Rototilling is a common method for preparing garden beds, using a machine with rotating blades to churn the soil. Many people assume this mechanical action will kill an existing lawn, but the reality is often the opposite. For turf removal, tilling generally does not destroy the grass and frequently aggravates the problem by ensuring the turf quickly returns, sometimes thicker than before. This counterproductive result stems from the grass’s unique biology and the damage tilling inflicts on the soil’s structure.
The Direct Answer: How Tilling Affects Grass
Tilling works by chopping the grass plants and their root systems into smaller fragments and burying them within the top layer of soil. This process initially appears successful because the visible green blades are destroyed and mixed into the dirt. However, the root crowns and pieces of underground stems are not killed; they are merely severed and dispersed.
The effectiveness of tilling depends heavily on the type of grass being removed. Bunch grasses, which grow in clumps and lack spreading runners, might be temporarily suppressed by this fragmentation. Running grasses, such as Bermuda grass or quackgrass, are difficult to eliminate because their root systems are designed for rapid lateral spread.
These fragmented root pieces retain enough stored energy and viable growth points to sprout new shoots. The tiller effectively replants these pieces, distributing the grass across a much wider area. Unless the tilled area is immediately subjected to intense drought or heat, the turf will recover and emerge as a dense carpet of new growth.
The Mechanism of Grass and Weed Propagation
The primary reason tilling fails as a turf removal method lies in the biology of certain grasses, which propagate through specialized structures called rhizomes and stolons. Stolons are modified stems that creep along the soil surface, rooting at the nodes to form new plants. Rhizomes are similar structures, but they grow horizontally underground, allowing the plant to spread beneath the soil line.
When a rototiller passes through turf, its spinning blades act like a mechanical pruning tool, chopping these runners into numerous small segments. Each segment of a rhizome or stolon, even a small one, contains a node capable of generating a completely new, independent plant.
The tilling process effectively multiplies the problem, turning one large root mass into hundreds of potential new plants scattered throughout the tilled area. Instead of killing the grass, the tiller has accomplished the plant’s goal of vegetative reproduction and ensured its rapid re-establishment.
Soil Health Consequences of Tilling
Beyond turf regrowth, mechanical tilling degrades the physical and biological health of the soil. The churning action breaks apart soil aggregates, which are stable clumps of soil particles bound together by organic matter and microbial secretions. Destroying these aggregates weakens the soil structure, making it more vulnerable to compaction and erosion.
Repeated tilling can lead to the formation of a dense, impermeable layer just below the tilled depth, known as a tillage pan or hardpan. This layer restricts the movement of water and air, impeding root growth and reducing the soil’s ability to absorb rainfall. The mechanical disturbance also introduces a rush of oxygen deep into the soil, which causes a rapid oxidation and loss of organic matter and carbon to the atmosphere.
This disturbance harms the soil food web, which includes beneficial fungi and bacteria essential for nutrient cycling and plant health. Tilling severs the extensive network of mycorrhizal fungi that help plants absorb nutrients and water. By damaging this microbial community, tilling reduces the long-term fertility and resilience of the soil.
Effective Methods for Turf Removal
To successfully remove turf without the negative effects of tilling, methods that smother or cook the grass over time are more effective. One reliable, chemical-free technique is sheet mulching, also known as lasagna gardening. This involves mowing the grass very low, covering the area with a light-blocking layer of overlapping cardboard or newspaper, and then topping it with organic material like compost or wood chips.
The cardboard layer prevents photosynthesis, starving the grass of light, and the organic material retains moisture to encourage decomposition. Depending on the climate and the thickness of the material, this method takes about six to eight weeks for the turf to die and begin breaking down.
Another effective option, particularly in hot climates, is solarization. This involves cutting the grass short, watering the area thoroughly, and then covering it tightly with clear plastic sheeting. The plastic traps solar radiation, heating the top six inches of soil to high temperatures, which kills the grass, its roots, and many weed seeds. This process requires four to eight weeks during the hottest part of the year.