Sustainable Hemp Farming: Are U.S. Growers Doing It All Wrong?

How hemp farming could hurt the planet


The hemp industry is set for significant growth thanks to the passing of the Farm Bill into law in December 2018. The legislation ensures that it is now federally legal to grow industrial hemp in the United States. With no legal ramifications, we may now see a golden age of hemp growing – around 80 years too late!

In the 1930s, hemp was set to become a billion-dollar crop until the Marihuana Tax Act of 1937 destroyed the industry. According to Successful Farming magazine, America is likely to see 100,000 to 200,000 acres of hemp production in 2019; although seed supply will limit production.

Hemp is grown very differently depending on what it is being used for. Farmers growing hemp for CBD will have a maximum of 1,600 plants per acre. Hemp grown for bioplastics and textiles has up to 400,000 plants per acre! Hemp for mass-market products grows tall, and farmers harvest the tops for seeds and use the stalk for various industrial uses.

Experts believe that up to one million acres will be used for hemp within five years. Sales of hemp reached more than $1 billion in 2018, and that was before it became fully legal to grow! American farmers are turning to hemp as a money crop because a decent yield of food-grade hemp can yield up to $750 per acre. Compare that to soybeans, which offer a $150 profit per acre.

The ongoing trade war with China is hurting American farmers; another reason why so many are flocking to the new hemp industry. When grown responsibly, hemp is a sustainable crop. However, the continuing use of plastic mulch is in danger of transforming a ‘green’ industry into yet another example of one that hurts the environment.

What is Plastic Mulch?

what is plastic mulch

Mulching is an effective method of protecting and insulating a plant’s delicate root systems against inclement weather conditions. It improves the nutrient profile of the soil, helps it retain more moisture, and reduces erosion. Growers have the option of using organic and inorganic mulch.

Organic mulch is great for the environment and is created from biodegradable materials, including dried leaves, straw, wood chips, and grass clippings. Inorganic mulch involves the use of materials such as crushed gravel, stone, and river rock.

However, there is also plastic mulching which has become extremely popular in hemp farming, even though it is terrible news for the environment. It is classified as an ‘inorganic’ mulch and involves the use of polyethylene to shield plants from the weather. This form of mulching gained popularity in the 1950s and was widely used in commercial vegetable and berry production.

Typically, the polyethylene film is a thin black plastic sheet that works to reduce moisture evaporation, prevent soil erosion, and insulate the soil. There is also a clear polyethylene sheet used in plastic mulching. The dark sheet is preferred for warming up the soil, preventing weed growth, and retaining the soil’s moisture.

The clear film is used for promoting faster growth in early spring and also does an excellent job of warming up the soil. However, the black sheet is preferred because it is better for stopping weed growth. Proponents of plastic mulch point out its benefits, which include the following.

Better Soil Structure

As a gardener, it is frustrating when your soil compacts and becomes a mess. Plastic mulching traps moisture and heat, an action which prevents the loss of nutrients. Also, you can see the black sheeting, which ensures no one walks into the garden.

Soil Insulation

As you’re probably aware, certain plants, such as vegetables, don’t handle the cold of winter too well. The same can be said for hemp. The polyethylene film helps retain heat. Farmers find that plastic mulch heats the soil by around five degrees Fahrenheit.

Weed Control

Weeds are bad news for any garden, but plastic mulch effectively suppresses weed growth in a large space. If you install polyethylene sheets in your hemp garden, you will prevent weeds from getting the sunlight needed for photosynthesis, so they die.

Faster Growth & Better Crop Quality

Hemp is a seasonal crop when grown outdoors, but if you use plastic mulching, you can grow your plants earlier in the season. As it warms up the soil, it enables you to plant your hemp crop up to three weeks ahead of its usual schedule. Those who use plastic mulch also say it provides better quality crops by preventing the growth of diseases and rot.

Reduces Root Damage Risk

When you use polyethylene sheets, you don’t need to disturb your garden, barring incursions between the plastic rows. When plants can grow in undisturbed soil, the plant roots can grow and spread into the ground deeply. Cultivation causes root damage, but most gardeners have no choice as they want to deal with weeds. If you have a weed-free garden, you can leave your plants in peace and reduce the risk of root damage.

Several studies have looked at the effect of plastic mulch on agriculture in China. A study by Gao et al., published in Science of The Total Environment in February 2019, discovered that plastic mulching increased crop yield in China by 24%. The sheeting also boosted water use efficiency by 27%.

A study by Liu et al., published in Environmental Research Letters in September 2014, found that plastic mulching increased grain yields by 20-35% and cash crop yields by 20-60%. By 2011, China used 1.25 million tons of plastic film, which covered around 20 million hectares of land.

Unfortunately, these increased yields come at a high cost to the environment. In both studies, the researchers pointed out the need to improve plastic film standards to control pollution. They also said that large amounts of the residual plastic film have detrimental effects on water, nutrient transport, and soil structure.

The plastic revolution has taken hold in the United States as well. The use of plastic mulching is so popular that it is called ‘plasticulture.’ Back in 2015, the Modern Farmer journal lamented the growth of an industry that was already worth $5 billion. The publication suggested it would be worth double that by 2020.

