Plastic Mulching: All You Need to Know

A homesteader’s life, despite what any person who lives the 9 to 5 thinks, is not a simple one. Countless tasks are constantly being added to the work schedule, therefore it is vital to be organized and willing to embrace technology, tools or techniques that help to render this lifestyle achievable.

The usefulness of plastic for mulching is one such technique could be useful for you to consider in your own garden, regardless of its size.

vegetables grown on plastic mulch

Popular since the nineteen fifties plastic has been a mulching material used by commercial growers, and has found a strong following among the home growing and the Homesteading community.

The popularity enjoyed by plastic in the growing community owes its success due to the profound effect that it has on the quality and measure of crops that are grown and its unique ability to extend the growing season.

Being able to grow a larger quantity of superior quality crops for a professional grower means increased revenue and profit, for the Homesteader a healthier supply of food.

There are clear benefits in using plastic materials to help grow produce. Let’s investigate how this product works.

The Battle for Effective Weed Control

Weeds are not always the best friend of any gardener no matter the size of the garden. Any area of exposed soil, whether in a cultivated area or not, can be completely overrun by weeds in a matter of days.

This invasion, although not a problem in unproductive areas is a major problem in any area that is used to grow flowers, vegetables or any other crop. Weeds will create a poor growing environment since they consume valuable nutrients and compete for root space.

The simple truth is that a poor growing environment will result in any crops being of poorer quality and reduced quantity.

It is possible to keep weeds at bay by hand, or by using any of the various commercial or homemade weed killing products, but this is a time-consuming, never-ending battle, especially if the cultivation area is large.

One of the utmost effective tools in the fight against the demon weeds is the employment of plastic mulch.

Annuals have a lifespan of one season and propagate by spreading their seed once they have grown to maturity. The plant dies, however, the seeds will germinate and grow new plants that will repeat the cycle indefinitely, unless they are killed before they grow to the stage where they will sow their seeds.

Perennials are different because the root structure of the plant remains alive, whilst the above-ground part of the plant will die off, they will, however certainly grow back the following year from the roots left in the soil.

Pulling up or cutting off the foliage section of a perennial weed is effective as it clears the garden of weeds, but they will, without a doubt grow back again, resulting in further pulling or cutting in a never-ending cycle.

The only surefire ways to remove the majority of weeds for as long as possible is to:

  • Interrupt annuals seeding cycle
  • Destroy the roots of perennials

The usage of plastic as a mulch offers the ability to influence and control environmental factors that has a direct influence on how plants grow.

Nearly all climatic areas experience a sudden growth of weeds before spring arrives. This is an ideal time to clear large areas of weeds by covering the area with sheets of black plastic. This a suitable technique to utilize when preparing an overgrown area that has not been cultivated before.

As the sun is unable to reach the soil, masses of seeds are prevented from germinating. Those that are able to germinate are not able to grow fully since in the absence of sun photosynthesis cannot function. It is the process of photosynthesis that allows a plant to produce food that is vital for its growth and development.

The plastic will also prevent any rain from entering the soil, consequently preventing seeds from germinating. With the lack of sun, water and the increased temperature that will be experienced by the soil a lot of the perennial roots will also be destroyed.

It is later possible to remove the plastic to plant crops in the soil. As the majority of the weeds are killed, you can plant in this area without disturbing the soil excessively.

Although this sounds, and indeed is, a simple solution to the weed problem, it is, however, important to remember that it is not a complete solution, there is no one-stop solution to removing weeds completely, and they will grow again.

Not all of the perennial roots will perish and only a small section is required to let new growth develop, some seed will be in the lower levels of the soil and can be bought to the surface in the preparation process where they can germinate.

The seed will also find their way from other areas as they are broadcast by wind and animals such as birds.

For flower gardens, it is possible to lay plastic sheets between any flowers on any bare soil to reduce the growth of weeds in these areas.

One solution to improve the aesthetics is to cover the plastic sheeting with another mulching material that will be much more pleasing to look at.

