question becomes, “What’s the best way to kill the grass before planting vege-tables or flowers?”
Most homeowners don’t have access to a tiller or prefer to avoid herbicides. And that’s OK because there is more than one way to kill a lawn. The next alternative is smothering or covering the lawn so it blocks sunlight and cannot photosynthesize. There are several methods to eliminate turfgrass for future planting beds.
Rake or mow fallen leaves into the area to establish a native plant bed 6-12 inches deep. Allow leaves to remain until spring, and then remove them and spread out again until you have a layer 2-4 inches deep. The leaves become a mulch layer and plants can be planted directly into the soil.
Trees grow well in Illinois, and there are often sources of woodchips in communities as arborists and other tree care professionals perform routine maintenance or tree removal. Sometimes woodchips are even free.
Apply woodchips 4-6 inches deep. This will smother most weeds. Tenacious perennials can grow through the mulch but can be easily pulled. When ready to plant, reduce the mulch depth to 2-4 inches deep.
Arborist woodchips are coarser and allow better water and air exchange to the soil. Shredded wood mulch typically knits together, forming a “shell” over time. Shredded wood mulch will need to be cultivated periodically to prevent a shell from developing.
The black plastic material prevents light from reaching the soil surface. This kills the living plants under it and inhibits seed germination. Gardeners can scalp the vegetation with a mower, then lay down the plastic.
If you have access to a tiller, till and rake out a prepared soil surface and then cover. Tilling creates an opportunity for seed germination. Covering after tilling kills germinating seeds, creating a stale seedbed. Remove plastic before planting.
If smothering is the only goal, cardboard is another possible material. Remove any tape, labels, staples or other packing material. Remove cardboard before planting. Cardboard can become hydrophilic and hold excess water in the soil, making it a poor option to remain as a mulch.
Large rolls of biodegradable paper designed for garden use can be found at many garden centers. Newspaper works in the same way, but typically must be covered by mulch to hold it in place. If using newspaper avoid glossy paper.
A thick layer of straw can help suppress existing plant growth. Once the grass is dead, transplants can be directly planted into the soil.
Smothering your lawn to install a garden or landscape bed does take a bit of planning so enough time passes to kill the grass underneath. It may take up to two weeks to eliminate the lawn. Once the lawn is dead, a consistent layer of mulch 4 inches deep is a great way to prevent future weeds from sprouting in your new planting bed.