Compost vs. Peat Moss: When Do You Use Each One?

Compost vs. Peat Moss: When Do You Use Each One?

differences between compost and peat moss

by Matt Gibson and Erin Marissa Russell

Peat moss and compost are two all-natural soil
amendments that are commonly used by modern gardeners to adjust the physical
structure of the soil and to help improve fertility and increase nutrient
levels. Each of these soil amendments has different properties and should be
used when there is a specific need for the ingredients while creating a balance
in your property’s soil and rejuvenating it for upcoming growing seasons.

Though compost is widely available
commercially, many gardeners around the world process and create their own
compost by recycling garden, lawn, and kitchen scraps and allowing them to
decompose in a controlled environment. Peat moss, on the other hand, is mined
from bogs in Canada and in the northern US using surface harvesting. Organic
gardeners use a variety of different soil amendments to help them get the most
out of their soil. Read on to learn more about compost and peat moss.

Improving Your Soil Quality

In order to improve the quality of your soil,
you need to understand what you are working with. Soil building and soil
enhancement are important tasks that help you improve your soil, but you need
to know what your soil is lacking before you can choose the correct amendments
that you want to use to balance and reinvigorate your soil.

The best way to figure out what kind of soil
that you have is to have the soil tested by your local extension service or by
a company that offers soil testing services. Alternatively, you can purchase a
home soil test kit and test it yourself. After you know your soil’s salinity
and pH level, you will have a better idea of which amendments you will need to
add to balance your soil to optimal levels for the upcoming growing season and
beyond. Most labs will also provide recommendations on what amendments to use
to and what quantities of each are needed to help balance out your soil
efficiently. 

Differences Between Compost and
Peat Moss

Compost is relatively cheap to purchase and
it’s also free to make your own using kitchen and garden scraps, though it does
take some time to decompose and mature. Compost is cheaper than peat moss, as
peat must be harvested, packaged, and transported. Peat’s composition is pretty
consistent and uniform, whereas compost is composed of many different sources,
including leaves, kitchen scraps, wood, decaying plant matter, and more, so it
varies in quality more so than peat moss. 

Compost that is made mostly from plant
products tends to be low in salt, but salinity levels can vary in compost
depending on what the compost is made from. Peat moss, on the other hand, is
very low in salt content and is often used to reduce salt levels in garden
soils. Compost pH is usually neutral or alkaline, while peat moss pH levels are
quite acidic, usually in the range of 4.4 When large amounts of peat moss are
added to your soil, lime should also be mixed in to help neutralize the pH
level.

Compost is rich in nutrients, contains many
helpful microorganisms, and can be an excellent mulch when added as a top layer
to your garden beds. Peat moss is not incredibly fertile but it does have some
nutrients and microorganisms. Peat moss is not a good mulch as it has such a
high water retention that it can keep water from passing to the soil below.
Also, when it dries out, it can simply blow away in the wind.

Compost can compact and sometimes contains
weed seeds, unlike peat. Because peat moss does not compact, it can provide
excellent soil aeration for multiple years. Both compost and peat moss hold
water well, but peat moss has better moisture retention levels, especially when
added to rocky or sandy soils.

All About Compost

Composting, as a gardening technique, has been
around for centuries. Adding decomposing organic matter to your soil is the
most natural way to replenish nutrients and fertilize the topsoil and beyond.
Because it takes multiple years for topsoil to naturally replenish itself,
gardeners and farmers have used compost instinctually to assist the
replenishment process to help the soil produce valuable crops year after year.

These days, composting options have a
repackaged modern appeal. Homes, corporations, small businesses, and
communities have worked together to create regular composting systems.
Composting bins are available everywhere you look thanks to the efforts of environmental
activists and their composting awareness campaigns.

Home composting systems only require a
small bin or container in the kitchen area where food scraps are collected.
It’s always a good idea to break down your kitchen scraps as much as possible by
chopping or shredding them before dumping them into the container.