Bark and gravels are both popular products to achieve a more pleasing appearance. The bark will, however, need replacing periodically and the gravel does lose its luster after some time.

For gardens that have graveled areas as a design feature or as a path, plastic sheeting under the gravel does help to prevent weeds growing through.

Some weeds can still grow in the gravel as we have seen wind and animals will move them about to different areas of the garden. However, the weeds will have small immature roots and can easily be removed by hand.

Depending on the orientation and size of the graveled areas it may be necessary to create small holes in the plastic to allow rain to drain through, and to prevent pools of water from being created.

For areas where veggies or other crops are grown, plastic mulching can be used in different ways to help reduce the proliferation of weeds.

Generally crops are grown in rows leaving areas of bare soil between the rows which normally will not be used for cultivation but as a walkway to gain access to the crops. Although crops are not going to be grown in these areas weeds will be happy to occupy this space.

A strip of plastic on the walkway will help to restrict the growth of weeds therefore only the areas being cultivated will allow weeds to grow. Weeds can be cleared from this area by hand or a tool.

The plastic can be secured in this place to create a long-term protective barrier that still allows cropping and harvesting in the growing area for a number of seasons.

An alternative option is to cover certain areas in the cropping area with plastic sheets that can have holes cut into to be able to insert plants into the soil below.

The size of the hole is important as it will affect the care of the plants, too small and it is difficult to apply any side dressing to the plants without damaging them, too large and weeds, although in reduced numbers, will easily be able to germinate, grow and consequently compete for nutrients in the soil.

Commercial growers operate machinery that is able to lay plastic, puncture holes, and insert plants and water all at the same time. Large areas can be planted very quickly using this technique, however, the average gardener or the Homesteader does not need this level of automation.

We have mentioned some of the environmental factors that are affected by the exploitation of plastic as a mulching material, we should now look at the specific factors in detail to understand clearer the processes that cause the plastic to function as an effective mulch.

Effective Soil Temperature Control

Obviously covering the soil with a sheet of plastic will affect the micro-climate above the soil that the plastic is covering.

One of the major factors that plastic alters is the soil temperature. The plastic affects the temperature by altering the relationship between the rate of absorption and reflectivity. The corresponding energy differences within this relationship affect the temperature of the soil.

The color of the plastic largely determines its energy-radiating behavior and its influence on the effect on the microclimate, as does its thermal contact resistance due to its proximity to the soil.

For maximum effectiveness, it is important that the plastic is in close contact with the soil, and for it to be fixed securely positioned. On hot sunny days, the dark mulch surface temperature can surpass 130°F / 54°C. This could create injury or damage to nearly all plant parts that are in direct contact with the mulch.

Crop injury can also happen regardless of whether the harvest is in direct contact with the hot plastic mulch. During the day, it is possible for a tunnel to build up between the plastic and the soil. Hot plastic that is allowed to flutter can cause damage to stems, especially with young tender plants.

Dark plastic mulch is commonly used in growing vegetables because it is a hazy blackbody safeguard and radiator.

Dark mulch assimilates maximum UV, and infrared frequencies that are being transmitted by the sun, it subsequently re-transmits this energy as warm radiation or long-frequency infrared radiation back into the air.

While the conductivity of the dirt is high, compared to that of air, a significant part of the vitality consumed by dark plastic can be moved to the dirt by conduction.

Soil temperatures under dark plastic mulch during the daytime in average climatic conditions are commonly 3° F higher at a 4-inch depth compared to uncovered soil.

Conversely, clear plastic mulch retains minimal sun based radiation yet transmits 85% to 95%, with relative transmission relying upon the thickness and level of the haziness of the polyethene. In this way, daytime soil temperatures under clear plastic mulch are able to be increased as the radiation is able to act upon the soil.

Temperatures are commonly 8° F higher at a 4-inch depth compared to those of uncovered soil.

We have so far concentrated on the effects of plastic heating the soil to aid crop production, and whilst this is the case for the climate in the majority of geographical areas, there are some areas where the climatic conditions produce excessive heat to the soil.

