To cover or not to cover – gardeners have been asking this question for centuries, and there’s never been a clear answer. Protecting your garden with plastic offers many benefits, but it also has disadvantages. So, covering your garden with plastic may be the best option for some people, while it may be unnecessary for others.
You should cover raised garden beds with plastic to keep your beds from eroding and compacting over winter. Plastic will also prevent weeds and increase soil humidity in the growing season. Depending on your needs, you can create a plastic tent or directly cover your bed’s soil with plastic.
Methods of Covering Your Garden Bed With Plastic
Before we get into the details and advantages of covering garden beds with plastic, we need to establish a few things. There are two main methods for covering garden beds with tarps and sheets; each is better for a different season.
So, let’s examine these methods and discuss what they can do for your garden beds:
Placing the Plastic Directly on Your Soil
Placing plastic sheets directly on top of your garden bed’s soil is a fantastic way to protect the soil’s moisture retention, fertility, and bacterial balance during the coldest months. However, covering the bed during spring or summer also has some benefits.
A layer of opaque plastic will trap humidity into your garden bed, helping decompose your fertilizers (such as compost, leaves, mulch, or manure), enriching the soil. As this decomposition occurs, your beds will become warmer than the ambient temperature outside, which can help keep the healthy pH-balancing bacteria in your garden alive and happy.
Since this plastic sheeting keeps your garden beds warm, people often use this bed-covering method in winter to ensure that the beds don’t become infertile or overly dry.
This covering method also decreases soil compaction rates and fertilizer runoff, keeping your raised beds in the best condition possible.
For more information about how this method works and what it looks like, you might want to watch this video from a fellow gardening enthusiast, Gary Pilcharick, at The Rusted Garden:
Creating a Bed Cover or Canopy With Plastic
A garden bed cover is a dome or tent that you place over your garden bed. Bed covers like these function like greenhouses, and they are usually clear plastic tarps staked up with ropes or tent poles. Most people use these in the spring or summer to raise the humidity and temperature in the bed.
These “tents” can also keep rain from beating down your garden, protecting your plants from wind and rain damage. In addition, since the rain will not hit your soil directly, you will reduce soil compaction and fertilizer runoff, making garden maintenance more manageable in the long run.
If you would like to see this process in action, check out this tutorial from Hoosier Homemade:
The Pros and Cons of Covering Raised Garden Beds With Plastic
Covering your garden beds with plastic is a slightly controversial method of keeping your raised garden beds in their best shape. That’s because, in many cases, the cons can outweigh the pros.
So, let’s get to the root of this controversy and look at the plain benefits and disadvantages of using plastic sheeting or tents on your soil.
Pros
Insulation, Higher Bed Temperature, & Raised Humidity
Plastic is an ideal insulator for garden beds that need protection from cold weather. Both methods of laying plastic over your garden beds will also increase the soil’s temperature while trapping in humidity, protecting your plants from breezes and cold weather.
Clear plastic is also a fantastic alternative to glass windows for creating a makeshift greenhouse that traps humidity and keeps your plants warm.
Blocks Pests, Weeds, & Diseases
Plastic can keep insects and animals away from your garden.
Meanwhile, covering beds in the summer can kill pathogens and infection-causing bacteria and fungi. If you have experienced an infection in your garden beds, covering the soil with plastic to increase the heat can help you re-balance the soil and “burn out” the infection.
A plastic barrier can also prevent weeds from seeding and creeping into your garden, so you won’t have to spend as much time weeding when you use plastic.
Inexpensive
If nothing else, plastic tarps are both affordable and versatile, so they are both cheap, and you get a lot of bang for your buck.
Reduces Soil Erosion & Compaction
Plastic can trap your soil in your garden beds, ensuring that your planting media will not wash or blow away during windy or rainy weather.
The impact of rain on your garden beds can also press down the soil; over time, the planting media may lose aeration and become compressed. Tarps protect from rain droplets, keeping your soil as fluffy and airy as possible.
Less Fertilizer Runoff
If you want to ensure that your raised beds’ fertilizers and soil amendments stay in the raised bed, plastic can help. Lining the sides of your beds with plastic or covering the top can ensure that your fertilizer does not wash away from the topsoil, protecting your soil’s quality and the environment.
Cons
Not Biodegradable
Unfortunately, plastic takes many years to break down in the soil, so it is not a sustainable material, nor is it environmentally friendly.
Inhibits Water Flow & Decreases Airflow
Plastic coverings can increase soil moisture too much, leading to waterlogging and root rot. Plastic garden bed covers may also reduce airflow, facilitating the growth of potentially undesirable anaerobic bacteria and fungi in your soil.
When Should You Cover Your Raised Garden Beds With Plastic?
You should cover your garden beds with plastic in the fall after harvest season and keep the bed covered until after the last frost of winter. You can also use clear plastic bed covers while germinating your seeds to help acclimate them to the outdoors.
Covering your garden beds while nothing is growing will ensure that your soil retains its fertility and moisture while waiting for the temperatures to increase. Then, once it’s time to plant, you can leave the tarp on your beds for a few weeks to help you acclimate your plants to the outdoors.
This method will keep your seedlings warm and ensure the soil stays moist, making seeding your plants much more manageable.
If you use a clear plastic bed “tent” or cover, you might want to put the tarp back on during the early fall to extend your harvest season and protect fruits and veggies from pests.
Tips for Covering Garden Beds With Plastic
So, while covering up your raised garden beds can be incredibly practical, there are still some unwanted side effects that you’ll need to prevent.
Here are some tips to help you reap all the benefits while warding off the disadvantages:
Remove the Plastic on Particularly Hot Days
As I mentioned above, plastic is an insulator that can trap too much heat for some plants. So, you may need to remove plastic bed covers while the weather is warm and sunny to prevent overheating and protect your plants from wilting.
Don’t Line the Bottom of the Beds With Plastic
Since plastic is not porous and will trap water inside your raised garden beds, lining the bottom will eliminate drainage areas, causing the soil to become muddy and boggy. These conditions may kill plants, introduce fungal infections, and invite pests to establish colonies in your garden beds.
Allow Some Airflow
When using plastic in any garden, increasing aeration is critical. Plants need air to grow, and your soil needs to “breathe” to encourage the growth of healthy bacteria and promote water evaporation.
Use an awl, scissors, knife, or a pen to poke small holes all over the plastic before covering your garden bed for the best results. Alternatively, you can cut slits in the plastic to allow airflow.
Regularly Check the Bed’s Humidity Level
Check your beds frequently and lift the plastic when necessary to ensure that your garden beds do not become boggy and muddy.
If you follow these tips when covering your garden beds, you won’t have to deal with any issues related to using plastic in gardening. So, give it a shot and see what plastic can do for your crops!
Final Thoughts
Covering raised garden beds with plastic is a good idea if you take precautions to avoid overheating your garden, inhibiting airflow, and trapping in too much moisture. For the best results, use plastic covers to aid in heat retention and composting during the winters. Then use clear plastic coverings in early spring to keep your seeds warm and help them grow.
You can also use plastic coverings to keep pests out of your garden beds and warm up your plants during the harvest season.
If you’re still in the process of planning your raised beds, check out my article Do Raised Garden Beds Need to Be Staked?
