Why Should You Mulch? (5 Benefits Explained)

Mulch functions

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If you are looking for a solution to all the problems in gardening, it would most likely be mulching. 

Mulching retains moisture, prevents erosion, prevents weeds, maintains soil temperature, prevents diseases, and even increases crop yield and immunity.

In this article, we will show you how mulching can achieve these magical functions in your garden.

1. Retain moisture

The most well-known function of mulching is its ability to retain water by shading the soil and reducing the amount of evaporation on hot and windy days.

The best results come with a thickness of 2 inches (5 cm), saving up to 40% of water while a thickness of 4 inches (10 cm) can retain up to 50% of water (McMillen, 2013).  Increasing the thickness even more up to 6 inches (15 cm) would retain the same amount of water in the soil as a 4-inch mulch.   

Plastic mulch can conserve more water because they are completely impervious and prevents water from evaporating.

Mulching also ensures a more even distribution of moisture throughout the soil.  But, plastic mulches might not be ideal for small gardens because the plastic also prevents water from getting into the soil, preventing rain and other conventional forms of watering from reaching the plants. The only way to water plants with plastic mulching is to use a drip irrigation system.

The best types of organic mulch are straw, leaves, and wood chips, or inorganic mulches like gravel, limestone, and crushed concrete.

Living mulches or cover crops produce mixed results for water retention and conservation. On one hand, the crops can prevent evaporation from the soil, and increase water infiltration into the soil. But on the other hand, they also absorb water from the soil, which is then lost in plant transpiration.

2. Prevent erosion

Mulching is an effective way of preventing soil erosion as it covers the soil surface, protecting it from the direct impact of wind and rain.

Bare or exposed soils can be easily blown away by wind or washed off by rainwater. The risk is even more on sloped soils since the inclination increases the speed of the running water.

Organic mulches can greatly reduce runoff velocity due to the roughness of the material and can help water to infiltrate into the soil.

The amount of mulch used will determine how effective it will be at preventing erosion. According to a study, covering as little as 20% of the soil with mulch can reduce erosion by 40% (Babcock and McLaughlin, 2019).

Mulching that covers 80 to 85% of the soil can reduce erosion by 90%, preventing seeds and seedlings from getting washed off and creating a more optimal environment for germination.

3. Prevent weeds

Mulching can keep weeds down to a great extent by blocking their access to light. 

The most effective mulch type in suppressive weed growth is a plastic cover, which can suppress up to 95% of weeds, followed by paper (up to 89%) and rice straw (up to 75%). 

This is according to a three-year study that compared the effects of 5 mulch types in controlling the number of weeds (Anzalone et al., 2010). 

Mulch typeQuantity of weeds under control
Rice straw75%
Barley straw<55%
Maize harvest residue35%
Black plastic81-95%
Brown kraft paper65-89%
Source: Anzalone et al. (2010)

Rice straw was the most effective organic mulch type as it could control 75% of the weeds.  Not only can it block sunlight, rice straw is also believed to be “allelopathic” as it releases chemicals that can stop the germination of weed seeds.

All the mulch types investigated could control most weed species, except the purple nutsedge which was able to pierce through the plastic and could only be controlled by paper mulch.  

Growing living mulch, such as barley, clover, oats, and hairy vetch, can also suppress weed growth by blocking light from getting to the soil.

But the living mulch needs to be planted immediately after the area has been cleared and should be a fast-growing species, such as buckwheat, with high biomass. This is so that the plant can quickly outgrow and suppress the weeds.

It is best to use two or more cover crops together, like an annual (e.g. buckwheat, oats) with a perennial (e.g. alfalfa). This is to compensate for different growing periods so that there is an unbroken succession of living mulch all year round.

4. Maintain soil temperature

Mulching maintains soil temperature by insulating the soil from fluctuations in air temperature, keeping the soil warm in winter and cool in the summer.

Mulches can increase or decrease the soil temperature by about 2-3 °F (1-2°C). This change is greater within the top 2 inches (5cm), but can extend to about 5 inches (10cm) down into the soil.

Organic mulches can insulate the soil below from the seasonal changes in air temperatures because they prevent evaporation and the direct impact of solar radiation. On the other hand, plastic mulches tend to increase soil temperature, as the plastic absorbs heat from the sun and transfers it to the soil.

In a study, researchers found that mulching using grass reduced summer soil temperature on average by 2 °F (1.13 °C) while plastic mulches increased soil temperature by 2 °F (1.4 °C).

  Mulch typeSoil temperature in different months
JulyAugustSeptemberAverage temp
No mulch79.01°F (26.14°C)77.03°F (25.02°C)78.3°F (25.73°C)78.1°F (25.63°C)
Grass mulch76.7°F  (24.84°C)75.7°F (24.27°C)75.92°F (24.40°C)76.1°F (24.50°C)
Black plastic81.41°F (27.45°C)80.40°F (26.89°C)81.68°F (27.60°C)81.33°F (27.41°C)
White plastic83.52°F (28.62°C)78.67°F (25.93°C)79.92°F (26.62°C)80.71°F (27.06°C)
Source: Tegen et al. (2015)

The mulch also protects the soil from the cold air. During cold days organic and plastic mulched soils are warmer than bare soils. This is because the mulch traps the heat and prevents it from escaping into the atmosphere.

A study found that mulched soils were warmer than bare soils at night when air temperatures were down, but became cooler when the sun was up and air temperatures were higher (El-shaikh and Fouda, 2008).

