Occultation: 8 Ways to Use Tarp in the Garden

We don’t often think of tarps as essential in the tool shed, but they are among the cheapest, most versatile garden tools you can use. Whether you want to smother a huge area of weeds or quick start a new clover lawn alternative, a tarp is up for the job. 

When you lay down a tarp, it becomes a passive worker, no matter the season or weather. Instead of using heavy machinery to rip up the soil, the heavy-duty material naturally blocks out the light and kills the weeds or grass beneath it. It can also warm the soil faster in the spring, suppress plant diseases, and protect it from erosion through winter.

Let’s dig into eight easy ways you can use a tarp to improve your garden!

What is Occultation (Tarping)?

The word occultation is the fancy term for using a tarp to cover soil for an extended period in the garden. Tarping is popular in gardens and on small farms because it requires very little effort and can clear large areas without disturbing the fragile soil ecosystem. You simply lay the tarp over a garden bed or a patch of unwanted plants, then weigh down the edges with sandbags or rocks and let the tarp work its magic. When you lift it up in 2 to 4 weeks, the weeds or plant residues beneath should be dead, and you can prepare the area for planting.

Tarping is a passive way to smother weeds, clear a bed, suppress grass growth, warm the soil, reduce tillage, and protect garden beds from soil erosion. Tarps can be made of polyester, canvas, nylon, or polyethylene. Dark colors effectively block out sunlight and water to kill any weeds beneath them. They can also warm the soil to promote more microbial activity. 

8 Ways to Use a Tarp in Your Garden

A UV-treated polyethylene silage tarp is the most popular style of tarp to use in the garden because it is heavy-duty and lasts for many years. Silage tarps are also called bunker covers or agricultural tarps. They are puncture-resistant and designed to withstand the rough wear and tear of rocks, debris, and intense weather. Reused banner vinyl, camping tarps, waxed canvas, and recycled material tarps are also available.

Tarps come in sizes small enough for a single raised bed or large enough to cover thousands of square feet. Use a tape measure to determine the size of your desired beds or the area you need to cover. On a home scale, try starting with a 20’ x 10’ tarp that is manageable and easy to fold with one person. If a tarp is too large for another use, you can always double-fold it.

No matter what type or size of tarp you choose, be sure to use viable weights to hold down the edges. If the wind catches underneath a large tarp, it can be very hard to wrangle it back down. Smooth, moderately sized rocks are easy and free, but be sure they don’t have any jagged edges that might tear your tarp. Bricks also do the job. Sandbags are cheap to fill, easy to carry, and can be stacked on a pallet when not in use. However, they do rip over time, and the sand can fall out. I advise avoiding landscape staples or anything that might punch holes in the tarp, as this will dramatically reduce its lifespan.

Once you’ve considered your tarp options, here are eight versatile ways to use it in the garden!

Smother Weeds

Weed smothering is the most popular and useful way to put a tarp to work in your garden. Simply lay out the tarp over a weedy bed, weigh it down, and wait four or more weeks for it to work its magic.

How it Works

Tarps block out sunlight, which means the weeds below cannot photosynthesize. The sun’s heat on the tarp (black side up!) also “bakes” any weeds below. Research shows that soil temperatures need to reach at least 104°F (40°C) under the tarp to fully kill any dormant weed seeds.

When the tarp is lifted, the ground beneath is usually ready for planting. All you need to do is rake aside the dead weed foliage and add a layer of compost, and you have a no-till garden bed with rich soil that is ready to plant!

This method has surely been used for decades or more, but it was most recently popularized by organic farmer JM Fortier in his famous book The Market Gardener. The concept of occultation (tarping to smother weeds) allows you to kill weeds without disturbing the soil with a rototiller or other machinery. Occultation is passive, which means less tedious hand weeding later on! If tarps are viable for small-scale commercial vegetable farms, surely they are functional in your home garden.