Add a thin layer of soil and a small
amount of water to the mixture intermittently to help speed up the
decomposition process. Don’t add too much water at one time, however, as
compost materials do not have the ability to absorb much water at once, so it
is essential that water is added slowly over the period of several weeks.
Otherwise, the whole mixture may likely turn into a gross, stinky mush. Keep in
mind that the process of decomposition produces its own liquids as well, so it
doesn’t take much water to keep the bin moist, but not watery. If the mixture
starts to become too soggy, add more scraps and soil to balance it out.

Composting in a contained environment is
very different from composting methods of old. Original composting was simple.
Farmers just threw out their potato peelings and other scraps into the garden
and let their pigs do the rest. The pigs would eat the scraps, digest them, and
then spread the manure over their crop fields.

Though the methods of today’s composting
and the composting of the past vary greatly, the end result is pretty much the
same. Nutrients are processed and transferred from decaying organic matter into
usable garden soil. When the soil is fully fertilized, it is believed to have
absorbed the full potential of nitrogen and other essential nutrients found in
healthy soil.

Uses For Compost

Commonly called black gold, compost uses a
process known as cation exchange capacity to improve the structure of the soil
and help it to better hold nutrients. Compost also promotes the presence of
earthworms which significantly improve the soil quality. Earthworms enrich the
soil by digesting and processing decomposing organic matter and producing
nutrient-rich castings, as well as helping the aeration of the soil by
burrowing through it.

Compost can be used as a backfill when
planting shrubs, trees, and perennials. It is perfect for establishing planting
beds and lawns. It can also serve well as a mulch for landscape plantings and
gardens, and as a side dressing for vegetables or for erosion control.

All About Peat Moss

Peat moss is a decomposed fibrous material
which forms when mosses and other living materials decompose within peat bogs.
The most important difference between peat moss and the compost that garders
create in compost bins in the backyard is that peat moss is composed primarily
of moss, and the decomposition occurs without the presence of air, which
significantly slows the process of decomposition. While you can create quality
compost in less than a year’s time, it can take several millennia for peat moss
to form. Peat bogs gain less than a millimeter in depth every year. As the
growth rate of peat moss is so slow, peat moss isn’t considered to be a
renewable resource.

The majority of the peat moss that is used in
the United States comes from bogs in Canada. Even though the mining of peat moss
is strictly regulated, groups like the International Peat Society highlight the
significant controversy surrounding peat moss harvesting. While only 0.02
percent of the reserves are available for harvest, the mining process releases
massive amounts of carbon into the atmosphere, and the bogs continue to spill
out excess carbon long after the mining is completed.

Because of the environmental concerns, many
gardeners feel guilty about using peat moss in their gardening projects. People
with strong feelings on either side of the issue each can make a strong case on
the ethics of using peat moss in the garden, but in the end, it’s up to you to
decide whether the environmental effects overpower the benefits to your garden
that peat moss provides. As a compromise, perhaps consider using peat moss as
sparingly as possible in garden projects, using it only on a case-by-case
basis, for projects such as starting seeds or making your own potting mix. For
larger projects, such as amending garden soil, use compost instead.

In the garden, peat moss is a great choice as
a growth starter for plants, fruits, flowers, and vegetables and it meets
organic farming requirements as well. Peat moss is commonly used as a soilless
alternative for starting seedlings in a greenhouse setting due to its ability
to retain moisture for lengthy periods of time. Peat moss is also widely used
as an alternative for household plants because of the safety of the ingredient
mix and its ability to retain water for long periods. It is able to absorb
water quickly and store it efficiently until it is needed.

In regions that receive large amounts of
rainwater, peat moss is an ideal candidate for outdoor use. It works well for
household gardening as well because plants can be watered just once per week,
or often even less if a fair amount of water is given with each watering.

The majority of peat moss mixes are made from
a base of decomposed sphagnum moss. This base is often mixed with other organic
materials and other mosses and then blended together and sifted prior to
packaging and selling. Peat moss ranges in texture from rough, resembling
clumpy dirt, to a medium similar to chopped up tree bark.

