Compost or Fertilizer: what should you use?

compost ready for use

When you grow your own vegetables and fruit it is good to get a return for your effort and monetary inputs. The return is more important when you approach gardening with a self-sufficient mindset, as we do.

Personally, we are prepared to do the work to make our compost on site and see it as a way of lowering costs while improving the soil. It can be a lot of work, and while we find it enjoyable, the question about using compost or fertilizer lingers.

This article is here to explain our thoughts on both compost and fertilizer and when you should use what. As self-sufficient growers who use organic practices, we take this subject seriously. Read on to see why.

Should You Use Compost or Fertilizer in Your Garden and on your soil?

Every gardener will eventually face this question, and we are no different. There are many nuances to the compost versus fertilizer query and hopefully we can address them here. It is also too simplistic to brand all fertilizers the same because they all have different components to serve select situations.

Compost on the other hand is not so individualized, generally speaking. Compost can be a simple recipe of dry vegetation and green plant waste, and time will convert these materials into compost in the right conditions.

Having said that, to expect compost to be beneficial, the materials used in making the compost should be the best available, and as diverse as possible. The ultimate benefit from adding this kind of compost to soil is the explosion of beneficial lifeforms that we introduce to the soil, and these lifeforms give stability and fertility to our garden soil. We reap the rewards through nutrient-dense foods, all from compost.

If the materials used in the compost recipe are low in nutrients, then why would the gardener expect the compost to grow great vegetables? To dig deeper into using either fertilizers or compost we need to first understand the differences between them, because they matter.

What is the difference between compost and fertilizer?

There are several important differences between compost and fertilizer, and we have them listed below.

  1. Compost is an all-natural organic material, created by natural processes.
  2. Fertilizer is manufactured using industrial processes.
  3. Compost is full of beneficial micro-organisms that partner with plants.
  4. Fertilizer is lifeless and sterile.

We expand on these below.

What are fertilizers?

Fertilizer is a product that is the result of a manufacturing process. The term “fertilizer” is a term that encapsulates many varieties of chemical and mineral mixes. It can be in the form of granules, powders, and liquids. Fertilizer is an engineered product so is available in every form that is useful.

The green revolution allowed humanity to grow crops with precision, using fertilizer blends dedicated to that particular crop. Fertilizer is part of an incredible process that has allowed humanity to leave the agricultural areas and develop many other industrious lifestyles.

One of the major changes fertilizer and the industrial growing process allowed is farming of soil inherently low in fertility. Previous to the advent of fertilizer farmland fertility was measured in worms per square foot. In fact, this is how land was once valued. This is not the case now. Soil has just become a substrate to support the plant from falling over.

What is compost?

Compost is both a natural product and a natural process. The material we know as compost is the product of the process we recognize as composting. The desired outcome of this process is an organic substance that holds some nutrients and a lot of tiny life-forms.

Many of the nutrients within the compost are bound up in the bodies of these microorganisms, and as these die the nutrients are released into the soil to feed plants. This is a basic description, because the technical version will take pages to explain.

Compost is a very deep subject that can get as detailed as you want it to be. Once you involve a microscope, as we have, every compost pile becomes a new world.

A good compost will inoculate the soil with these micro-organisms, and this is where compost shines. A good compost can be measured by the internal temperature of the pile as it progresses to maturity and being ready to apply to garden soil..

hot active compost
The microbial activity creates the heat. This compost pile is hot and active.

When I think about it, compost can be described in a short sentence. Compost is the final product of an expedited process of converting something that once lived into a form closer to base soil through rapid biological activity.

This biological activity requires nutrients and moisture, and this is why good composting practices include keeping the materials moist during the compost making process. If the process is progressing as expected, the compost runs hot for a week or more. Regular turning to introduce fresh oxygen into the compost pile is needed, though.

How do fertilizers work?

Fertilizer is a storable item, as you will note in any gardening center. It is generally shelf stable and will stay in this state until added to soil and water is introduced. Water is the key to any fertilizer success, as it is both the key to unlocking the elements within and is also the pathway for entering the plant.

