Plastic mulch seems like a dream come true if you struggle with maintaining a productive, weed-free garden. You can roll it out, secure it in place, and your weed problems practically disappear!
This agricultural film lays over the soil surface to suppress weeds, conserve moisture, and warm the soil temperature, among other benefits. But like any synthetic garden material, you should carefully weigh its pros and cons before layering it over your soil.
While it is very popular amongst many gardeners, landscapers, and farmers, this thin film also has significant drawbacks regarding its environmental impact. Microplastics, chemical leaching, and harm to soil microorganisms are significant concerns. Here, we examine the pros and cons of using plastic mulch in your garden.
What is it?
This synthetic film blocks weeds, retains moisture, and warms the soil for early planting and improved crop conditions.
Plastic mulch is a thin synthetic film laid over garden soil to create a protective barrier that prevents weeds, holds in moisture, and increases the soil temperature. It allows you to plant earlier in the season and moderate environmental conditions without installing a greenhouse.
For crops like strawberries or lettuce, it keeps the harvestable portions cleaner and prevents soil splashback. For tomatoes, red plastic can boost early ripening and increase yields. The material is widely used on commercial farms but has recently become more popular amongst gardeners and landscapers.
Most films are made of one to two mil polyethylene (LDPE), which is among the safest types of plastics and least likely to leach chemicals into the soil. However, the film can still release microplastics and degrade in the UV rays over time. The synthetic mulch is applied from a roll and secured by burying its edges with soil or anchoring with staples.
It comes in many colors, but black and dark green are the most common because they absorb sunlight and warm the soil beneath them. White and light-colored films create the opposite effect by cooling the bed temperature by up to 20°F, which is very helpful when growing in extra hot climates.
Benefits
From reducing weeds to earlier harvests, it clearly offers many benefits to the modern gardener. Despite its synthetic (non-biodegradable) composition, it is eco-friendly in some regards.
Those serious about growing their own food may want to take advantage of the methods used on high-production commercial farms. However, the hobby gardener may find that the environmental drawbacks outweigh the benefits. Either way, here are notable ways it can make gardening easier, based on science and our personal experiences.
Weed Suppression
This weed-suppressing method blocks sunlight, preventing weed growth.
Nobody likes weeding! Any weed-suppressing method that can save your back is worth considering. The number one benefit is its ability to prevent weeds from germinating and growing.
When an opaque film is laid over the soil, it instantly stops sunlight from reaching any plants except your crops (which poke through holes). Any weeds germinating beneath the plastic are smothered and killed by lack of sunlight. This results in less weed competition for your plants, yielding healthier crops and higher yields. Aside from the occasional weed that pops up close to the crop hole, you won’t have to hoe or hand-pull as often.
This is particularly helpful for crops that stay in the ground for long periods, like berries, tomatoes, leeks, and some herbaceous perennials.
Clear Weeds Before Placing
You cannot just throw plastic mulch over a weedy bed and smother weeds right away. You have to clear the bed and create a clean soil surface before applying the film. A hand hoe is usually sufficient, but you can also do shallow tillage (with a tiller), use a lawnmower, or try occultation, which involves laying a thicker tarp over the soil for a week or two to kill any growing weeds.
No matter what method you choose, be sure you have removed any existing weeds before laying the plastic film on top of it. If you attempt to mulch an already weedy bed, the weeds will poke through the plastic and cause it to rip prematurely.
Alternative: This is an inorganic mulch, which means it won’t biodegrade or nurture the soil in any way. If you want to reap similar weed-suppressing benefits while building your soil organic matter, choose an organic mulch instead.
Shredded leaves, straw, bark, or wood chips are great options for different garden areas. They similarly suppress weed growth by preventing sunlight from reaching the weed seeds below. As an added benefit, they provide food for microorganisms to slowly break down, adding more nutrients and minerals (rather than microplastics) to your soil over time.