Peat moss smells like organic matter, but is
no more pungent than a compost bin with the lid removed. It’s safe for indoor
and outdoor use and is not toxic to humans, animals, or the environment. Peat
moss is ready to use fresh from the package, unlike composting materials, which
can take months to be ready to use in your garden beds.

Uses For Peat Moss

Peat moss is most commonly used as a soil
amendment. It is also often used as an ingredient in planting mixes and potting
soils. Some gardeners even add peat moss to their compost as a carbon source,
as well as a bulking agent. As peat moss is sterile, its presence in soils can
help minimize disease issues. Peat moss should never be used as a mulch because
it can blow away in the wind if it becomes dry and its fibrous structure and
water retention capability can steal moisture from the underlying soil.

Home gardeners use peat moss as a soil
amendment or as an ingredient in potting soil. Its acidic pH level makes it
perfect for acid loving plants such as camellias and blueberries. For plants
that like a more alkaline soil, compost is a much better option. As peat moss
doesn’t break down readily or compact, just one application can last for
several years before needing to be replaced. Peat also doesn’t contain harmful
microorganisms or pesky weed seeds that may be present in poorly made compost.

In smaller amounts, peat moss is an important
component of most store-bought potting soils and seed starting mediums as it
holds several times its weight in moisture and releases the water to the plants
roots as its needed. Unlike other mediums which allow nutrients to be leached
out of the soil with rain or irrigation, peat moss holds onto nutrients so that
they are not rinsed out of the soil with ease. Peat moss, by itself, does not
make a good potting medium, but must be mixed with other ingredients. Potting
soils should be comprised of one third to two thirds peat moss at most.

Oftentimes, peat moss is referred to as
sphagnum peat moss as much of the decomposed material in a peat bog comes from
sphagnum moss which commonly grows on the top of the bog. Sphagnum moss and
sphagnum peat moss, however, are two distinctly different materials. Sphagnum
moss is comprised of long, fibrous strands of plant material, and is often used
by florists to line the insides of wire baskets, or as a decorative filler for
potted plant compositions.

Compost Vs. Peat Moss

Compost and peat moss are both common soil
amendments that are each added to soils to improve them in different ways. When
deciding which ingredient to add to your garden beds, here are some important
differences to consider.

Peat moss is a bit more expensive than
compost, especially if you are making your own compost, or purchasing it from a
local source. Compost can also be cheaper when purchased in bulk. The peat moss
that we buy is generally sourced from Canada, so harvests must be shipped from
there, which increases the cost exponentially.

If nutrient content is what you are after,
peat moss has very little to offer in that regard. Compost is much better for
replenishing nutrients in your soil. However, compost is not an alternative to
fertilizer. Fertilizer is much higher in nutrient content than compost, and
will still be needed no matter what soil amendments you use to help keep
nutrient levels high enough to allow your plants to thrive.

The main nutritional value that comes from
using compost is from its effect on soils and the microorganisms that are
contained within the soil. Peat moss increases the cation exchange capacity of
the soil, helping it to hold on to nutrients for extended periods, like
moisture, releasing them when needed to help your plants thrive. 

Peat moss has a low pH (4.4), so if you use a
lot of it, lime should be added as well to balance out the acidity. Plants that
thrive in acidic soils (called ericaceous plants) such as blueberries and
rhododendrons, love growing in peat, but most plants tend to prefer soils that
are closer to neutral in pH range. Compost typically has a neutral pH level or
slightly alkaline leaning.

Peat moss can last for years in soils, as it
doesn’t compact and provides ample aeration and water retention. Compost has a
tendency to compact, as well as lose its nutritional value over time, so it
should be replenished on a yearly basis. Both mediums hold water, though peat
moss tends to hold water more efficiently. This makes it a great choice for
amending sandy or rocky soils that tend to lose moisture, as well as nutrients,
too quickly.

