Using Compost on Top of Soil: The Pros and Cons Explained


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Looking for an organic, natural way to make your soil healthy so that your plants can thrive? Adding compost directly on top of the soil will create both healthier soil and bigger plants.

When using compost on top of soil, it should be applied in a 2 – 4 inches thick layer. Compost contains bacteria, fungi, microorganisms, and nutrients that promote plant growth. Additionally, using compost as a soil cover prevents weeds, insulates the soil, and helps prevent moisture loss from the soil beneath.

In this article, we will explain the benefits of applying compost on top of the soil which can benefit both potted and garden plants and would remove any concern you may have when using it.

The Benefits of Adding Compost on Top of The Soil

Compost on soil

Compost is a great thing to add on top of the soil. It’s rich in nutrients and other goodies that plants love, and it feeds the soil beneath it, adding yet other nutrients and benefits. With compost, plants get lots of healthy, natural stuff without the need for potentially toxic chemicals.

Compost can be applied in a 2-4 inch layer of compost mulch over the soil. This will benefit your soil and plant greatly.

Here’s how:

  1. Compost mulch is no less than a sponge. It retains moisture in the soil. Strangely enough, as the soil dries up, the compost breaks down into humus and releases moisture slowly. It prevents soil evaporation and saves plant roots from drying out even in summer.
  2. It smothers weeds from sprouting out by shading out sunlight. Weeds are harder to kill when they have access to sunlight.

    Forming a layer of soil on top of the weeds will stop sunlight from reaching them, making them harder to grow.
  3. Adding compost on top of the soil also helps retain the vital nutrients that are crucial for photosynthesis & plant growth, such as nitrogen and carbon.
  4. Compost mulch quickly emits nutrients making it easier to be absorbed by plants.
  5. It regulates soil temperature. It sometimes raises the temperature whereas sometimes insulates the soil against temperature swings.

How Does Compost Benefit Soil?

Compost, being natural, is eco-friendly. It enhances the physical, biological and chemical properties of soil that ultimately stimulates healthy plant growth. Compost has a lot of efficacy. Let’s discuss some of them.

Improves Soil Structure

By adding compost to the soil, you feed plants with nutrients. The soil becomes smoother and crumbly, making it easier for roots to grow.

On the one hand, it helps retain water in sandy soil while it loosens up the compacted and heavy clay soil to make it easy for the roots to penetrate. This makes the plant grasp the soil even more and helps to prevent soil erosion.

Improve Soil pH

When compost is added to soil, it changes the soil’s pH level. This is a good thing. A higher pH level makes for healthier plants since more nutrients are available to plants in soil with higher pH levels. Acidic soil is perfect for flower and vegetable gardens.

The pH scale runs from 0 to 14. A strong base has a high pH level, while an acidic substance has a low pH level. In most soils, the ideal pH levels are between 6.0 and 7.0. 

Adding compost on top of the soil keeps up an ideal pH range in the soil that is favorable for the absorption of nutrients by plants.

Supplies Nutrients

Compost contains the 3 most crucial macro-elements such as phosphorus(0.6-0.9%), nitrogen(1-2%) and potassium(0.2-0.5%) that speed up plant growth. In addition, it also bears some trace elements that are often not provided by synthetic fertilizers.

Plant Disease Prohibition

Compost harbors soil bacteria and fungi that prevent different plant diseases. It also lessens the need for pesticides and fungicides, which are toxic to animals, humans, and even the soil biota.

Feeds Microorganisms

The microbial community, which helps digest organic matter and convert them into effective nutrients, is fed by compost. These microorganisms even help in nitrogen fixation.

Furthermore, compost can stimulate the growth of earthworms in the soil. The worms need food, and the more food there is, the more worms there are. Earthworms help the soil hold water, and they help break down the soil. 

You see, most soils have something of the texture of concrete, with particles too small to be broken apart by a shovel, but too big to be broken down by worms.

Adding compost to the soil encourages earthworms to grow to full size. Earthworms do a good job of breaking down large particles by eating them. 

Disadvantages of Placing Compost on Top of The Soil:

Besides the benefits, compost has a few drawbacks that should also be considered when applying it to soil for it to be truly effective.

  • Usage of specific food waste emits a foul smell while decomposing. This may affect the ambiance of your house by causing air pollution.
  • Compostable food wastes often invite rats and even snakes.
  • The procedure of decomposition involves the activity of bacteria. This may cause the spread of different diseases.
  • Composting consumes both time and energy. It also calls for enough monitoring. 

Compost or Topsoil: Which is Better?

Now, it is a bit difficult to take the side of a particular one as both have their respective advantages and disadvantages. Let’s see the contrast.

Compost is the decomposed organic material better for pots or hungry plants, whereas topsoil is the upper layer of the soil better for general gardening projects. 

While topsoil is better at retaining moisture for a longer period, compost is a slow-release fertilizer that excels in containing organic matters and nutrients.

Albeit cheaper, topsoil contains weed seeds and prior applied fertilizers and pesticides. On that note, although expensive, compost is full of beneficial organisms. 

Given the above, many things need to be taken note of to define a particular one as better than another. To get something better, you can combine the two.

When To Add Compost To Soil or Topsoil?

Compost is applied in any season if used as an amendment except when the soil remains frozen. 

If you use it as fertilizer, you will be required to apply a 2-3″ layer every year.

Now, in case it’s bagged compost, consider applying a 1-2 inches thick layer in the early spring. For homemade compost, it is effective if used in autumn. 

By spring, the compost will be decomposed. Keep adding a 2-3 inches layer of this compost so that it gets the winter season to be decomposed to make the bed ready for planting.

Should Compost Be Mixed into The Soil?

The mixture of compost and soil is undoubtedly an elixir for your plants. But, still, it is not always applicable.

When your soil is of a good texture, you can just put a layer of compost on the upper surface a little away from the stem. In such a case, digging the soil to mix compost with it might disturb the beneficial mycorrhizal fungi, which have a major role in helping plants access nutrients from deep down the earth. 

You can mix compost with soil when you are making potting soil at home for your plants.

The Takeaway:

Adding compost on top of the soil is one of the best things you can do for soil. It improves soil structure, decreases hardpan and compaction, improves drainage and aeration, increases nutrient levels and microbial life in the soil, and generally enhances the overall health of the soil. Plus, it’s really easy- you can make compost at home with ‘green’ waste from your yard!

In short, adding compost on top of the soil is the most hassle-free as well as effective way. Just keep up a certain distance between the stem and the mulch to avoid spreading various diseases

JayLea

JayLea has a passion for plants and has been gardening since 2015. He has valuable knowledge about gardening and houseplant care and can answer everyday practical questions that every plant owner has.

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