For excessively weedy beds or aggressive perennial weeds, you can lift the tarp periodically (every one to two weeks) and water beneath it. Leave the tarp off for one to three days. This will stimulate the remaining roots to send up more sprouts. When you lay the tarp over them again, it re-smothers the foliage. This slowly exhausts the perennial root structures. You may have to repeat the process a few times to fully kill established colonies of aggressive thistles, bindweed, or quackgrass. 

Tarping vs. Tilling

Nonetheless, tarping requires way less effort than hand-weeding and far more eco-friendly than using herbicides! Better yet, the tarp prevents further weedy infestation. If you rototill or dig through a bed with lots of perennial weeds, you could end up inadvertently spreading the weeds further because every little piece of root can sprout into a new plant. This method ensures you get to the root of the problem without harming your soil. All you need is some patience! 

Warm the Soil

Studies show that tarps can increase soil temperature by 30 to 40°F (17 to 22°C). If certain areas of your garden take a long time to warm up in the spring, a tarp with the black side up can draw in more solar rays to warm the soil quickly. It can even help melt snow! This is especially useful when it seems like you’re right on the cusp of spring but still nervous about light frosts. 

About 4-6 weeks before planting a warm-weather crop like melons, peppers, tomatoes, or cucumbers, cover the garden bed with a tarp. The tarp will help trap more heat to thaw the soil below and warm the temperature so that seeds or transplants will be cozier and more successful.

Remember that it takes more sunlight and prolonged heat to warm up soil compared to air. In the springtime, the soil will warm up slower than the air. You could experience an unseasonably warm day, but the soil may still be cool. Tarping helps you get in the garden sooner by attracting more sun rays to the covered beds. It’s still very helpful to use a soil thermometer to get an accurate reading before direct seeding any crop that requires warmer soil temperatures to germinate.

In hot climates, switch to facing the white side of the tarp upward to reflect sunlight and reduce heat buildup. You don’t want to bake your soil in peak summer!

Kill Grass to Prepare a New Garden Bed

One of the most eco-friendly suburban landscape trends is switching from a high-maintenance grass lawn to a front yard garden or clover lawn alternative. A tarp makes this process much easier and less destructive, but you will have to tolerate a plastic-covered yard for a few weeks to reap the most benefits. 

Tarps can easily smother a lawn as effectively as they smother weeds. No herbicides or rototilling needed! Lay out the tarp and cover all sides to prevent wind or water from getting underneath. If using multiple tarps, overlap them at least 6” so no grass creeps up between them.

Leave the tarp for at least three weeks to fully kill established turfgrass. Optionally, lift it once and water beneath it, then cover again for another 1-2 weeks. If you want to direct seed a new lawn like clover or creeping thyme, it is very important to thoroughly smother the grass below and exhaust the turf root systems. This will prevent aggressive grasses from growing back and outcompeting your new ground cover.

If you are establishing garden beds using the “lasagna garden” layering method, 2-3 weeks of tarping will usually suffice. Once you remove the tarp, immediately mound up your new beds with layers of compost or potting soil. Mulch the pathways with leaves or wood chips. This will complete the lawn-smothering efforts and make your yard look more beautiful right away! 

Flipping Beds

Imagine you have a messy bed full of exhausted spring lettuce with lots of weeds. You’re ready to plant tomatoes in its place, but you’re not quite sure how to prepare the bed. Wouldn’t it be nice to get rid of the lettuce without disturbing the soil beneath or doing a bunch of labor? Toss a tarp over the bed, leave it for 1-2 weeks, and you’ll have a clean slate to transplant your tomatoes! 

The tarp creates a dark, moist environment to kill off the previous crop and encourage microorganisms to break down any residues. When you pull the tarp off, you should have nice soil enriched with a fine layer of decomposed leaves from the previous crop. You can rake this aside or leave it in place to act as mulched organic matter. This process eliminates the need for tilling, hoeing, or yanking up old plants. The old roots can stay in place to nourish the microbial soil food web, which helps improve your soil and plant health over time. 

In the farm world, we call this “bed flipping” because you are essentially making one crop flip over into the next. Efficiently flipping beds allows you to grow several rounds of food in one season. 