Increased Yields
Extensive agricultural research at universities confirms plastic mulch significantly boosted yields and fruit quality.
Extensive agricultural university research proves that this product dramatically increases yields. Strawberries, tomatoes, corn, zucchini, melons, sweet potatoes, basil, and peppers are the most studied crops, and all show significantly higher yields and fruit quality when grown in black or clear plastic films. As sunlight hits the mulch and reflects thermal radiation up, the overall increase in temperature and light reflection makes these warm-weather crops extra happy.
Water conservation beneath the mulch also reduces water stress, improving the fruit’s quality. For example, in tomatoes, studies show this mulch promotes more flower clusters, earlier flowering, and less disease. It even helped reduce blossom end rot due to more consistent water availability beneath the plastic.
Soil Temperature
Plastic films, depending on their color, can either warm or cool the soil significantly.
Warming
Plastic films can warm the soil by as much as 20°F or cool the soil temperature by -10°F, depending on the color and conditions. This means you can plant earlier or later in the season without worrying about temperature damage to your crops. As the sun’s UV rays hit a dark-colored plastic film, heat is radiated through the soil profile, creating a warmer root zone for your crops to germinate and develop.
Cooling
Conversely, reflective or light-colored plastics can decrease the soil temperature by reflecting solar radiation and keeping crops cooler in southern climates. Black plastic absorbs the most UV for soil warming, while clear and silver mulch reflect the most UV for soil cooling.
Soil temperature is often more important than ambient temperature because the soil takes longer to warm than the air. Dark mulch essentially makes summer come faster by creating a reservoir of warmth in your garden beds. This is especially helpful for heat-loving plants prone to transplant shock, like melons, squash, and cucumbers. When the roots of young plants move from a seedling cell to pre-warmed ground, they instantly feel cozy and at home.
Alternative: Instead of using plastic to warm your in-ground beds, you can set up metal raised beds as a long-term solution. The soil in a raised bed naturally warms more quickly in the spring due to the sun’s rays hitting the sides of the planting container. This alternative reduces your plastic use and creates an aesthetically pleasing bed that still allows for early planting.
Row cover is another soil-warming option that adds 6-10°F of frost protection. When draped directly over your young crops, it creates a microclimate of warmth right by the soil surface. Although row cover is still a synthetic plastic material (usually made of woven polypropylene), it lasts longer and, with proper storage, can be used for several seasons. It also keeps pests off your crop leaves, a task mulch cannot compete with.
If cooling is an issue, straw mulch is your best alternative. Straw mulch creates a fluffy barrier over the soil that keeps crops cooler in the summer. Research shows that straw mulch can moderate soil temperature to prevent overheating in crops like lettuce or brassicas that prefer cooler temperatures. This is awesome news for southern growers! However, beware that straw mulch can keep your soil colder and wetter in the spring if you mulch too early. It’s best to apply once the temperatures have sufficiently warmed and you become more concerned with overheating.
Season Extension
This mulch extends growing seasons for both northern and southern growers, benefiting a wide range of crops.
All this talk about soil warming and cooling may have you wondering whether this product can extend your growing season. The answer is yes! With this tool, northern growers can plant earlier in the spring and grow later in the fall. Southern growers can keep conditions cooler in the summer and extend their season for heat-sensitive crops.
Synthetic mulch is a cheaper and easier solution if you can’t afford a greenhouse, shade cloth, or low tunnel infrastructure. A longer growing season means extended harvests of your favorite warm-weather crops like tomatoes, peppers, melons, corn, basil, and other frost-sensitive vegetables. It also means less heat stress and pest pressure for cool-weather crops like broccoli, cauliflower, lettuce, or cilantro.
Moreover, plastic films allow you to expand the growing zones of subtropical perennials like citrus trees, succulents, or even pineapples. Studies show that polyethylene and polypropylene mulches have significant benefits in perennial fruit production but still need to be removed and replaced often due to plastic degradation.