Why Plastic Mulch is Slowly Ruining the Environment

Large scale hemp farmers are following the lead of others in the agriculture industry by using plastic mulch instead of its biodegradable equivalent. Hemp is supposed to be a sustainable crop, but by using a tool that’s an environmental hazard, we’re repeating the same old mistakes that have led to the mess we’re now in. Around 99% of respected scientists believe that climate change is real, and we’re doing nothing to turn it around; it may be too late already.

Climate change has a myriad of potential effects, including heavy rainfall and arid soil. Higher atmospheric temperatures lead to more arid soil with our plant life in danger of suffering severe water stress. Hot air holds more vapor, so moisture that should be stored in the soil is instead hanging over our collective polluting heads. The result is torrential rainfall that damages crops and leads to erosion.

Plasticulture is championed as a solution to water shortages, and also the problem of feeding our expanding population. Alas, plasticulture causes immense pollution. It is believed that there are 55,000 tons of used agricultural plastic sitting in Florida’s dumpsites and landfills. There are dumpsites so large that you can see them from the Kennedy Space Center!

Plastic mulch is also expensive, and at the end of each growing season, the mulch is pulled up and taken to a dumpsite. The plastic is taken to South America and burned. To make matters worse, the plastic is a valuable resource because it is congealed natural gas with an energy density greater than gasoline! The energy content of a pound of plastic mulch film is higher than a pound of coal.

The issue of whether plastic mulch is bad for the environment has been discussed for decades. In 2003, the United States Department of Agriculture looked at the material to decide if it was harmful or helpful. It wrote that plastic mulch increases surface runoff from rainfall and irrigation. Bear in mind that large scale hemp growers possibly apply pesticide (growers of other crops certainly do) which runs off into nearby water supplies.

Overall, there are numerous downsides to using plastic mulch.

An Environmental Disaster Zone

Removing the film from fields requires specialized equipment, and disposing of the plastic is difficult. Landfills tend to ask for more money to deal with plastic disposals, which end up being shipped overseas anyway.

It isn’t biodegradable like organic mulch because it doesn’t break down completely. In the study by Liu et al., the authors wrote about how plastic film mulch was mainly composed of polyvinyl chloride, which doesn’t degrade in soil. While the film doesn’t degrade much, it could still result in the formation of harmful chemical products, including phthalate, ketones, and aldehydes.

Worryingly, the study claimed that large amounts of the residual film could result in unsustainable farmland and damage the agricultural environment. In China, excess levels of residual plastic film in the soil reduced cotton production by 15%.

Excessive Moisture

While plastic mulch traps moisture well and ensures water doesn’t evaporate, too much moisture can be a bad thing as it makes it easier to overwater and drown the crops. Damp growing conditions may increase the risk of disease and infestation, which causes farmers to use pesticides!

Excessive Heat

While hemp is fairly durable, the same can’t be said for all crops. ‘Cool-season’ crops such as peas and lettuce could die from overheated soil.

Increased Salt Content in the Soil

In China, mulching for between 5 and 20 consecutive years resulted in a 122% to 146% increase in the topsoil’s salt content.

Final Thoughts on Plastic Mulch in Hemp Farming

While plastic mulching has a slew of benefits such as increasing yield and allowing farmers to start growing earlier in the season, it causes a huge amount of damage to the environment. In what is another case of profit before people, large scale agriculture uses plastic mulch to increase its profit.

Shockingly, hemp farmers are guilty of the same sin. Hemp is a sustainable crop that can do wonders for our environment. Sadly, the profit motive means it is going down the oft-trodden route of damaging the world we live in.

Hemp farmers must hold themselves to a higher standard and use biodegradable mulch instead. There are plenty of materials you can use, including:

  • Garden Compost: It helps prevent weeds from growing, provides extra insulation to help during cold spells, and ensures your hemp plants can access nutrients immediately.
  • Bark & Wood Chippings: This option looks aesthetically pleasing while surrounding your garden borders. Composted bark is a favorite of gardeners because it has a more natural look than bark chips.
  • Leaf Mold/Mushroom Compost: These options aren’t used that often but help provide your borders with lots of nutrients and also ensure much-needed insulation during winter.
  • Straw: The straw’s scratchy surface keeps slugs at bay and is popular amongst strawberry growers because it also keeps the fruit away from the mud after heavy rainfall. You can use straw on top of another mulch to ensure moisture stays locked in.

The best time to apply the mulch is during the middle of spring until the beginning of the fall season because the soil is warm. Non-biodegradable mulch options such as gravel, slate, and crushed seashells don’t offer much nutritional value, but they help conserve moisture and also make your garden look gorgeous!

Alas, we don’t expect large scale hemp farming operations to use biodegradable mulch. Why would they, when plastic mulch film is widely available, helps them grow more hemp in a shorter time frame, and boosts their profit margins? Unfortunately, the practice of using plastic film for mulching is here to stay, and each use places another dagger in the heart of the environment. It would be a terrible shame if hemp became implicated in this crime.