The Role of Organic Mulching in Sustainable Weed Control

Organic mulching in containers | Debalina Saha, MSU Horticulture

Weed management is an essential but challenging process as part of greenhouse propagation. The presence of weeds can rob crops of vital resources needed for growth, in addition to becoming a vector for diseases and pests. The most common method of dealing with weeds is that of chemical herbicides, but several factors related to greenhouse production, such as enclosed spaces and climate control, can lead to the vaporization of herbicides, thereby putting crops at great risk of damage and death. 

As a response to this issue, Assistant Professor Debalina Saha and Graduate Research Assistant Supti Saha Mou of the Michigan State University (MSU) Department of Horticulture have explored the safety and effectiveness of non-chemical weed control methods, primarily that of organic mulching, in a recent e-Gro alert. 

Organic Mulching Explained 

According to the pair, “Organic mulch is the application of naturally derived materials on the surface of the soil with the aim of protecting the soil from erosion, conserving moisture, enhancing fertility, controlling weeds, and regulating soil temperature.” Additionally, as a result of being naturally derived materials, they are biodegradable, allowing them to decompose over time and attribute to soil health. 

By covering the soil surface, organic mulch blocks the transmission of sunlight, thereby preventing the process of photosynthesis needed for weed seed germination. Additionally, the packing of organic mulch “acts as a physical barrier that prevents new weed seeds from reaching the soil and establishing themselves.” 

Lastly, organic mulch can modify the soil environment as a method of weed control. Organic mulching cools the overall temperature of the soil, which prevents some weed seeds that thrive on heat from properly germinating. Additionally, it limits oxygen availability to prevent weed growth. However, “this effect must be carefully managed, as excessive mulch thickness can also affect ornamental crop growth by reducing oxygen availability to the crop roots.” 

Types of Organic Mulches 

Some of the most common types of organic mulches include: 

• Grass clipping 
• Hardwood chips 
• Pine bark 
• Pine straw 
• Rice hull 
• Sawdust 
• Shredded cypress 

Pros of Organic Mulching 

Some of the advantages of organic mulching include: 

• Microbial activity: Mulch supports beneficial microbes for better overall soil health. 
• Moisture retention: Mulch traps moisture in the soil, which reduces water evaporation. 
• Soil enrichment: Mulch adds nutrients to the soil when it decomposes. 
• Temperature regulation: Mulch insulates the soil, protecting plant roots in extreme hot and cold temperatures. 
• Weed control: Mulch blocks sunlight, preventing weed germination. 

Cons of Organic Mulching 

Some of the disadvantages of organic mulching include: 

• Costs and labor: The application of organic mulch can be costly and labor-intensive, making it more suitable for small-scale farming. 
• Disease and pest risks: Organic mulches may attract pests and increase disease risks in certain crops. 
• Negative crop growth impact: Some organic mulches can lead to nutrient deficiencies due to a “high carbon-to-nitrogen ratio.” 
• Limiting oxygen: Organic mulching can effectively limit oxygen supply to weed seeds but can also restrict crop growth if not monitored and controlled effectively. 

For more information regarding organic mulching benefits and limitations, please read the full e-Gro (Electronic Grower Resources Online) alert “Organic Mulching: An Effective Non-Chemical Weed Strategy.” Additional and current e-Gro alert pieces from Volume 13 (2024) can be found online.