In these locations, a plastic made of a black layer topped with a white layer is useful in decreasing soil temperatures. The dual layers help to reflect a large amount of the solar radiation, and shade the soil.

Clear plastic mulches by and large are utilized in the cooler locales in the United States, such as, the New England states.

Despite the temperature effect on the soil, clear plastic is not as efficient in controlling weeds as is black, since it permits the sun through allowing photosynthesis to work.

It is also important to remember that not all crops will benefit from the increase in soil temperature that is provided by plastic mulch. There are loads of cool-season crops such as peas and lettuce that will not benefit from the increased temperatures.

Does the Color of the Plastic Matter?

We have seen how the difference in the color of the plastic mulch controls the variables in different ways. In warmer climatic areas black plastic can increase the temperature to a level that is far too high for various plants. The solution to this problem for those who still want the other benefits of plastic mulching is to employ white plastic.

Although black or clear plastic are clearly the most popular options, different colors are being investigated to find, which have different optical characteristics that will reflect different radiation patterns into the canopy of plants, thereby affecting the growth and development of plants.

There are some signs that red mulch may have some positive effects on certain plants. Increase in yields has been observed with some melon and zucchini.

Evidence of elevated biomass accumulation and often yield with certain strains of tomato providing the rows are planted in a North-south direction. Although the effects are quite small for large-scale cultivation the use of red plastic mulch may be worthwhile.

Pepper plants grown on either green or silver plastic mulch showed evidence of benefit by producing larger fruit compared to other colors.

Muskmelons grown on blue, red, silver, and green mulch to produce a higher crop yield than plants grown on others colors. In addition, the fruit was larger from plants grown on brown mulch compared to those grow on black mulch.

Despite these effects being measurable it is not at this stage understood what causes the difference in plant growth.

Research is now in progress in trying to understand if this effect is due to the different light wavelengths reflecting on the plants influencing photosynthesis, seed germination, or if the different colors create the effect by subtle changes in the microclimate under the plastic.

Another style of mulch being tested includes the photo selective or wave-length-selective mulches, which transmit radiation in certain selective regions of the electromagnetic spectrum whilst not effecting the photosynthetic wavelength.

Since they absorb photo synthetically active radiation and transmit solar infrared radiation, they offer a compromise between clear and black mulches. These mulches offer the weed control properties of black mulch but are intermediate between clear and black mulch in terms of the effect in soil temperatures.

These mulches can be blue-green and are able to warm the soil similar to clear mulch but have a similar weed control effect as black mulch.

Highly reflective silver mulches are also being produced that will allow soil temperatures to be controlled whilst repelling aphids.

Clearly, as the world climate is changing at a rapid rate the manipulation of microclimate with the use of various types, and colors of plastic mulch may prove vital in maintaining acceptable food supply levels in the future.

Soil Moisture Retention Benefits

As plastic mulch helps to cut the amount of water that can evaporate from the soil, higher moisture levels are easier to maintain. Evaporation is reduced by as much as 70%, consequently the amount of extra water required by the crops is greatly reduced. For those paying for water, this will help to cut water consumption and indeed water bills.

Effective moisture control is vital since over-watering plants is very easy, and is one of the most common causes of poor plant growth and death. Plants that are over watered will not grow soundly and will drown.

Constant damp conditions can also create fungal disease problems that will have a severely negative effect on plants.

A simple solution to this problem is to install a soaker hose or a drip irrigation system onto the cultivation area before any plastic is placed. With an irrigation system in place, it is possible to accurately control how much water is being applied and where the water is going.

The irrigation system also has the advantage of making it easy to efficiently administer any liquid feed to the plants.

Higher soil temperatures can result in high levels of water evaporation that can result in water condensation on the under surface of the plastic, and the surface level of the soil becoming dry. When this occurs, it can result in uneven temperatures and moisture levels, something that plants do not appreciate.

