Jan 19, 2022

How to Determine the Best Compost to Use

Gardeners talk about compost a lot, not only the compost itself, but the verb form as well – composting.  But how do you know what the best compost to use in your garden?  In the blog today I’ll give you some information about how purchased compost is made, what it’s good for, and why you’d want to use it.

But first, let’s define what compost is.

compost bins in the garden

Compost bins in the garden

What is Compost?

Compost (commercial compost) is a growing medium made of natural materials such as forest materials, bark, leaves, soil, and other components in our best attempts to recreate the natural balance of moisture, air and nutrients that most plants thrive in – an undisturbed forest floor. 

The composted forest floor naturally has layers and layers of leaves and other natural materials (wood, insects, even expired animals).  The top layer of leaves and other material that we see has just fallen recently.  The lowest layers of leaves and other material has degraded – rotted – into particles that provide nutrients to the trees that are producing the leaves.  And thus the cycle continues – forests feed themselves without help from mankind (and will do so long after we’re gone).

compost area

Purchasing (or making) compost attempts to recreate the last steps of complete degradation to feed the plants you are trying to grow.  The materials in compost make the tiny molecular connections to the live roots of plants via interactions with fungi and other microbes and create a symbiotic relationship – the plant feeds the soil organisms sugars it creates via photosynthesis, and the soil organisms process and offer up major and minor elemental nutrients to the plants as payment, as well as better access to water (again, at the molecular level).

You can purchase many different types of compost and growing mediums for different types of plants.  While nothing will be as fertile as undisturbed “virgin” lands, we can come pretty close.

Types of Compost

There are many types of compost.  We’ll go over a few here so you know what characteristics they have and how to apply those characteristics to what you’re trying to accomplish in the garden.

Loam-based Compost

Soil Texture Triangle

Think of this triangle in terms of weight of the particles of a soil sample as they’re suspended in a jar of water. After that soil sample is shaken up in the water and then allowed to settle, you’ll generally see striations. The top striations will be clay layers, the middle will be silt, and the lowest and heaviest will be sand. Organic materials usually float!

Loam-based compost is a sterilized growing medium made from loam – which is a soil with approximately equal portions of sand, silt, and then slightly less clay (about 40-40-20, respectively).  It is a relatively heavy compost, which is great for plants with a top-heavy structure, like trees.  Many have time-release fertilizers added, but you can purchase them without.

Your “top soils” and “garden soils” often have loam in them, and when you lift those bags you can tell by how heavy they are.  Composts that are loam-based have organic material mixed in, but in order to maintain that heaviness it’s a smaller proportion of organic material, which gives the compost some loft and “structure”.  Much of the organic material in Loam-based Compost is shredded tree bark, byproduct waste of paper and lumber industries.

Loam-based composts are usually best for amending lawns, top-dressing and/or adding volume to landscape soils, and cutting into other, lighter composts for raised beds and containers. 

Peat-based Compost

aerial view of a peat bog

This is an aerial view of a peat bog. It took thousands of years for the tiny layers of moss to build up these berms, where trees can now take root without rotting and feed on the nutrients in the waters of the bog.

Peat-based compost is either all peat (great for seed germination) or a mix of peat and sand/soil where the majority of the mix is peat. This gives the compost a very light and airy feel that is pleasant to handle.  Many plants thrive in peat-based compost and this makes them very popular at garden centers. 

When you lift a bag of peat-based compost, it is light and almost fluffy, and this is a good thing.  These composts are often tilled into native soils and raised beds to loosen compacted soils – such as the sandy soils of Florida and the clay soils of Georgia and Alabama.  They provide organic material to allow the development of healthy microbial colonies that help plants take in nutrients in the method that we discussed previously – creating symbiotic relationships with the organisms present in the soil. 

Many of these commercial composts have fertilizer added to them, but others do not, so read your labels carefully to determine which is which, if you are concerned about it one way or the other. 