5. Improve plant health and crop yield

Mulching can improve plant health by adding nutrients to the soil, and increasing microbial activity in the soil.

Organic mulches decompose over time, releasing simple sugars and nutrients into the soil. The soil microbial activity increases because they feed on sugar (link).

Microbes such as mycorrhizal fungi help increase plant uptake of water and plant minerals by seeking moisture and nutrients beyond the reach of plants via an extensive network of hyphae.

And because of the increased access to water and nutrients in the soil, plant health and yield improve.

Mulching also can increase crop yield by suppressing weeds, preventing diseases, retaining moisture, and maintaining temperature.

Here is a table showing the increases in yield due to mulching.

  CropYield (tons per hectare)  Yield increase (%)
UnmulchedMulched
Tomato6.028.2727.20
Chickpea5.917.3219.26
Cotton1.672.2224.77
Mustard0.410.6132.78
Rice5.396.8321.08
Lentil0.800.8910.11
Maize2.494.7647.68
Wheat7.247.797.06
Mung beans1.021.3625.00
Soybean1.321.5715.92
French beans12.7314.109.71
Potato24.0030.0020.00
Barley3.774.2711.70
Source: Iqbal et al (2020)

6. Prevent diseases

Mulching can also improve plant health by providing optimal conditions for microbes that can fight off pathogens and diseases.

Microbes such as the Trichoderma fungi (link) and the Bacillus bacteria (link) serve as a natural fungicide that can prevent bacteria and other pathogens in the soil, greatly reducing the chance of fungal plant diseases such as root rot.

Studies have proven that putting mulch on the understory of wine grapes could reduce fungal infection by 97%.  The reason is believed to be an increased quantity of beneficial microbes due to an increased quantity of vine debris for decomposition.

A layer of mulch also creates a barrier over the soil and helps prevent fruit rot, a condition that can occur when fruit and vegetables fall to the ground. It prevents mud and any pathogens from being splashed onto flowers and leaves during rain or overhead watering.

Final words

Mulch is really the magic solution to most problems in gardening, from retaining moisture to reducing weeds, moderating soil temperature, improving plant health, and reducing damage to the plant.

Happy gardening!

References

Anzalone, A., Cirujeda, A., Aibar, J., Pardo, G. & Zaragoza, C. (2010).  Effect of Biodegradable Mulch Materials on Weed Control in Processing Tomatoes. Weed Technology, vol 24 (3), pp. 369-377.

Babcock, D., & McLaughlin, R. (2019, May 20). Mulch Options for Erosion Control on Construction Sites. NC State Extension Publications.

Gholami, L., Banasik, K., & Dharvishan, A. K. (2014, October). Effectiveness of Straw Mulch on Infiltration, Splash Erosion, Runoff and Sediment in Laboratory Conditions. Research Gate.

University of Nebraska-Lincoln. (2015). Long-term UNL Study Examines Impacts of Cover Crops on Soil, Water. CropWatch – University of Nebraska-Lincoln.

Freehan, K. & University of Nebraska-Lincoln. (n.d.). Mulch to Conserve Soil Moisture | Nebraska Drought Resources. University of Nebraska-Lincoln Extension.

Dong, W., Si, P., Liu, E., & Yang, C. (2017, December). Influence of film mulching on soil microbial community in a rainfed region of northeastern China. Research Gate.

Vila, M., Beaury, E. M., Blumenthal, D. M., Early, R., & Ibañez, I. (2021, March 1). Understanding the combined impacts of weeds and climate change on crops. Iop Science.

Creech, E. & United States Department of Agriculture. (2018, July 24). Discover the Cover: Managing Cover Crops to Suppress Weeds and Save Money on Herbicides. Farmers.Gov.

Currell, C. & Michigan State University. (2015, April 1). Controlling soil erosion with cover crops. Michigan State University Extension.

DeDecker, J. & Michigan State University. (2013, December 4). Cover crops Part 2: Valuable cultural component of your organic weed management toolkit. Michigan State University Extension.

Hoorman, J., & Sundermeier, A. (2017, May). Using Cover Crops to Improve Soil and Water Quality. Ohio State University.

El-Shaikh, A., & Fouda, T. (2008, January). Effect of different mulching types on soil temperature and cucumber production under libyan conditions. Research Gate.

Stelli, S., Hoy, L., Hendrick, R., & Taylor, M. (2018). Effects of different mulch types on soil moisture content in potted shrubs. Water SA, 44(3 July).

Tegen, H., Mohammed, W., & Dessalegn, Y. (2015). Effects of Mulching Materials on Soil Temperature under Polyhouse Condition. International Institute for Science, Technology, and Education.

Bell, T., Borrelli, K., Isbell, S., Fleishman, S., Kaminsky, L., & Cloutier, M. (2021, April 22). Understanding and Managing Soil Microbes. Penn State Extension.

McMillen, M. (2013). The Effect of Mulch Type and Thickness on the Soil Surface Evaporation Rate. [email protected]

Shanks, L., Moore, D. E., & Sanders, C. E. (n.d.). Soil Erosion. University of California, Davis.

Iqbal, R., Razar, M. S., & Nazar, M. (2020, May 18). Potential agricultural and environmental benefits of mulches—a review – Bulletin of the National Research Centre. SpringerOpen.

Carol loves to garden and research to help others grow their green thumb.

She is working towards her dream of living close to nature.

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