Precautions should be taken to ensure that this does not happen. One such precaution is to use plastic that has been manufactured with anti-condensation properties.

Reduce Leaching of Fertilizer and Nutrients

Anything that grows requires the correct balance of certain nutrients to enable growth that realizes their full potential.

High levels of water from natural sources or from irrigation can dissolve and wash the nutrients out of the soil. Fertilizers added in the soil to enhance growth can also be washed away by excessive water.

The controlled environment established by the use of plastic mulching enables a reduction in the amount of extra water required by the plants, therefore reducing the quantity of nutrients that are washed away and helping to create an improved growing environment.

The plastic also offers a degree of protection from heavy rain that can devastate cultivated areas.

Extended Growth Cycle

One major benefit of using plastic mulching in certain climatic areas is that it is possible to start the growing cycle earlier in the year. The plastic mulching acts much like a greenhouse since it allows climatic variables to be altered to help and stimulate plant growth.

Uniformly raising the soil temperature early in the season brings the planting season forward. Equally, there is a benefit of extending the growing as the opportunity to support soil temperatures at the end of the growing season is also possible.

The benefit of raising the soil temperature is that crops will be ready for harvest between 7 and 20 days earlier than normal climatic conditions would permit

This is particularly useful in encouraging fruit-bearing trees to break out from their winter cycle. Extending the growing season for some crops will create the possibility of multiple harvests.

Higher Crop Quality

Since the plastic also acts as a physical barrier between crops and the soil, it creates a far cleaner growing environment. Crops that are in contact with the soil can be damaged and become useless.

The barrier can inhibit the growth and spread of certain disease and rot. Numerous fruit and foliage diseases overwinter in the soil waiting for the next season’s growth to materialize before emerging to cause havoc.

Combining reduced disease with improved retention of nutrients due to improved weed control and reduced leaching encourages healthier growth of produce.

Healthier and larger crops with less waste equate to improved financial returns for the homesteader or commercial grower a superior food supply.

Reduction in Soil Compaction

Bare soil creates a crust when exposed to the sun and rain. The crust and the need for weed control requires extensive cultivation to keep the soil in a condition that it is an efficient growing medium.
Since the plastic reduces weed growth and protects the soil from the elements it remains loose and thoroughly aerated, and able to support oxygen levels that aid microbial activity.

Reducing Erosion

In areas that experience high rainfall, exposed soil is susceptible to being eroded. Erosion not only damages the physical situation of the soil, it can destroy crops and have a harmful effect on its nutrients.

Carefully positioned plastic mulching helps to reduce erosion problems and can also prevent animals from interfering with the soil and eroding it in their own inimitable way.

For areas that experience regular flooding raised beds covered in plastic mulch also helps to protect crops and the physical structure of the soil helping to reduce damage.

Reduce Root Damage

Since the plastic improves the soil condition by reducing compaction and minimizing weed growth the amount of cultivation that is required is minimized.

While some plants have a small root structure others are quite extensive reduced cultivation causes less root damage. An undamaged root structure is efficient and reduces the stress on the plant, consequently, the plant is capable of growing stronger and healthier.

Plastic for Effective Mulching

When plastic was initially used there were very few styles available, however the development of plastic manufacturing techniques means that a wider range of plastics is now available.

The original form of plastic, although very efficient as inorganic mulch, was not very environment friendly, and since a large quantity of plastic was used a large amount of plastic waste that is very slow to deteriorate has developed. Recycling is an option for most plastics, but not all can be bothered without any financial gain.

Since much of this largely intact waste has found its way into the soil, it has, in some areas, had an adverse effect on the soil by interfering with the natural flow of water and nutrients. In some areas, this has affected the salt content of the topsoil, and subsequently reduced the crop growing ability.

With the introduction of biodegradable films, it became possible to till the material into the ground for it to degrade. Some biodegradable plastics have been impregnated with nutrients in an attempt to treat the plastic as a soil feed when tilled into the ground.

At this time little is known about the long-term effects on the soil or the environment by introducing large quantities of this product into the ecosystem.

