Compost vs. Fertilizer, Explained

Compost vs. Fertilizer, Explained

compost and garden fertilizer

by Matt Gibson and Erin Marissa Russell

Compost or fertilizer? What’s the difference? Which one should you be using in your yard or garden? Or should you use both? Everyone who is interested in growing their own plants wants to create a healthy garden environment. To keep plants growing as vigorously as possible, many gardeners consider using compost and fertilizer. Compost is an all-natural organic material to improve the quality and tilth of your soil, while fertilizer can be either organic or chemical, and contains specific elements in exact ratios that plants can use to grow. We’ll explain this in detail.

Experienced gardeners have no problem deciding whether they will use compost, fertilizer, or both in their gardens. Meanwhile, those of us that are new to gardening may have a little bit more trouble deciding what to use to keep their garden producing at a high level.

In this article we will break down what
compost is and what fertilizer is, respectively. We will break down the
commonalities and differences between the two soil additives, and we also
discuss the advantages and disadvantages of each.

What Is Compost?

Compost is basically a mixture of decaying natural substances, such as animals, vegetables, fruits, leaves, eggshells, coffee grounds and grasses. The decaying substances are then added into the soil to make the soil fertile and to boost the soil with lots of nutritional elements that plants need to grow and function at their best. Compost and other soil amendments are not rated with NPK (like fertilizer). With compost, you are generally trying to make your soil better and healthier overall by adding rich, organic material that improves the overall health and tilth of the soil.

Compost is just one of many soil amendments
that alter the soil to improve its physical or chemical properties. Other soil
amendments include lime, manure, leaf mold, ground bark, fertilizers, materials
to change water retention levels, clay, gypsum, and more.

Benefits of Compost

The advantages of using compost are as

  • Works as a good food for the entire
  • Keeps the natural health of the
    soil at high levels
  • Helps for the proper growth of
    beneficial microbes
  • Provides the soil with sufficient
    nutritional elements
  • Helps the soil retain moisture
  • Promotes proper growth of plants
  • Helps the soil fight against
  • Helps to control and limit weeds
  • Works to feed soil directly
  • Because you can make your own
    compost, it is much cheaper and environmentally friendly than fertilizer.

Compost sounds like a winner for multiple
reasons, but using compost in your garden also has its drawbacks.

Disadvantages of Using

The disadvantages of using compost are as

  • When using compost, you need to
    make sure that none of your garden plants have soil-borne pathogens
  • Compost takes more time to create
    an effect in the soil
  • Making compost can be a very
    time-consuming process
  • Making compost requires more
    physical labor than most fertilizers
  • As compost is made from decaying
    organic matter, sometimes compost spreads can be kind of smelly.
  • Compost takes more space to store
    and process.
  • An advantage to

What Is Fertilizer?

Fertilizer comes in organic and inorganic forms. Organic fertilizers, like manure, compost, or bone meal, are derived strictly from plant and animal sources. Inorganic fertilizers are made from minerals, gasses, and inorganic waste materials. Fertilizers made from organic sources feed and enrich the soil. Inorganic, or synthetic fertilizers are fast acting, but can burn and damage plants. 

All fertilizers are required by law to use the
NPK ratio system to measure the levels of Nitrogen, Phosphorus, and Potassium
(K on periodic chart) within them. So a fertilizer that is rated 12/12/12 has a
balanced amount of each nutrient within it. Your soil or plants might be in
need of one of the items versus the others, so you can choose a fertilizer
based on what you need. If you’re growing something that needs a lot of
nitrogen, you’d want one with a high ratio of it. 

Advantages of Using

The advantages of using fertilizer in the
garden are as follows:

  • Helps plants grow faster
  • Adds nutritional elements to the
  • Ensures the fastest growth of
  • Helps eliminate certain soil
  • Fulfills the specific needs of a
    wide range of plants
  • Provides macro and micro-nutrients
  • Provides essential nutrients that
    every soil needs, including nitrogen, phosphorus, potassium, and magnesium 

Disadvantages of Using

There are many more disadvantages to using
fertilizer in the soil than there are disadvantages of using compost. The
disadvantages of using fertilizer are as follows:

  • There is a risk of overloading the
    soil with nutrients when using fertilizer
  • Can cause severe environmental
  • Can pollute groundwater
  • Certain fertilizers can upset the
    symbiotic relationship of microbes in the soil
  • Fertilizers can break the
    microbial balance in the soil
  • Certain fertilizers are harmful to
    the environment as well as the human body
  • Fertilizers can be more expensive
    to use than compost, which is often made from food trash, leftover leaves, and
    kitchen scraps. 

