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Can You Add Too Much Compost To Your Soil? The Facts!

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compost with worms in hands

Some gardeners will decide to start and keep a pile of compost on their property because they are unsure of using commercial chemicals and fertilizers for their growing garden. But, as great as compost is for your garden, is it possible to have too much of a great thing?

In this case, yes, there is such thing as too much compost. Too much can be harmful to the soil and plants, especially manure compost. But why? What is it about too much compost that can be harmful to plants?

Wide range of benefits for plants and soil in a garden from adding compost

Adding compost for Soil Fertility Improvement

Compost supplies the essential nutrients that plants need to grow because of the well-decomposed organic material within it. These nutrients include phosphorus, potassium, nitrogen, as well as micronutrients.

Soil Structure Improvement through adding compost

A stable form of organic matter is added to the soil when compost is added. As a result, the moisture-holding capacity is increased in the soil. Soil that has become compacted or is too sandy can be improved because of the compost.

Adding compost also aids in Soil Health Improvement

Compost contains microorganisms that are beneficial to the soil. Nutrients will become more available to plants because of these microbes. In addition, when these beneficial organisms’ number and activity level dominate the soil’s environment, they also suppress the pathogens within it.

After reading this, you are probably wondering, “why wouldn’t I need to use more compost in my garden?” Of course, these benefits are great for any garden.

The answer really does depend on what your individual lawn or garden needs. Different nutrient levels and soil types come with every garden – maybe even different pH levels.

Soil tests are always recommended to construct the best soil amendments for your yard and gardening goals.

A working garden will require water, plenty of sunshine, plant nutrients, soil that is a good rooting environment, along with good weed and disease control. But, when adding new plants to a garden bed, it can be difficult to know if you need compost – or how much. So, let’s discuss what compost is.

The video below shows you exactly how to make nutrient-dense compost perfect for adding to your garden soil. Watching this video will teach you everything you need to be successful every time.

What is Compost, and why should we add it to our soil?

Compost is something that many gardeners swear by because of the many benefits that it offers to their gardens. It is an organic matter that is made with materials such as shredded twigs, leaves, plants, and even kitchen scraps.

Instead of paying a company to clean up and haul away any dead plant matter, composting is a great way to save money by recycling any yard waste that would have ended up at the landfill in plastic bags.

Gardeners give their plants a boost by giving them all of the nutrients they need to incorporate compost into their gardening routine.

However, using too much compost will harm plant growth or kill it. This is the unfortunate dark side of compost use.

The Dark Side of Adding too much Compost

As we know, adding compost sounds like the best possible thing to add to any garden to add nutrients from the decomposed plant matter. Over time, plants will use up the nutrients from the topsoil in the garden or the planting pot they planted, so adding compost would be ideal, right? Well, that’s not always the case.

Yes, compost adds nutrients to the soil, but compost is not a fertilizer, as few gardeners will know. Unlike commercial fertilizers, compost isn’t a ready-made form of adding energy back into plants.

Nutrients such as nitrogen and phosphorus are added to plants from compost, and however, uncured compost can turn deadly.

As it may be very tempting to use uncured compost that consists of organic plant matter, the truth is it will contain seven times more phosphorus than any plant would need. When too much phosphorus is absorbed, it becomes poisonous to a plant, even though smaller amounts of phosphorus are vital. The same can be said of compost that is made of manure.

Why Adding too much Compost can Become Deadly To Plants

Too much compost can be poisonous due to higher phosphorus levels if the compost is not fully cured, even though it can be a great source of nutrients and builds the structure of the soil.

High phosphorus levels will make it harder for plants to absorb iron and manganese; this will result in deficiencies causing chlorophyll in the plant leaves to leave the plants veins and be trapped on the outside. Too much iron or phosphorus can be the cause of this. You can add to this problem by adding more compost and end up killing your plant.

Mycorrhizal fungi are a vital part of the plants’ microbiome; high levels of phosphorus are toxic to mycorrhizal. These fungi supply the plant with water, phosphorus, and nutrients. Without it, plants must use more energy, which larger root systems need to survive.

The Four Stages of Compost and what happens to the soil when we add them

Before it becomes useful to gardeners for their garden, compost goes through four curing phases. These phases are:

  • The Mesophilic Phase
  • The Thermophilic Phase
  • The Cooling Phase
  • The Curing Phase

To understand why compost can be bad for your plants, let’s take a look at these phases.

The Mesophilic Phase of Compost

At this phase, bacteria combine oxygen with carbon to form carbon dioxide and energy within the compost piles’ formation; that energy is then used for growth by microorganisms. Any leftover energy then leaves the pile as heat.