Peat moss can be hard to get wet at first, and
once it dries out, it can be very hard to re-wet. Composts tend to vary
depending on the contents of the compost mix, on how easy they are to re-wet.
Once wet, both these materials hold water very well and release it to the roots
of your plants over time. If peat moss gets too dry, you can moisten it in a
plastic bag overnight. Using warm water will help speed up the process, as it
is absorbed much easier and quicker than cold water. You can also add a few drops
of detergent to the water to act as a surfactant, which will help speed up the
re-wetting process.

Composts have many variables in their
composition, which depend on the sources used to create the compost. Peat moss,
on the other hand, has a uniform composition. Composts may also contain some
contaminants, depending on source materials. Peat moss contains very few
microorganisms, while composts are rich in microorganisms. More often than not,
these microorganisms are beneficial, and can improve the soil drastically, by
helping to aerate it and by replenishing nutrient levels.  

Peat moss contains no weed seeds. Composts
which are prepared properly should not contain weed seeds, but this is not
always the case. If the compost was treated well, it would reach high enough
temperatures to kill any weed seeds during the decomposition process. If it
remained properly covered during the preparation, that would prevent any weed
seeds from blowing in. Sometimes, however, inexperienced gardeners may compost
weedy plants, which could lead to contamination of weed seeds. To test out your
compost, put some into a pot and water it. After a couple of weeks, you should
be able to tell if any weeds have begun to germinate. It’s a good idea to test
out compost before adding it to your garden beds to make sure you are not
growing weeds instead of your desired plants.

Peat moss contains no disease suppressing
qualities, compost, on the other hand, contains microorganisms, which may
suppress some disease-causing pathogens. Peat moss is a natural resource,
obtained by harvesting peat bogs. Peat moss is usually obtained from surface
harvesting. Due to modern environmental regulations, most of this is done after
conducting environmental impact analysis research, which has led to more
renewable and sustainable harvesting techniques. Composts, alternatively,
nearly always use recycled organic matter. 

Peat moss should never be used as a mulch,
while composts are great for using as a mulch or side-dressing around garden
plants. The only downside to using compost as mulch is that unless it is
applied in thick layers, composts won’t suppress many perennial weeds. Peat
moss should never be used as mulch as it will dry out soils by absorbing water
from them, not allowing it to penetrate beneath the mulch layer. Also, once
dry, it may blow off the surface.

A solution to the differences between peat
moss and compost is to use both in combination in order to reap the benefits of
each medium. Some gardeners incorporate peat moss and compost when planting,
then top dress perennial plants with compost in subsequent years. Peat moss
decreases the tendency of compost to compact, which may extend the life of
compost dramatically.

Alternatives and Combinations

Peat moss and compost, when used in
combination, have shown very positive results for many gardeners attempting to
enrich their soils. Using a combination of the two amendments provides
gardeners with a way to reap the benefits of both products. 

In addition to compost and peat moss,
there are many other methods for treating and amending soil in the hopes of
providing a better medium to increase plant productivity. Aside from other soil
amendments, there are alternative methods to replenishing healthy soil. Some experienced
farmers and gardeners use the fallow field theory, giving their land, or garden
beds, a periodic rest, typically once every seven years, to allow the land to
naturally replenish itself. The idea behind this theory is that the ground
knows how to heal itself and needs to give, as well as receive. By allowing
your land to rest occasionally, instead of placing a consistent demand on your
soil, you allow the land to heal and renew itself for future harvests. 

By choosing to not plant in a particular
area for a year, gardeners and farmers allow the land time to regenerate
nutrient levels. During the fallow year, farmers and gardeners can also apply
treatments such as soil amendments, fertilizers, and other additives, to give
their crops a boost for the next planting season by enriching their topsoil.

Field or soil aeration is another popular
method for treating and improving your fields or garden beds. Using a mini
tiller, you can turn the topsoil over in rows, bringing to the surface a
healthy layer of soil with unused nutrients. The used layer of soil is turned
underneath the top layer, where it can begin to regenerate while not disturbing
the new plants.

Which is Better?

After a review of the information provided in
this article, you should be able to better make the right decision for amending
your soil using compost, peat moss, or a combination of the two, when needed.
The compost versus peat moss debate is only one of the concerns you may face
when willing your crops to grow into plentiful harvests. Compost is better for
certain tasks and peat moss is better for others. Amending your soil is all
about balance and knowing what your soil is lacking beforehand.