Many granular fertilizer types have a coating on the outside, a casing if you will. This casing is soluble and is often manufactured using salts. Some of these salts are cadmium based and have environmental concerns of their own.

These granules are applied to soil when planting and wait for watering or rainfall. This moisture triggers the process of releasing the nutrients into the soil.

After water has dissolved the casing, the nutrients are now available to the plants. This is where fertilizer is very different to compost.

The nutrients in the fertilizer that have been released by moisture are now plant-available in liquid form, and the plants basically drink this nutrient soup from the soil.

This pathway for feeding the plant is completely different to that of compost. We describe the compost pathway further below.

Why is fertilizer cased in salt?

There are several reasons why the chemists who manufacture fertilizer choose salt with two important ones being stability, and dissolvability. The salt casing around the fertilizer is designed to remain stable while kept dry, and when soil moisture is present the salt attracts the moisture, the case dissolves, and this releases the nutrients.

If follow-up water is not available once the fertilizer casing has dissolved, damage can happen to the plants from chemical burning because the nutrient load is still concentrated and localized near the plant stem.

The timing of fertilizer application to soil and follow-up rain is critical, especially in the broadacre setting. The home gardener is likely to be actively watering, so this issue can be considered unlikely.

We know that much of the above does not apply to the gardener growing vegetables but understanding how a typical manufactured fertilizer works is vital to plant health, good harvests, and productive soil.

Do fertilizers have any disadvantages?

Suppose you have to apply this product to your soil every season without fail; the costs can mount, and the workload never diminishes. We consider this a disadvantage.

Once the fertilizer casing has dissolved, there is a limited amount of time for the plant to take up the nutrients before the wash away or are used up completely.

There is little remaining in the soil for following crops or plants. On the other hand, compost kickstarts an ongoing process that will continue indefinitely.

As noted above, not enough water can be an issue, but another disadvantage is when excess water is present, and the soil is free draining.

As the case dissolves, there is a window of opportunity to have the nutrients available in the rootzone before they are washed deeper into the soil profile and lost to the plant and the harvest.

This is important to understand, as overwatering can be both a financial loss and a crop loss in extreme cases. The home gardener is less exposed to this process, but the situation still exists.

This is the reason many home gardeners use the slow-release fertilizer.

Do fertilizers work in all soil types?

Fertilizer will not work in all soil types, however there are many soils where fertilizer is suitable, and soil pH and soil structure play major roles in suitability.

There are some soils where adding fertilizer can be toxic to your plants, and this is more likely to happen in temperate zones. Soils in temperate climates often have alkaline soils, meaning the pH reading is above 7.5.

The higher the reading the more risk. This problem can be seen in the wheat belts of Australia and is explained as Fertilizer Toxicity. There are two distinct versions of the problem, with one being salt toxicity or ammonia toxicity, and the other being ammonia toxicity.

The salt toxicity is problematic in drying soils and are not as sensitive to pH, whereas ammonia toxicity can be fatal to plants in alkaline soils. This issue is prevalent in urea-based fertilizer typically used in agriculture.

Can plants grow on fertilizer only?

There is a mountain of evidence to prove that plants can grow on fertilizer alone. This is just one part of the equation though. Growing does not equal healthy and natural.

What is not mentioned in many conversations is that growing plants on fertilizer alone can invite many problems and diseases to the garden or crop due to the lack of micronutrients and trace elements.

To address these problems and diseases, you just need to visit the gardening section of the local hardware or gardening center to recognize there is an entire industry feeding off these very same problems that have arrived at the gardener’s patch.

The crop farmer is in exactly the same situation but at an industrial scale.

Can using only fertilizers be harmful to gardens?

In some situations, only relying on fertilizer can be harmful to the plant or crop. Some/most fertilizer requires watering-in to release the minerals locked within. If the required water is not supplied or available, the plant can suffer chemical burn.

If the fertilizer application is too heavy the same can happen. This is why most fertilizer has a recommended rate of application printed on the packaging.