Common Traits of Compost and

Compost and fertilizers can work together
really well when used properly. The organic matter in compost sponges up
nutrients within fertilizer and stores them until they are needed by plants.
Compost also provides many nutrients that plants need in very small amounts,
like boron. You can use fertilizer without using compost buy why miss a chance
to increase soil fertility and your soil’s ability to hold moisture. Soil that
is amended regularly with compost becomes rich, dark, and crumbly, often
needing much less fertilizer than soil that hasn’t been regularly treated with

Differences Between Compost
and Fertilizer

The easiest way to tell the difference between
compost and fertilizer is that compost feeds the soil while fertilizer feeds
the plants. Fertilizer adds to the soil’s nutrient levels. But instead of
feeding the soil food web, the ingredients in fertilizers are intended to meet
the needs of fast-growing plants. Sometimes the amount of compost gardeners are
directed to add to the soil is very general, fertilizer application rates are
based on the needs of plants. Either organic or conventional fertilizers work
well for veggies, but organic fertilizers have been shown to be better for
balancing the soil food web. Chemical fertilizer can also feed composting, but
continual use may throw off your soil’s chemistry and discourage beneficial
insects and microbes.

Common Questions and Answers
About Compost and Fertilizer

Are eggshells good for

You can add crushed or whole eggplants to your
compost pile to increase the calcium in the finished compost. Crushing the
eggshells before adding them to the pile will help them break down into the
compost more quickly.

Can I put bread in

Stale or moldy bread can be torn into small
pieces and added to your compost pile. Be sure to turn the pile or mix the
bread into it carefully after adding the pieces of bread to avoid attracting
rats, mice, and other pests to your compost pile. Some types of bread count as
green compost material (adding nitrogen to compost) and some count as brown
compost material (adding carbon to compost)..

Can I put compost in
potted plants?

You can add compost to your potted plants, but they don’t need much, and they don’t need it frequently. Add about an inch of compost to the top of the surface of your potted plants’ soil twice a year for best results. The same rule applies to using compost in window boxes. You can also make a potting soil out of two parts screened compost to one part sand or perlite.

Can I put moldy fruit
in my compost?

Yes, you can use moldy fruit in compost as
long as you meet a few conditions. Put the moldy food in the center of the pile
on top of dry brown material (like sawdust, ashes, straw, or leaves). The
reason the position matters is that the center of your compost pile gets hot
quicker and stays hot longer than the rest of the pile. Cover the food with
material like grass clippings, cornstalks, or shredded paper. Mix the fruit
well into the pile by turning it frequently so pests aren’t attracted to food
sitting on top of the compost pile.

Can I put potting soil
in my compost?

Many gardeners don’t realize that plants use
up the nutrients in potting soil after just one year of container gardening.
However, you can add last year’s potting soil from your containers to your
compost pile. Keep in mind that the bits of perlite in your potting soil won’t
break down in the compost pile.

Can I put tomatoes in
my compost?

If for some reason you don’t want to eat your
tomatoes, you can add them to your compost pile. That said, be advised that the
seeds inside the tomatoes may sprout next spring inside the pile or wherever
the compost is placed. If this happens, you can pull them like weeds or
transplant the tomato plants to the right part of your garden. Please note that
if your tomatoes have contagious plant diseases, you should only add them to a
hot compost pile. If your compost isn’t hot, burn or bury the diseased

Can too much compost
hurt plants?

Although it’s possible to get too much compost
in your garden soil, resulting in an overload of certain nutrients that’s bad
for plants, this doesn’t usually happen. If you’re worried, though, limit
yourself to one or two inches per foot of loosened soil when you’re planting a
new bed and half an inch to an inch each fall on top of existing beds.

Can onions go in

Cooked and raw onions can be used in compost
piles. The only exclusion is onions that have soaked up lots of fatty or meaty
juices, which shouldn’t be used because they can attract pests to your compost
pile. If you’re adding in raw onions, you may wish to chop them into halves or
quarters to discourage the onions sprouting into new plants. It also takes a
good bit of moisture to start breaking down a whole raw onion, so mix these
well into the center of your compost pile.

Can orange peels go in

Unless your composting approach is vermicomposting, orange peels are an excellent addition to your compost pile. The orange peels will add phosphorus, nitrogen, and potassium to the completed compost. To reduce the amount of time it takes for orange peels to break down, you may wish to break them into small pieces before adding them to your compost heap.

Can you fill a raised
bed with just compost?

It’s not a good idea to fill a raised bed or
any are of your garden completely with compost. The best approach is for your
garden’s soil to consist of five percent organic material. As a rule of thumb,
you can add one or two inches of compost per foot of loosened soil when you’re
creating new beds, or in the fall, you can spread half an inch to an inch of
compost on top of existing beds.

Can you keep adding to
a compost pile?