Conserve Moisture
This mulch prevents soil evaporation and conserves moisture, reducing the need for frequent watering.
Evaporation is the main enemy of thirsty garden crops. When the sun hits bare soil, it sucks up the moisture from the upper layers and dries it out very quickly. Again, plastic film can come to the rescue by holding moisture in.
You don’t have to worry about your soil drying out if you have soaker hoses or drip irrigation lines running beneath the plastic. You can water much less and ensure your crops never experience drought stress.
But as you’ll read below, this water conservation benefit has a major drawback: the plastic is not breathable. Nobody can breathe with a plastic bag over their head. Similarly, the soil cannot breathe and exchange oxygen with the environment when it is covered in this film. The major moisture-holding benefit can bite back with soggy or oversaturated soils.
Alternative: If your soil tends to dry out very quickly, adding compost and an organic mulch like shredded leaves can provide the exact same benefits without the plastic waste. Keep your soil consistently moist and well-drained by nurturing it with rich decomposing matter and a 1-3” thick layer of leaf mold.
Soils with higher percentages of organic matter are proven to retain more moisture and drain more quickly after heavy rains. Research shows that every 1% increase in soil organic matter helps hold 20,000 more gallons of water per acre! This water-holding capacity can make a huge difference even in a small-scale garden, particularly in drought-prone areas!
Cleaner Fruits
Mulch prevents fruits from touching the soil, reducing rot, mold, and slug damage.
If you’re tired of fruits rotting in the soil, plastic can keep them off the ground. This means cleaner harvests with less washing. Low-growing fruits like strawberries especially benefit from fruits resting on plastic, resulting in less mold formation and reduced instances of slug damage. If you don’t have the infrastructure to trellis upwards, vine crops like melons and cucumbers also benefit from laying on a clean surface rather than directly on the soil.
As we’ll explore below, you may find some concerns with your food sitting on plastic for extended periods. While some film mulches are food-safe, the potential chemicals in others are unlabeled or unclear.
Alternative: Once again, an organic mulch like dry leaves or straw can serve the same function without the plastic usage. It keeps the fruit clean but may still provide a harbor for pests. Trellising, hanging baskets, or vertical container growing like a Greenstalk Planter are other great options for cleaner harvests.
Prevent Erosion
Prevent soil erosion in your garden by using mulch to keep soil in place and protect plants from wind and rain.
Erosion is what happens when wind and rain blow or wash away your soil. This is a major problem for soil degradation worldwide, but it is just as important in your backyard garden.
After investing so much time and energy into your soil, you want to keep it in place as much as possible. A plastic film holds the soil where it is and protects it from the harsh effects of the elements.
Different Colors for Different Purposes
Red mulch promotes early ripening and potentially reduces pests.
Recent innovations in the world of plastic mulch have made this tool extra versatile. Researchers have found that certain colors of mulch help achieve different results in unique conditions. This gives you more flexibility for different climates, crops, seasons, and locations in the garden.
Black is the industry standard because its opaque UV-absorbing color creates the most thermal radiation, increasing the soil temperature and warming plant roots. It is perfect for northern growers who need to moderate their soil warmth through cold nights and unpredictable springs. Beware that black mulch could cause excessive heat stress in hot climates.
Green is most commonly used on vining crops like cantaloupe, watermelons, cucumbers, and summer squash. The green film converts solar heat and transmits infrared radiation, making the air directly above the soil surface warmer. At the same time, it blocks photosynthetic active radiation (PAR), meaning it excels at suppressing weeds. The result is earlier harvests, higher yields, and less weed competition.
White-on-black or silver-reflecting mulch decreases the soil temperature to help keep crops cooler. They reflect the sun’s rays away, ensuring the soil doesn’t overheat in peak summer. The opacity of the mulch determines how much light can get through, meaning this mulch is less effective at suppressing weeds compared to dark-colored films. Highly reflective silver mulch can also help repel aphids and delay virus symptoms in fall squash.