If you are learning about succession planting (the art of timing multiple sowings of a crop for a continuous supply throughout the year), you will definitely want to try out the tarp method to speed up your successions and get the most out of your garden. Anyone interested in no-dig or no-till gardening should consider bed flipping with a tarp.

Space-Holder Between Plantings

Sometimes life happens, and you don’t have time to sow a cover crop or mulch garden beds in between plantings. A tarp can serve as a place-holder between plantings to keep the soil covered when nothing is growing in a bed. Whether it’s peak summer or the middle of winter, taking 5 minutes to secure a tarp over your garden beds can make a huge difference for the following crop.

If you’ve been learning about healthy garden soil, you know how important it is to keep your soil covered and protected as much as possible. Bare soil is vulnerable to erosion (blowing or washing away), weed infestations, and compaction. Nature doesn’t like to garden naked, and you shouldn’t leave your most valuable garden resource (the soil!) exposed to the elements without any plant roots or mulch to protect it. 

While organic mulch like leaves or compost, is better for nurturing soil over time, a tarp can serve as a temporary covering solution. It is a quick way to protect parts of your garden that aren’t currently in use. Whenever you find the time to replant that area, you won’t have to deal with a big, weedy mess because the tarp prevents weed seeds from germinating. 

In areas with heavy rain or snowpack, the tarp can also prevent the soil from compacting downward. Although some compaction is inevitable (most garden beds need an extra 1-2 inches of compost on top every year), the tarp ensures that large amounts of soil won’t wash or blow away.

Reduce Tillage

Tarps can help you reduce soil disturbance in the garden to protect the beneficial organisms that live belowground. Tillage is the mechanical disruption of soil with rototillers, plows, and cultivators. Every time you till, you destroy the fragile soil ecosystem by grinding the particles and structure into uniform sizes.

Tillage and the Belowground City

It’s helpful to imagine healthy soil ecology as a thriving city belowground. There is a huge diversity of populations that live in this city, including billions of bacteria, fungi, protozoa, nematodes, worms, spiders, and larger animals like voles or groundhogs. Each organism has a particular home in the soil structure. 

For example, mycorrhizal fungi form web-like networks between plant roots that are called mycelium. These beneficial fungi funnel water and vital nutrients through their networks to feed plants and boost their immunity against disease-causing organisms.

Anaerobic (oxygen-consuming) bacteria live in the open pore spaces between different particles, using the available water and oxygen to fuel their growth. While we often think of bacteria as negative, there are actually relatively few disease-causing bacteria in the soil. The vast majority of bacterial populations are beneficial, aiding in the decomposition of organic matter and mineralization of plant nutrients like nitrogen.

Once all these different organisms build homes in the soil, they boost the overall structure to help hold onto moisture during drought and quickly drain water after heavy storms. The belowground “city” uses infrastructure like particles and aggregates of different sizes to allow oxygen, water, and nutrients to flow freely, making it easier for plant roots to develop and thrive.

Any time you till, it effectively destroys this thriving ecosystem. All the different particles are ground to dust, and there is nowhere for the beneficial microbes to live. This leads to big problems like compaction, where the soil becomes hard like concrete, and plant roots have a difficult time breaking through. Tilling clay soil can be especially problematic because it often leads to reduced oxygen and soggy, waterlogged conditions that cause plant roots to rot.

Using Tarps to Reduce Tillage

It makes logical sense to reduce or avoid tillage as much as possible in order to protect your fragile soil ecosystem. But you still need to prepare beds, get rid of old crop residues, and eliminate weeds. As you read above, tarping allows you to do all of these steps in one. By replacing your tiller with a tarp, you can build stronger soil over time and boost the soil food web so your garden gets healthier every year.

Suppress Plant Diseases (Solarization)

Perhaps the most well-known use of garden plastic (beyond greenhouses) is solarization. Solarization involves using a plastic tarp to magnify the sun’s rays directly onto the soil surface to drastically raise the soil temperature so it kills off any pathogenic bacteria or fungi that cause crop diseases.