Compost does not have an application rate per se. It is most often applied when available, and you never seem to have enough.

How does compost work?

As noted at the beginning, compost is a natural product derived from a natural process. The key term here is natural.

Compost is the result of a biological process where garden materials are mixed with manures and scraps, and biology converts these materials into lower-form components closer to soil.

Compost, when ready for the garden, contains multitudes of beneficial bacteria and fungi that form connections with plants in the Rhizosphere, or the soil-plant interface.

These connections are part of a larger set of complex biochemical processes that are still being understood in scientific circles, with major implications for home gardeners who use compost.

Compost can be seen as an inoculation process rather than a fertilizer. While some nutrients are included in the compost mix, the true benefits are the biological partners we introduce into our soils and gardens.

We know compost works, and some of us get a bit nerdy with why it works.

What disadvantages does compost have?

As someone who regularly makes compost, I feel qualified to answer this appropriately. The disadvantages that we are aware of are mostly a result from actions by the gardener.

The primary disadvantage compost has is it requires care after creation. The life forms within the compost require protection to be able to do their thing for us in the garden.

A critical piece of information to remember is that compost is a living thing. There is an untold number of microscopic lifeforms within a teaspoon of compost, and they all require a home to be of benefit to us gardeners.

This means they need protection, and in the garden situation this means mulch. After applying compost to your garden bed, cover it with mulch. This allows the biology to relocate from the compost into the soil where they form the vital connections with your plants via the root system.

Without mulch to protect both them and the compost, they will die as they dry out and the whole exercise of making the compost is wasted. Some bacteria become dormant, and don’t die from being dry.

If you are serious about your soil, you may be interested in an opportunity to use mulch in partnership with compost to grow large quantities of certain plants. We accidentally stumbled onto a method where a particular mulch created the conditions for a huge ginger crop, and we wrote about it here.

The second compost disadvantage for us gardeners is there is never enough.

Does all compost have beneficial lifeforms?

There are instances where a compost heap can harbor problematic bacteria, however, the fix is a simple one. The unwitting gardener can apply compost containing these bacteria without knowing the risks, but a simple smell test can tell if the compost quality is questionable.

Healthy compost smells earthy and sweet. Poor compost stinks and is usually wet, sometimes soggy. It’s actually wrong to call it compost.

The problematic lifeforms are most often anaerobic, meaning they thrive in a low-to-no oxygen environment. This can be caused by not allowing air into the compost as it is progressing and making the compost too wet. The cure to the problem is oxygen and sunlight. The material (Still not compost) needs to be exposed to the sun and turned as it dries, and this kills any harmful bacteria that may be involved.

Once the material is dry and well aerated (Almost ready to be called compost again) it can be incorporated into a fresh pile to be composted correctly. The dead problematic bacteria will add to the nutrient load of the fresh compost pile, so nothing is wasted.

Can adding compost to a garden be considered fertilizing?

On some level, you could call compost fertilizer if we accept the meaning of the word “fertilizer” as “make fertile.” Adding compost to a garden will add fertility if the compost is well-made with diverse ingredients. Sometimes you can see a noticeable difference in the plants.

A poorly made basic compost can be looked at as a pimped-up version of mulch and will be of little fertility benefit, whereas a well made compost is an organic material that is teaming with life.

Compost could be considered a fertilizer if the entire process is taken into consideration. When you add compost to the soil, the benefits are just starting.

The lifeforms within the compost now enter the food chain in your garden and become the food source of higher forms of life. These include earthworms which are recognized as a symbol of fertility, ergo, fertilizing. By now you should be thinking about making your first compost pile.

Are animal manures considered to be fertilizers?

Animal manures can be considered a natural form of fertilizer. The type of animal it came from determines the strength and usage in the garden. Bird manures have greater amounts of phosphate, and cow manure has more nitrogen.

Each element is required in differing rates by individual plants and vegetables. It is recommended to age or compost all manure to limit the chance of over-application close to sensitive plants.

How does composted animal manure benefit gardeners?

