Can Plants Grow In Compost Only?

All gardeners have to use compost or leaf mold in their garden. Compost is an excellent addition to the soil. It adds nutrients to the soil and improves the soil texture.

More often than not, you have to mix compost with soil for it to work effectively. But can plants grow in compost only?

Well, growing your plants on compost only is not advisable. Naturally, compost is light; hence has poor drainage properties. Thus, water drains extremely fast in compost.

Also, since compost is light, it does not offer a robust support system for the roots. There are so many reasons explaining why you cannot grow plants in compost.

Why can’t you grow plants in compost only?

  • Compost dries out faster:

Generally, compost has poor drainage properties. Compost cannot retain moisture for long periods; hence, it is more likely to dry out faster. Consequently, plants won’t be able to get enough moisture when grown in compost only.

However, if you mix the compost with soil, it fosters excellent water retention. Therefore, your plants won’t dry out faster. All in all, compost dries out quickly; thus, it is not advisable to use it alone to grow your plants.

  • Compost is costly:

The massive costs involved in buying compost can be a turn-off to most gardener beginners. Fortunately, you can use homemade compost. Making compost by yourself helps you save money.

Using compost only to grow your plants requires you to purchase it in large quantities. And this can cost you a fortune. So, it would be best to mix planting soil with compost. This way, you’ll be able to improve the quality of your soil.

  • Compost does not offer strong support:

Your plants won’t have a steady support system when you use compost to grow them. This is because compost is soft and light in texture. Chances are high that the plant won’t survive in the compost, especially when it grows bigger. On the other hand, mixing the topsoil with compost provides a robust support system for your plants.

  • Compost will compact quickly:

When you add water to compost, it shrinks quickly. Compost compaction blocks the pores in the soil. As a result, your plants won’t receive maximum aeration. Not to mention, nutrients won’t be able to travel properly through the soil to the plant.

Subsequently, your plants start becoming weak and changing color. Compost compaction also attracts plant diseases like root rot. Luckily, if you mix soil with compost, peat moss or leaf mold, you won’t encounter this problem. Compost usually improves the drainage and water retention properties of the soil.

  • Compost will lead to excess nutrients:

You should not grow in compost only because compost carries excessive nutrients. Plants thrive when they receive the proper nutrients. However, when these nutrients are in excess, they can damage the plant. Compost usually contains phosphorus, sodium, iron, nitrogen, magnesium, zinc, and manganese.

The nutrients in compost are usually more than what the plant requires. Therefore, nutrients can accumulate in the soil and eventually become toxic to the plant.

Excess nutrients lead to yellow leaves and destroyed fruits. Conversely, if you mix compost with planting soil, it provides a good balance of nutrients. In turn, your plants will develop healthy leaves, roots.

Can you start seeds in compost?

Once you start planting seeds, you need to take good care of them until they germinate. New seeds need proper and constant care. Mostly, you’ll only need to use soil and water to enable the seed to germinate. Can you apply compost at this point?

Gardening experts do not recommend applying compost on young seeds. As seen earlier, compost contains excess nutrients. These excess nutrients can burn the growing roots if you are not careful. Also, note that seeds usually have nutrients until they germinate. After germination, they will require nutrient supplements.

All in all, you don’t require providing nutrients to seeds in their early stages. All you need to do is water them appropriately. Seeds grow best in a quality sterile potting mix that does not contain any harmful microorganisms.

Can too much compost hurt plants?

One of the best things you can add to your soil is compost. Compost improves the quality of the soil. Thus, it helps you boost the healthy growth of your plants. But does applying too much compost hurt plants?

Typically, using excess compost hurts your plants. In particular, manure compost can damage healthy plants when applied in excess amounts because it contains a higher amount of phosphorus.

What does a plant need?

First, let’s understand a plant’s requirements. Keep in mind that plants are different, so they have different requirements. But generally, crops need an NPK ratio of 7-1-5.

From this, it is clear to see that plants often need low phosphorus levels to thrive. Phosphorus levels should be approximately seven times less than nitrogen.

The problem with too much compost

Manure-based compost contains a higher amount of phosphorus. Therefore, be careful not to use excessive amounts of this.