Any organic gardener who struggles with plant diseases like root rot, damping off (Pythium), Verticillium wilt, or soil-borne blights will be glad to know that you don’t have to use copper fungicides or strong chemicals to get rid of plant diseases! 

Solarization generally takes longer than weed smothering by tarp. If weeds are present, of course, they will die off as the soil heats up under the tarp. You need to leave the tarp over the bed for six to eight weeks in peak summer. Soil temperatures above 120-160°F (49-71°C) are generally sufficient to kill pathogenic (disease-causing) soil bacteria, fungi, viruses, and some insects.

A clear polyethylene tarp is a great option for solarizing. You don’t necessarily need to buy a new tarp for this use. You could reuse an old sheet of greenhouse plastic to serve the same purpose. Studies demonstrate success with both black tarps and clear plastic, but some disease spores are more effectively killed through transparent plastic.

Move Large Debris

One final use for a tarp is as a moving mechanism. This may seem obvious, but I’ve seen a lot of gardeners hurt their backs shoveling and hauling things that they could have just slid around on a tarp. You can place manure, compost, leaves, straw, prunings, and pieces of wood on a tarp and slide it around your yard as needed. You can even use a tarp to move large shrubs and trees.

Drawbacks to Soil Tarping

No garden “hack” comes without a few drawbacks. Tarping is convenient and technically chemical-free (far better than applying herbicides or fungicides!), but it still is not natural. A giant piece of plastic is still harmful to Mother Nature to produce and dispose of. The main downsides to tarping and solarization are the risks of harming beneficial soil microorganisms, the potential accumulation of microplastic chemicals in your soil, and extra plastic waste in landfills.

Harm to Soil Microorganisms

Soil microbes are sensitive to changes in temperature, and the microbial communities will be significantly altered after the soil temperature is raised so high. Fortunately, solarization primarily affects the upper inches of soil, and you should be able to preserve beneficial microorganisms in the layers beneath.

It is important to reincorporate healthy microbiota through compost, worm castings, soil inoculants, or compost teas added back to the bed after the tarp is removed.

Microplastic Contamination

There is a lot of concern about microplastics entering the soil ecosystem using this method. Microplastics are microscopic particles of plastic that can ultimately end up in our water, food, and in our bodies. Research shows that microplastics can damage human cells. 

Plastic degrades as it heats up, and solarization plastic is exposed to UV rays for extended periods of time. Most tarps are made of low-density polyethylene, which is considered a safer plastic for gardening because it isn’t known to leach chemicals into the soil or food. But it is still a synthetic petroleum-based material being introduced to your garden. If possible, source BPA-free and recycled plastic tarps. 

Plastic Waste

We can’t deny the truth: tarps are plastic, and we all know how harmful plastic pollution is to the environment. Humans have produced over 8 billion tons of plastic since the 1950s, and only an estimated 10% is recycled.

This synthetic material can take thousands of years to degrade and break into billions of tiny microparticles that are found in soils, animals, waterways, and even newborn human babies! Before you buy tarps for your garden, consider how long the plastic will last and what will happen to it when you’re done.

The Most Eco-Friendly Way to Tarp is to Reuse Existing Plastic

Ultimately, the choice to tarp is up to you! These large sheets of thick plastic are highly useful in the garden, but it helps to weigh the environmental impact before we purchase anything new. If you already have a tarp lying around that you’d like to reuse, I think it is a sustainable way to reduce tillage and chemical use in the garden. It is especially great to reuse old greenhouse plastic or an upcycled tarp purchased from a thrift store.

However, if you are planning on purchasing a new tarp, you may want to try out mulching, cover cropping, or another biodegradable mulch before investing in a huge piece of plastic. If you still want to buy a new tarp, make sure to take really good care of it so it lasts as long as possible. Don’t use anything that might poke holes in the tarp, and always fold it up when not in use.

Final Thoughts

Tarping is a simple, convenient, and passive way to reduce weed pressure and plant diseases in the garden. They can also speed up the decomposition of crop residues and warm the soil in the spring.