Yes, you can keep adding to your compost pile
whenever you have new scraps that will work for it. This style of composting is
called cold or passive composting. This type of composting takes a while to see
results. You may need to wait between three and eight months before you have
completed compost you can use. Start with about three inches of moistened
coarse, strawlike material, like plant stems, leaves, twigs, hay, or straw, and
do your best to add brown materials on top of green materials. Your finished
compost that’s ready to use will be available from the bottom of the bin or
pile once it’s ready.

Can you mix compost and

You may add horse, cow, sheep, rabbit, or
chicken manure to your compost mixture, and doing so actually reduces the risk
of burning plants with fresh, unadulterated manure. Do not use manure from humans,
dogs, or cats in composting. Composted manure may be used as a mulch for plants
once it’s had time in the heap, bin, or pile to break down. Another option is
to till manure into the soil long before spring planting, like in the fall or
winter, so it has time to break down. Adding manure to your garden’s soil helps
loosen too-firm, compacted dirt and adds moisture to sandy soils. Manure also
increases the carbon and nitrogen available for your plants in the soil as well
as lowering the risk of runoff or leaching nitrates from the soil.

Can you put banana
peels in compost?

Banana peels are an excellent addition to
compost. In addition to breaking down quickly, they’re full of nutrients to add
to your soil, such as calcium, magnesium, phosphates, potassium, sodium, and
sulphur. If you want your banana peels to break down even quicker, you can cut
them into small pieces.

Can you put dead plants
in compost?

All kinds of plant material is suitable for
composting, including cut grass, leaves, weeds and other gardening trash, straw
or hay, and dead plants. Only include debris from plants with contagious
diseases if you use hot composting. Otherwise, this material should be burned
or buried. Plant materials you should not compost include seed-containing
invasive weeds, branches, wood chunks, and anything overly soggy.

Can you use too much
organic fertilizer?

Yes, it’s possible for your plants to overdose
on fertilizer, even when it’s organic. The results of getting too much
fertilizer include burned roots, yellowing leaves, “leggy” or spindly growth,
lots of foliage but no fruiting, and increased risk of pests and disease. For
best results, follow the instructions provided by your fertilizer’s
manufacturer, or you might decide to add fertilizer before the spring growing
season begins to reduce the risk of burning your plants.

Do you need to
fertilize if you use compost?

Whether you’ll need to use fertilizer along with your compost depends on what you’re growing and what your soil is like. The best way to know whether your soil will be able to provide the nutrients your plants need to thrive with a boost from compost now and then or whether additional fertilizer is needed is to do a soil test. Most of the time, these are available through your local Extension office, which you can find by choosing your state from this map on the National Pesticide Information Center website.

Does compost need

You can set your compost pile, heap, or bin up
either in the sun or in the shade, but be aware that letting your compost get
plenty of sunlight will speed up the decomposition process. As the temperature
increases, so does the activity of the bacteria and fungi in the compost. If
you choose a location in full sun, you may need to moisten your compost heap

How do I add compost to
my garden?

To avoid adding too much compost to your
garden at a time, follow this rule of thumb. For new garden beds, add one or
two inches of compost per foot of loosened soil. For existing garden beds, add
half an inch to an inch of compost in the fall.

How do I apply
fertilizer to my garden?

For results specific to your fertilizer, you
should follow the directions provided by the fertilizer manufacturer that are
printed on the package. Most balanced fertilizers are added every three or four
weeks during the growing season. Organic soils may require increased
fertilizer, and clay soils may need fertilizer less often, like every four to
six weeks. Because there are so many different types of fertilizer, make sure
to check the instructions for dosage and application for the type you’re using.

How do you know when
compost is ready?

You can tell when your compost is ready just
by looking at it, smelling it, and touching it. When your compost looks like
fertile, dark soil instead of a bunch of rotting food scraps, it’s ready to
use. You won’t be able to recognize the ingredients making up the compost when
it’s finished, and finished hot compost doesn’t heat up, even when it’s mixed.
Compost that’s ready to use should not feel slimy to the touch. Depending on
the style of composting you’re using, it will take anywhere from one month to
two years to create finished compost. Allowing a few months after your compost
looks done for it to “cure” helps ensure it’s chemically stable.

How do you mix compost
into soil?

If you’re digging in an area to start a new
garden bed, you can add one or two inches of compost per foot of loosened soil.
For existing garden beds, spread half an inch to an inch of compost over the
bed in the fall.

How long can you keep

You can keep compost if you intend to use it
the following season. Holding onto your finished compost for longer than that
can result in lowered nutrition in the compost. To store your compost, you can
cover the pile or heap with a tarp or put the finished compost into trash cans
with lids or plastic bags. If you choose plastic bags or trash cans, open them
up periodically to give things a stir and check moisture levels. The bottom
will be damper than the top, so pull that bottom layer up to keep things

How long does it take
for compost to turn into soil?

