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Does Soil Need Sunlight? Here’s Why Not & Soil Protection

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Having soil unshaded can become an issue because sunlight can kill living organisms and remove moisture from the soil. However, both garden and potting soil can be covered to provide shade against the scorching effects of the sun.

Soil does not directly need sunlight. The fertility of soil depends on the climate, air quality, water, and organic matter. However, sunlight directly affects the living organisms in the soil like Cyanobacteria, Algae, etc. These organisms require sunlight to produce carbohydrates, which benefit the soil.

But that’s not it! All of this may sound so easy and simple at first, but that is not the case. There are several factors as to how the soil is affected by sunlight.

Following are the factors which provide detailed insight into the effects of sunlight on the soil.

How Does Sunlight Affect Soil:

does soil need sunlight

As mentioned above, Sunlight doesn’t directly affect the soil. Instead, it affects the microorganisms above or below the surface. Cyanobacteria and Algae are some of these microorganisms.

These organisms synthesize essential nutrients for the soil, such as Carbohydrates. Sunlight plays a vital role in making the soil fertile for plant growth.

Sunlight helps plants in photosynthesis, where plants produce their food with sunlight, and the more photosynthesis, the more the benefit for the soil.

Then, come the solar radiations, the scorching heat which travels from the sun to the earth and is absorbed by the soil, which increases soil temperature.

An increase in soil temperature can either be good or bad. It can either instantly kill the microorganisms inside or increase the number of nutrients in the soil.

Simply put, warm soil proves to be more fertile than cool (low temperature) soil.

Micro-organisms are more active in warm environments than in colder ones.

Too much sunlight will cause excess water evaporation from the soil, and as a result, the soil particles will dry out and begin shrinking, pulling away from each other

This is evident as seen in arid areas where there are large and evident cracks along the soil surface. However, these effects are confined to arid regions and can also affect garden soil and lawn areas.

Do Microorganisms in Soil Need Sunlight?

Now that’s a YES, they do. But how? Although organisms like Bacteria need relatively less sunlight to grow and synthesize the necessary nutrients by soil.

A study found out that bacteria can actually tell light and dark apart. So the sunlight can make bacteria even more dangerous.

However, Algae and Cyanobacteria require more sunlight, almost the same as plants. They are photosynthetic. Cyanobacteria are said to be one of the oldest forms of life and one of the reasons for oxygen on earth.

Sunlight is the most abundant energy resource on earth, renewable as well. But, of course, microorganisms require sunlight to grow in the soil as well.

The growth of Algae is dependent on sunlight. Therefore, ponds or water bodies that are more exposed to sunlight tend to have more algae growth than less sun exposure.

These microorganisms like Algae possess chlorophyll to convert sunlight into chemical energy, which directly affects algae growth.

Stripping algae off the sunlight can result in their death. 

All in all,  microorganisms like algae and Cyanobacteria need sunlight for their growth and development. 

Does Sunlight Cause Weeds to Grow on Soil?

YES, the sunlight does cause weeds to grow on soil. However, weed seedlings can grow exceptionally well when exposed to sunlight. Weed, AKA Marijuana, is a member of the Cannabaceae family. These family plants are either male or female.

Weed plants require organic matter-rich soil to grow. In addition, they need approximately 10 to 13 hours of direct sunlight.

In other words, these plants are happiest when exposed to sunlight. Marijuana plants don’t just require constant sunlight but also keep control of different wavelengths of light.

Like other plants, Marijuana plants also have chlorophyll for converting light into food energy. So simply put, If you want your Marijuana or Cannabis plant to grow exponentially, you need to put it in sunlight all day till sunset.

Will Using Fabric or Mulch To Prevent Sunlight, Affect It?

Covering the soil with mulch may prove good for the soil, but covering it with fabric or landscape fabric might be the last thing you want to do.

Landscape fabric has more cons than pros when it comes to covering the soil with it. 