Nitrogen and Phosphorus in Soil

When you apply nitrogen to the soil, it penetrates the soil faster to reach the plants. At times, nitrogen gets converted into N2O, hence escapes into the air. Rain can easily wash away nitrogen from the soil. If you apply excess nitrogen, it forms a layer on top of the soil.

On the flip side, phosphorus penetrates the soil slowly. Unlike nitrogen, phosphorus is rarely converted to gas that escapes to the air. Also, rain does not wash phosphorus away easily. As a result, phosphorus is more likely to accumulate in the soil. Excess phosphorus will always build upon the soil.

Both plant-based and manure-based compost can lead to an excess layer of phosphorus in the soil. Once phosphorus accumulates in the soil, it becomes toxic. Hence, it damages healthy growing plants.

What happens if phosphorus levels get too high?

When there are high phosphorus levels in the soil, the plants won’t be able to absorb manganese and iron. Subsequently, plants will lack these essential nutrients.

And this can lead to interveinal chlorosis. Contrary to popular belief, you don’t need to add more iron to the plant to solve this problem. In fact, if there is excess phosphorus in the soil, iron is the last thing needed by your plants.

Additionally, excess phosphorus destroys beneficial microorganisms in the plant, like mycorrhizal fungi. This fungus fosters a healthy distribution of nutrients to your plants.

If your plants lack mycorrhizal fungi, they will struggle to develop a robust root system. Also, they won’t have the energy to produce large and healthy flowers and fruits.

Plant-based compost or manure compost?

Plant experts usually advise using plant-based compost instead of manure-based compost. This is because manure-based compost often leads to excess amounts of phosphorus in the soil.

You should apply about one inch or two inches of compost to your plants annually. At times, you may require using more; it depends on the requirements of the plants.

How much compost do I add to my soil?

As mentioned earlier, using compost to grow your plants is a good idea. Compost fosters the growth of healthy plants. Gardeners usually use compost to improve the quality of the garden soil by enhancing water retention and texture of the soil.

One of the main advantages of using compost is that it works gradually. Therefore, one compost application can keep your soil healthy for a long time. So, how much compost do you add to your soil?

Quantity of compost to use on your plants

Gardening professionals recommend using 0.375 to 0.5 inches of compost on topsoil. However, if you plan to change the soil structure using compost, apply one to two inches. Compost should never exceed 30% in the garden soil. In planting pots and raised beds, compost should never exceed 25%.

The exact amount of compost your plants need usually depends on various factors. More often than not, the number of nutrients present in the soil will determine the amount of compost you need. If the soil already contains too many nutrients, consider using less compost.

It would be best to conduct a soil test to check the nutrients required in the soil. This way, you’ll know the amount and type of compost to use. The plant type also determines the amount of compost you need to use in the soil.

Importance of adding compost to your garden

Below, we take a detailed look at some of the benefits of compost to the soil.

  • Adds nutrients to the soil:

Basically, compost is rich in nutrients. Adding it to your soil improves the nutritional content of your soil. Compost often adds nitrogen and carbon to the soil.

The nutrients that compost offers are good for promoting healthy plant growth. Also, since compost boosts the quality of the soil, it fosters the faster transfer of nutrients to plants.

  • Adds beneficial microorganisms to the soil:

Compost and leaf mold breaks down into the soil over time. Living microorganisms like worms are often primary ingredients in compost. Once released into the soil, they foster proper aeration in the soil.

And this speeds up the composting process. Subsequently, plants are able to get the required nutrients at the right time. Beneficial microorganisms in the soil also protect the plant from a broad spectrum of diseases.

  • Recycles kitchen and yard waste:

You won’t have to spend much on buying garbage bags making homemade compost. This is because more than 30% of your kitchen waste comprises organic material you can use for your compost. Also, using kitchen waste as your compost ingredients means you won’t have to take out your trash bags as often.

Good for the environment! Using organic compost is a great way to conserve the environment. Rather than using synthetic fertilizers and pesticides, use compost. They protect the soil from pollution. As a result, they keep the water bodies around the area safe for human use and aquatic life.

Final thoughts

Plants cannot grow in vermicompost or compost only. Compost is light; hence it has poor water retention properties. Also, compost cannot support the root system of a plant. Compost and vermicompost always works better when mixed with topsoil.