Common Questions and Answers About
Compost Versus Peat Moss

Are peat moss and compost the
same thing?

Peat moss and compost are not the same thing.
Peat moss is a natural product that’s formed as layers of moss grow over one
another. (Peat moss is the bottom layer.) Compost is made as everyday waste
materials decompose into nutrient-rich soil. Peat moss is sterile, has an
acidic pH, and is not high in nutrients or microorganisms. Compost is high in
both nutrients and microorganisms and has either a neutral or slightly alkaline
pH.

Does peat moss loosen soil?

Adding peat moss to heavy or compacted soil is
a good way to loosen and aerate it for gardening. Peat moss also improves
soil’s ability to drain well, and in sandy soils, adding peat moss helps the
soil retain water and make moisture available to plants.

Does peat moss make good compost?

You can use peat moss when setting up a new
compost pile or add it to an existing compost heap as a brown, or carbon,
material. It will help to balance out green materials that are heavy in
nitrogen. If you’re using peat moss to start a new compost pile, spread a layer
of eight inches of peat moss, then cover it with a few inches of soil from the
garden or finished compost. In existing compost piles, you can spread a layer
of peat moss over the pile when the bottom layers begin to decompose, then use
a fork or spade to mix the peat moss into the compost. If your compost heap has
begun to smell, that usually means the compost has too much nitrogen, and
balancing it out with carbon-rich peat moss will help keep the smell at bay.

Does peat moss make soil acidic?

Peat moss is rather acidic, with a pH level
that’s usually around 4.4. Most soils are much more alkaline than peat moss, so
adding peat moss to your soil will increase its acidity.

Does peat moss raise pH?

Because peat moss has a pH level around 4.4 and soil usually has a pH level between 4 and 8.5, most of the time adding peat moss to soil will raise the pH level, not lower it. If you aren’t sure of your soil’s pH level, refer to our article How to Test pH In Your Soil.

How does peat moss improve soil?

Peat moss improves soil because it does not
compact over time, so it loosens soil and aerates it. Adding peat moss to soil
also helps increase the soil’s capacity for drainage. In sandy soils,
incorporating peat moss will help the soil to retain water and make moisture
available for plants.

How long does it take for peat
moss to break down?

It takes several years for peat moss to break
down and decompose, making it a long-term amendment to your soil. Compare the
several years it takes for peat moss to decompose to the single year it takes
for compost to decompose.

How much compost do I add to clay
soil?

Add a layer of one or two inches of compost
over the area of clay soil you wish to amend, then mix the compost into the
soil. If you’re working with sandy soil instead of clay soil, use a layer of
three inches instead of one or two.

Should I mix peat moss with soil?

In almost all cases, peat moss should be mixed with soil before it’s used in gardening. Soak your peat moss in water before mixing it with soil to hydrate it. Let it soak for a few minutes, then stir and add more water.  Your peat moss is well hydrated when a drop or two of water comes out when you squeeze a handful. You do not want to add so much water that it streams out when squeezed. Then add a layer of two or three inches of peat moss over the area of soil you wish to amend. Mix the peat moss down into the top 12 inches of soil.

Want to learn more about compost versus peat moss?

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Garden Myths covers Compost Creates Acidic Soil

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Grow Organic covers How to Use Soil Amendments

Harvest to Table covers How to Improve Clay Soil

SFGate Homeguides covers How to Acidify Soil with Peat Moss

SFGate Homeguides covers How to Put Peat Moss in a Compost Pile

Peat and Peatlands covers Healthy Soil Makes a Healthy Garden

University of Vermont Extension covers Peat Moss of Compost?

Saving Water Partnership covers Compost and Mulch Calculator

Sunday Gardener covers Differences Between Peat Moss and Compost

The Garden of Oz covers The Perils of Peat Moss

compost hands holding peat moss with text overlay compost versus peat moss

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