The reason for adding animal manures to a compost pile is to extend the quantity of these bacteria so more of the garden can benefit. It’s basically a numbers game. A larger hot compost pile allows far more beneficial bacterial activity.

If there is a natural pathway to convert leaf and plant matter into fertilizer, this is it. Animal manures are like a middle ground between the manufactured chemical fertilizers and the hand-made compost product.

The nutrients in the plants the animal ate have been converted into plant-available nutrients within the animal’s gut via the bacteria living and dying.

These dead bacteria are then removed from the animal in what we call poop and are what feeds our plants if we apply the manure to the garden.

Some of these bacteria are still alive after being removed from the animal, and as they live off the grasses and leaves within the animal, they can continue to do the same outside the animal.

Most of the biology dies, but some continue to live, and these can thrive in a compost pile.

Are all animal manures the same?

The section above is pointed towards grass eaters primarily as they have the gut volume to hold vast numbers of bacteria. Bird manure holds phosphate in large quantities and is very beneficial to compost when added.

Can we make compost fertilizer?

Compost can be made to be equal or better than manufactured fertilizers. A gardener who is experienced in the compost process can harness the biological processes by using a calculated list of select ingredients in precise ratios.

The outcome can be considered a designer compost garden fertilizer that can rival the manufactured fertilizers. It is an enhanced version of compost that utilizes biology, biochemistry, and useful quantities of plant-available nutrients.

The process I am describing is adding biochar to the compost pile as it is made. There are many benefits to this material and are too many to list in this article. We think the benefits are so impressive that we wrote an article about compost for self-sufficient gardening you can access here, and it details adding biochar to homemade compost.

What is biochar?

Biochar is a material that is created by heating woody material in a low-oxygen environment in a dedicated chamber to drive out any volatile components that make up the wood.

The volatiles that are removed are then added to the external heating source to burn and generate more heat to further drive out more of the volatiles. The resulting material is chunks of pure carbon and is extremely useful.

Are there examples of biochar available to investigate and learn from?

The advent of the internet has allowed critical information to filter out to the individuals most likely to make use of that information, and a good example of this is something called Terra Preta. The term means dark earth or black soil, and it originates in the Amazon basin.

It dates back to the 1600’s and is a very fertile rich anthropological soil. The primary source of the dark color is thought to be carbon in the form of charcoal. It is also understood that the inhabitants of the time who had created the charcoal mixed it with human waste.

Over many years, potentially centuries, they were able to create vast areas of fertility not seen anywhere else. It can be considered a form of compost after the charcoal is added to the waste and left to age.

We know this charcoal as biochar in the modern world and adding this material to compost is where compost gets interesting.

Is organic fertilizer better than non-organic?

There is potential for confusion when shopping for the best fertilizer for your situation, and you may not be aware of the differences between these two versions of fertilizer. A brief description of both is below.

Organic fertilizers.

Quality organic fertilizers are designed to be a slow-release form of nutrients that are accessed through microbial activity. The more active your soil life is the more benefit the fertilizer will give your plants.

Because there is no salt casing around the fertilizer to harm the plant roots or build up in the soil, organic fertilizers are sympathetic to soil biology. Compost in partnership with organic fertilizer could be the perfect gardening partnership if you think about it.

Non-organic fertilizers.

The non-organic form of fertilizer is soluble as discussed above and is a one-time opportunity for the plant to utilize the nutrients. It is all available at once and is a “use it or lose it” proposition.

The risk for gardeners who use salt-based fertilizer extensively is loss of soil function over time and this will present itself through plant disease.

It is up to the gardener what path to take, but for the record, we only use organic versions of things and make our compost on site.


Compost versus fertilizer.

The difference between compost and fertilizer is stark when some information is digested. They both have a place, and it is up to the gardener to decide which is appropriate for each situation.

We use homemade compost and the occasional bag of organic fertilizer in certain locations in our system. We trust that you found the information useful and thank you for dropping by.

Article by Tim Blanch for He is a qualified Permaculture designer.