The most exciting innovation is red film. The red color reflects infrared light up into the plant canopy, leading to earlier and more even ripening of tomatoes, peppers, and melons. Some evidence shows that red mulch can also reduce pest pressure like aphids and root-feeding nematodes.
Reduced Agrichemical Use
Plastic film application eliminates the need for herbicides, making organic gardening easier.
Gardeners who have previously relied on herbicides to deal with aggressive weeds can stop spraying after they apply this film. Most of us aim for organic growing, but perhaps your landscapers still spray perennial thistles and bindweeds because they feel they have no other option. When you apply plastic film, the need for herbicides is eliminated.
Drawbacks
In spite of all its incredible benefits, plastic films have just as many drawbacks. After all, most available materials are not biodegradable, and we’ve all heard about plastic’s ability to persist in the environment for hundreds of years. Before you cover your garden in film, consider these ecological and functional issues.
Microplastic Contamination
The main drawback is microplastic pollution, which is harmful to the environment.
The biggest issue with plastic mulch is microplastics. Anyone who has worked with this film knows firsthand how easily it can rip. Once it rips, there is no going back. Thousands of tiny pieces of plastic may reside in your soil for the rest of eternity (and those are just the pieces you can see with your naked eye!) You cannot pick it all up.
Even before cleanup time, solar radiation, aging, and weathering of the film cause it to rip into smaller pieces throughout the season. Rather than breaking down into biodegradable chunks, plastic gradually deteriorates into smaller pieces that never decompose.
Research shows that the use of plastic films has significantly contributed to microplastic pollution in soils around the world. Full recovery of the plastic film is virtually impossible because the fragments spread so deep and far. The microplastic pieces can also interact with pathogens, heavy metals, and other pollutants, leading to greater environmental toxicity.
To make matters worse, microplastics wind up in the insides of worms, birds, rodents, and other creatures all the way up the food chain. If you are already astonished by the amount of plastic pollution in our oceans and forests, you may want to second guess before putting any more into your garden. Just one season of plastic film use may leave microplastics in your garden soil for centuries to come.
Inorganic Mulch
Plastic does not break down like organic mulch, lacks soil-nurturing properties, and can harm the soil ecosystem over time.
Unlike organic mulch, inorganic plastic films never break down. They do not nurture the soil like straw, leaves, bark, woodchips, or other natural mulches do. There is no nutrient or microbial benefit to using these mulches. In fact, their synthetic composition makes them problematic because microorganisms cannot decompose the material. Organic mulches offer many more benefits to the soil ecosystem and improve the soil over time, while this artificial mulch can actually degrade it.
Excessive Moisture and Surface Water Runoff
This mulch can lead to water accumulation, soggy soil, and fungal issues due to lack of drainage.
Because plastic prevents water from evaporating, moisture can accumulate in the soil and cause soggy or waterlogged conditions. Synthetic films are extra risky for plants prone to root rot because they create an environment for disease-causing fungi to breed and proliferate.
Additionally, the plastic film has no holes to allow water penetration. If it rains really hard, the accumulation of water on top of the film can cause compaction or runoff. Surface water runoff can lead to puddles and stagnant pools of water on top of the bed or in the pathways.
Chemical Leaching
This product can potentially contain harmful chemicals like phthalates, posing health risks to humans and plants.
While most plastic mulches are made of low-density polyethylene (LDPE), a fairly safe type of plastic, the risk of chemical leaching is not to be ignored. No plastic can be made without chemicals, and many of them (like BPA and phthalates) can have alarming health impacts on humans and plants.
Greenhouse films are sometimes manufactured in food-safe settings. However, the production of plastic sheet mulches is largely unregulated. We don’t know exactly what is inside the plastic unless the manufacturers tell us.
Studies show that polyethylene films can contain phthalates. Other plasticizers that may leach into soil include benzylbutyl phthalate and acetyl tributyl citrate. It is unclear how or if these chemicals transfer into the soil and crops, but the potential risk should not be underestimated.