Covering the soil with fabric prevents rapid weed growth on soil. It also decreases the weed control need and keeps the soil moist. However, as time passes, the decomposed soil particles block the cloth holes, making it difficult for the required amount of water to reach the roots, resulting in the plant’s death.

It also prevents the earthworms from oxygenating the soil, which leads to unhealthy soil. Marijuana can still develop in mulch above the fabric.

Now, if we look at Mulch, that’s a relatively different story. Mulch also helps keep the soil moist, allowing healthy contents to reach plant roots, meaning healthy plants.

The Benefits of Mulch

  • Keeps the soil from losing water by keeping the soil moisture. 
  • Prevents rapid weed growth as well, and most importantly, it 
  • Protects the soil from harsh temperatures, especially from cold.
  • Consumes soil decay, which makes the soil even healthier

The Benefits Of Soil Cover Against Sunlight


Does the landscape fabric allow water drainage? Yes, it does. But it is both good and bad news for you. How? Landscape fabric allows water through it as well as air.

You might find it beneficial to use landscape fabric first, but wait until you see soil decay blocking it either for air or water.

Mulch, on the other hand, helps improve the drainage of soil over time. It improves soil structure by breaking down slowly to help drain the water and keep the moisture.

Weed Growth

Landscape fabric is good but not ideal for decreasing weed growth. First, the fabric needs to be accessible to water and air. But still, as time passes, the soil decay will start to build up on fabric, allowing weed to grow on the fabric.

Thick mulch applied on weed areas prevents the weed from growing a second time. However, it first requires hand weeding to pull out weed from their heads by hand before it has the time to go back to seed and emerge a second time.

See our detailed article on removing landscaping fabric from garden soil.


Mulch keeps the soil relatively warm by capturing the sun’s heat and then directly sending the heat to the soil below. It may be good for the soil in winters, but not in summers.

As already warm soil gets warmer by mulch, it may prove to be unhealthy for the soil. Overheating is never good for anything, no?

Temperature doesn’t have much negative or positive effect on landscape fabric, for that matter.

Water Retention

Mulch is ideal for water retention in soil. It is the primary feature of mulch. Simply put, If you cover the soil with mulch, it prevents direct sunlight, which results in relatively more minor water loss.

As for landscape fabric, it is not made to keep water. Instead, it is water permeable, allowing moisture to escape and enter through it without much effort.

The idea is to block the direct rays of the sun from hitting the soil?s surface. This actively prevents large amounts of moisture from being drawn away from the soil.

Soil Pests

Mulch has been ideal in several ways mentioned above, but here? Not so much. Mulch can be a perfect home for soil pests to exist and reproduce.

Applying mulch so close to your house may not be the best decision as it allows your little hidden enemies to make their way into your home.

Will Covering Soil Prevent Weeds?

A Big Yes! It will. Covering the soil with plastic sheets will kill the weeds leaving you with good garden space. You can use landscape fabric here by putting it on bare soil around tree trunks.

It will block the weeds and their growth and allow the water and essential nutrients to pass through them.

Apart from sheeting materials soil can also be covered with rocks and sand which has their own unique benefits.

Rocks can be used to cover the topsoil in potted plants because it prevents water loss, pests, weeds, splashing, and soil loss when the soil is being watered and pets from interacting with the soil. 

Sand, when used as a mulch, increases the aesthetics of the garden by contrasting the greenery of the plant with a white background. It also prevents weed growth and protects the topsoil from water loss and pests like gnats and fungus. Additionally, it can be used as an amendment that helps increase soil drainage and aeration.

The Takeaway:

Underground, in the dark, the soil doesn?t need direct sunlight to maintain life. The roots of plants and microorganisms below the surface feed off organic molecules and methane in the soil. 

However, soil contains a huge number of microorganisms, which do need a sufficient amount of sunlight for their growth and to maintain soil fertility (somehow). 

Living organisms in the soil, such as cyanobacteria, algae, and fungi, depend on sunlight to produce carbohydrates that benefit the soil.

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