Plastic mulches are available in a range of thicknesses from 0.6 to 2.0 mils (0.0152 to 0.0508 mm). A 1 mil gauge thickness is generally appropriate for the majority of vegetables.

Mulches are normally produced as a smooth plastic or with a grid structure incorporated into the surface. The grid structure provides an element of strength in the plastic and prevents it from moving around too much.

Is the Use of Plastic Cost-Effective?

Large quantities of high-quality crops are easily achieved by using plastic mulch, but what of the cost? The use of plastic mulch for the commercial grower is an expensive option, the plastic introduces extra cost factors with labor and specialized equipment that is required to install and replace it.

Can this, therefore be a financially viable option for the homesteader? Most homesteaders don’t use equipment or paid help to install plastic mulch, thus greatly reducing costs.

As is the case with lots of things, balancing the cost and time involved in using a product needs to be compared to the extra produce or quality that is achieved by using that particular product.

For homesteaders, the use of plastic mulch as a tool to control the microclimate can be cost-effective in saving the time required in controlling weed infestation and the increased levels of quality crops over an extended time frame.

The cost of using plastic as mulch can also be reduced to lower levels by ensuring that it is used for as many seasons as possible. Since homesteaders are mostly experts at repurposing materials, it is likely that the plastic will be useful for several tasks. Multi-use of materials is an important factor in maximizing the return on any product.

Environmental Protection is Vital

Recent years have seen a growing awareness regarding the damage that plastic has inflicted on the delicate balance of the world Ecco System

The proliferation of discarded plastic has been declared a pollution crisis that requires immediate action. Thousands of animal species have been affected by eating plastic, or being trapped in it. The convenience and the relatively low cost of plastic have created the single-use throwaway culture.

Plastic is produced from petroleum-based materials, and often contain additives that formulate them into a stronger and durable material useful for millions of applications. Unfortunately, the additives help to create a product that will take four hundred years to break down.

However, plastic is a generic term, and is also used as a description for numerous products that have been developed that are not as dangerous as original plastic.

Original plastic was a cumbersome product to use for mulching since, as it wasn’t biodegradable, it required removal from cultivated areas. It was bulky requiring extra machinery and labor, and difficult to dispose of, since landfill sites imposed handling charges.

Biodegradable plastic mulch has been in development for some time. Early versions were photo degradable, they decomposed in the presence of light. These did not prove popular with growers as they did not decompose in a uniform rate leaving fragments in the soil. These fragments could prove harmful to future crops.

Biodegradable plastic, incorporating plant starch has also been developed. Since starch is biodegradable, this plastic will disintegrate into small particles faster than traditional plastic.

Soil microbes break this material down into water and carbon dioxide. They offer similar properties to that of traditional black plastic in terms of soil warming and its ability to give effective weed control.

As should be expected these products are extra costly, however, the reduction of removal and disposal costs still create an attractive product.

Summary

It is clear that plastic mulch has been an essential tool for the commercial and the Homestead grower for several years. With historic and present-day development of the plastic, it strived to keep its importance and relevance, as its effect on the ecosystem has been better understood.

We have seen how, by controlling the microclimate, the mulch maintains a growing medium that is of beneficial structure, nutrient-rich, with a balanced moisture content that is protected from weeds. The control and protection give a near-perfect growing environment that enables high crop yields.

Where I live, plastic mulch is used extensively in large plastic greenhouses. This combination offers a high level of control over the microclimate inside, so, a year-round growing cycle is possible and high levels of high-quality crops are achieved.

As important as plastic mulch is to produce large quantities of high-quality crops, it’s also disappointing to see that agricultural plastic, especially since it has become a biodegradable product, is now seen as a product that can be discarded by the side of the road.

We have seen how destructive older types of plastic can be on the environment and animal life, however that should however not detract from the significant benefits that it has made to cultivation in the past and will continue to into the future as technology and science continue to enhance mulching materials in additional positive ways without the negative effects on our delicate biosphere.

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