Accumulation of these plasticizers in our soils, crops, water, and bodies could have long-term impacts that we aren’t yet aware of. If you wish to avoid even unknown risk factors, you may want to opt out of using sheet mulches or at least try to source a BPA-free and phthalate-free product whenever possible. If you are chemically sensitive, avoid it altogether.
Harm to Soil Microorganisms
It can harm soil microbes, impacting their lifecycles and disrupting soil texture.
Soil microbes are the hardest workers in our gardens. They make the soil hospitable to plants by breaking down organic materials, improving soil structure, and transforming nutrients into plant-available forms. Unfortunately, plastic mulch could harm this complex underground ecology.
Data shows that microplastics are proven to harm soil microbes by changing soil texture and disrupting their lifecycles. If plasticizers and chemicals pose a risk to animals as large as humans, they likely also impact the microscopic beneficial bacteria and fungi trying to aid our crops.
These microorganisms improve yields, bolster plant health, prevent disease, and create more nutrient-dense food. If you want to maintain a thriving soil microbiome, don’t use plastic films.
Lack of Airflow to Root Zone
Consider alternatives like landscape fabric or row covers for better soil aeration with warmth.
The absence of permeable holes poses a problem for roots. Just like humans, plants and soil need to breathe. That is impossible to do with a plastic seal over your head. The lack of airflow through a plastic film into the soil can cause disease and soil health issues.
This drawback has not been studied extensively, but it is worth remembering that plastic has zero breathability. Consider landscape fabric or row cover if you want to warm your crops while allowing airflow through the soil.
Single-Use Disposability
Environmentally conscious gardeners should explore longer-lasting or biodegradable alternatives.
In most cases, you cannot reuse plastic mulch. It lasts for one season or less. If you leave it in the ground for too long, the material degrades, creating more microplastic problems. There is little room for recycling or repurposing this tool.
Disposable, single-use plastics are a major source of pollution and “forever plastics” that ultimately end up in landfills. Anyone concerned about the environment or waste reduction should consider longer-lasting or biodegradable alternatives.
Environmental Pollution
This type of mulch poses environmental concerns, generating microplastics and air pollution when burned.
We’ve discussed the health and safety implications of plastic mulch, but the long-term environmental impact is also worth mentioning.
This mulch creates harmful microplastics that take centuries to break down and can also pollute the air if burned. There is no real “sustainable” way to eliminate it because it ultimately ends up somewhere, contributing to the colossal plastic pollution problem we already have on Earth.
Typically, this type of plastic cannot be recycled, adding to the issue; it will end up in a landfill with no potential for cycling it through again.
Aesthetics
It detracts from the natural beauty of your garden, making it look artificial and unattractive.
Last but not least, it’s downright ugly. You likely started gardening with the vision of a backyard oasis of vegetables, herbs, fruit trees, and beautiful flowers. Plastic dampens this appearance by adding an artificial layer over the ecosystem’s natural beauty.
Sure, it can suppress weeds, making your garden look cleaner, but it certainly won’t look natural. Unfortunately, you can’t really cover up the plastic mulch with bark or wood chips, as this can cause more degradation issues and reduce the effectiveness of the plastic mulch overall.
Final Thoughts
Plastic mulch can be beneficial, but the risks and pollution warrant alternative solutions. Ultimately, this product may have a place in commercial agriculture because it helps protect farmer’s livelihoods, reduces weeds (and herbicides), and improves yields. But in the home garden, it may not be worth the risk. We won’t judge you if you need to use plastic film on an extra weedy bed, but we highly recommend exploring alternatives like raised beds, tarping, row covers, and organic mulches.
Still, if extra early high-yielding tomatoes are important to you, there’s no shame in giving it a go! Just be aware of potential consequences, like little pieces of plastic floating around in your garden soil. The choice is yours!