Depending on the type of composting you’re
doing, it can take anywhere from one month to two years for the compost to be
complete and ready to use. You know your compost is ready when it looks,
smells, and feels like dark, fertile soil. You won’t be able to recognize its
ingredients, and if you use hot compost, it will stop heating even when it’s
mixed. Allow it to rest and to cure for a few months after this point to make
sure it’s chemically stable. You can speed up the composting process by
limiting your pile to one cubic yard, turning the materials once a week, and
keeping your ratio of carbon to nitrogen around 20 to one. Keeping the pile
moist and shredding or chopping the materials you add to your compost also
makes things decompose faster.

How long does it take
for organic fertilizer to work?

It will take microorganisms in the soil
between two and six weeks (depending on soil temperature and moisture level) to
break down organic fertilizers so the nutrients they hold are available for
your plants. To ensure you’re using your fertilizer correctly, follow the
instructions the manufacturer has provided. They’re usually printed on the box
for your convenience.

How long should
fertilizer be down before it rains?

Let your fertilizer rest on the soil for two days
before there’s any rain forecasted. Rain before this time can wash the
fertilizer away before it has a chance to become part of your soil. Also, if it
rains right after you’ve applied fertilizer, your fertilizer may start running
off into nearby lakes, rivers, and streams. This disrupts the nearby ecosystem
and reduces available oxygen in the water.

How much fertilizer do
I need?

To make sure you don’t give your plants too
much or too little fertilizer, rely on the instructions provided by the
manufacturer that should be printed on the package.

How often should I turn
my compost pile?

Turn an active, hot compost pile every three
days until the compost stops heating up. Failure to heat even when mixed is a
sign that tells you the compost is almost ready. (Just give it a couple more
weeks to cure.) If you don’t use hot compost, you can scale back to turning
your compost once per week.

Is compost a fertilizer
or soil amendment?

A soil amendment is anything you add to your
garden soil to increase its quality and make it better suited for gardening.
Examples of soil amendments include peat moss, wood chips, straw, manure, grass
clippings, gypsum, wood ash, vermiculite, and perlite. Sometimes, the amendment
you need to use for your soil might be fertilizer. A fertilizer is anything
that provides the plants you grow with the nutrients they need to thrive,
including compost. That means that compost is both a fertilizer and a soil

Is compost good for all

Compost benefits all kinds of plants, as long
as you don’t give them too much. A good rule of thumb is to use one or two
inches per foot of loosened soil when you’re digging new garden beds and half
an inch to one inch over existing beds in the fall.

Should I add worms to
my compost?

There’s no need for you to add worms to your compost area, though it won’t hurt to throw them in. Most of the time, the worms in your yard will find your compost pile on their own. The exception to this rule is vermicomposting, which uses lots of worms that you’ll need to manage and care for yourself.

Should I water plants
before fertilizing?

Granular fertilizers should be followed with
plenty of water to prevent burning your plants. Of course, water-soluble
fertilizers are applied while you water your plants. There is no need to water
plants before fertilizing unless recommended by your fertilizer manufacturer.

Should you mix compost
with soil?

For best results, your garden soil should be
made up of about five percent compost. You can either mix the compost into the
soil or apply it on top like you would mulch. A good rule is to apply one or
two inches per foot of loosened dirt to the top of a new garden bed and half an
inch to one inch over existing beds each fall.

What foods cannot be

Foods you should not compost include meat,
skin, bones, dairy products, greasy and fatty or spicy foods, sweets, salad
with dressing. Unless your style is hot composting, you should also not include
gardening debris or plant matter that has a contagious disease. Instead, burn
or bury this trash. Non-food items that you should not place into your compost
pile include human or pet manure, branches and wood chunks, coal fire ash,
sawdust from treated wood, tea or coffee bags (grounds or leaves are OK),
invasive weeds that have gone to seed, lots of soggy material, plastic, metal,
glass, glossy or coated paper, wood ashes, lime, stickers/labels on produce,
BBQ charcoal, synthetic fertilizer, and anything too heavy to decompose, like
heavy cardboard.

What is the ratio of
compost to soil?

The ratio of compost to soil varies depending
on what you’re growing. For potted plants, use a mix that’s 20 to 50 percent
compost. A vegetable garden, however, just needs one or two inches per foot of
loosened earth for a new bed or, for existing beds, half an inch to an inch
each fall.

When should fertilizer
be applied to plants?

For instructions specific to the type of fertilizer you’re using, check the packaging for guidelines from the manufacturer. Different types of fertilizers will have different dosages and application instructions as well as schedules for application.

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