The compost pile temperature will rise to 111 degrees Fahrenheit during this first phase due to the proliferation of mesophilic bacteria. In this phase, mesophilic bacteria can include E. Coli and other bacteria that are harmful to humans; these bacteria are overcome by the heat when it nears 111 degrees Fahrenheit to around 125 degrees Fahrenheit.

The Thermophilic Phase of Compost

The rise in heat during the previous phase brings in the thermophilic phase. This is where the microorganisms become very active and begin to decompose the matter within your compost pile and creates even more heat in the process.

During this phase, the temperatures within the pile can reach up to 158 degrees Fahrenheit. This phase only lasts a few days to a few months and will become localized in the area where new material has been added to the pile.

The compost pile will only have a few nutrients available at the end of the thermophilic phase. However, there is still an enormous task for the microorganisms since there will be much organic matter left in a pile to digest and become useable compost.

The Cooling Phase of Compost

After the thermophilic phase, materials will be left behind that were resistant to the rising heat; microorganisms left during this phase will return to the compost and start digesting these heat-resistant materials. This is called the cooling phase. Macro-organisms such as earthworms and fungi are vital for the formation of rich compost. These organisms will break up these coarser elements and move into the pile.

As a matter of fact, the soil would be very coarse and tightly packed if it wasn’t for earthworms. They are a vital part of topsoil composition. In addition, there would be no way of supporting plant life within the soil if it wasn’t for earthworms; this is because the soil wouldn’t have any aeration, and the earthworms’ feces make an excellent fertilizer.

The Curing Phase of Compost

This phase of the composting process is a long yet vital one. Gardeners, unfortunately, can become very anxious and no longer want to wait for their compost to fully mature.

The curing phase makes the soil healthy for consumption. This phase is a safety net that assures pathogens harmful to humans and has died off.

When a gardener is unwilling to wait, compost at this phase can be deadly to some plants. Substances that are toxic to plants, such as phytotoxins, are produced from uncured compost. They contain elevated levels of organic acid and will rob the soil of nitrogen and oxygen.

Adding Compost is like adding Fertilizer, Almost.

Only when grown in a gardener’s backyard, can compost be considered as a fertilizer. However, it’s legally not considered a fertilizer when manufactured by anyone else.

When grown in the backyard, compost is a fertilizer because it’s organic, and through the phases we just discussed, the bacterium and fungi in a heap result in a slow release of nutrients.

Even though compost can return nutrients to poor soil that plants need to stay healthy and grow, it is not the only answer to soil problems.

An amazing resource titled composting for beginners in the garden’ also covers information, details, and tips as to what makes compost and using it.

Is There Such Thing As Adding too Much Compost?

wheel barrow of soil

Some reputable, experienced gardeners will say this. They will say this because most gardeners and farmers are always having a hard time producing enough compost. So, having too much can be very hard to imagine.

As we have already discussed, it is quite obvious why smothering a lawn or garden with compost is not a very good idea, even if you decided to smother it with organic compost. But, more compost will actually smother the grass or plant, at least the part that is closest to the ground. If you damage that part, you’ll run the risk of losing the whole thing.

Gardeners and landscapers will frequently hear that trees and shrubs being transplanted should be backfilled with amended soil (soil mixed with organic matter). However, if a mature tree’s roots will not reach where the hole has been dug deeper, organic matter is wasted.

What happens to the soil if we add too much compost

Also, if too much organic matter is used, the soil will decay as it subsides. Finally, water problems will result when the amendment creates a sharp delineation between unamended and amended soil.

Unlike most fertilizers, the nutrient content of other organic amendments and compost is much lower. Therefore, there is a huge and slowly released nutrient load when compost is mixed with soil at a 1:4 ratio or higher.

Nutrients that are already in the soil will have added nutrients and will even receive a boost in the activity of microbes when compost is added. Therefore the nutrients added by compost far exceed those that are actually in the soil already.

Experienced gardeners will often not know that good soil will contain only approximately 5% organic matter by weight, equivalent to about 10% by volume. Thus, just like anywhere else, it is possible to overdo a good thing in the garden.

So, you may want to think twice if you are considering adding more compost to your garden. You may find that it has actually done more harm than you intended.

Conclusion on Adding too much Compost to your Soil

Just like most things in the world, too much of something can cause further problems. This can be said too when adding too much compost to your soil. In this case, it brings more harm than good to the soil and plants, especially if it is manure compost.

Before putting in too much and risk all the harm to your beloved plants, it is highly suggested to study first what exactly your garden needs and knowing the soil’s ph level by doing soil tests.

We have a detailed article on the importance of soil testing, and you must know what your soil is lacking before amending it. You can view that article here, so you know exactly what’s required.

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