One down-side to peat is that when it loses all moisture, it becomes hydrophobic and is very difficult to re-wet.  It also can be overwatered very easily and retain very large amounts of moisture, which can easily cause root rot.

Coir-based Compost

raw coconut coir

Raw coconut fibers from the husks of coconuts which coir is made from. It is a plentiful byproduct of coconut consumption and has been used as mulch for centuries in tropical parts of the world.

With the widespread depletion of the peat bogs of the world, and the fact that they take millennia to reform properly, many people have been looking for alternatives to peat.  Coir is made from the byproduct waste of coconut processing – the husks of the coconut are ground and actually make a wonderful substitute for peat in compost mixes. 

Coir has similar properties to peat, but we can grow a coconut tree much faster than a peat bog! Coir is thus more renewable than peat.  Coir doesn’t hold quite as much water as peat, either, so for plants that need more drainage, coir is a wonderful addition to soils to give it structure, loft and drainage too.

Coir has a similar behavior to peat for seed germination as well. In fact, coir pellets that expand when watered have been created for just that purpose – to create transplantable “easy plugs” for your seedlings to cut down on transplant shock. We have them here at Shell’s if you want to see them. 

Mushroom Compost

mushrooms growing in rich compost material

Closeup of a “chunk” of mushroom compost that edible mushrooms are grown in. It contains lots of great organic material like rotting wood and fungi-rich soil. When the mushrooms are spent, the compost left over can be spread out in your garden to populate the soil with great fungi!

Mushroom compost is simply the soil that edible mushrooms were grown in for commercial purposes. Eventually the mushroom production in that block of soil declines, and the soil is removed and bagged up for commercial sale.

The wonderful thing about mushroom compost is that it has a high amount of fungi – mycorrhizae – populating the soil, which benefits your garden soil by populating your garden with healthy fungi that will help feed your plants and retain nutrients so that plants can access them.  Mushroom compost is a win-win for everyone!

Other Compost Types

Manure is composted in piles that are turned frequently

The piles of manure after mucking horse stalls and cow pens can be made into wonderful fertilizer just by composting it. The reason we don’t put raw manure in gardens is because of the ammonia content (too much nitrogen burns plants and kills beneficial microbes) and the sulphur and methane compounds (which is what you smell). Composting breaks down these compounds into inert, bioavailable forms which benefit your plants.

There are other types of composts you can buy.  Composted manure, for example, is a very popular addition to garden soils.  Popular brands include Black Kow, Black Velvet, and Espoma Chicken Manure.  There are also those who sell mixtures of composted plant materials and manure (we actually carry one of those right now).

If you own farm animals, you should compost your animal’s droppings before adding to the garden. This will help avoid nitrogen overload in the soil which can burn your plants, and it also helps decrease the odor of fresh manure. 

Garden Trivia: One of the few animal droppings you don’t have to compost first before adding to the garden is Rabbit droppings.  You can add those directly to soil. 

Additives in Compost

Depending on what kind of compost is being made, there are some additives that are helpful, depending on the goal of the mix and the gardeners typically using it.  Here’s some of them, and their properties, so that you can make more educated decisions!

Perlite being added to a soil mixture in a container planting

Perlite is a unique material that looks like Styrofoam balls.  It’s NOT Styrofoam balls, however. 

(Here’s where I get to put on my Bill Nye Bowtie! I’m a nerd, after all):

Perlite is made from volcanic glass that is formed when newly-formed hot obsidian touches water.  It makes a glass with a high water content (remember your chemistry class?  Glass is a LIQUID!)

When heat is applied to the perlite, because of the water trapped inside, it puffs up into these little white balls – sort of like popcorn in an air popper!

close up of perlite

This is a closeup of Perlite. These soft, kinda squishy balls, are key to great mix of aeration and water retention in your soil.

Now these puffy balls of perlite, on the surface of each little ball, has a whole bunch of nooks and crannies.  Air nestles itself in some of those little nooks and crannies.  In others, some water will get cozy.  This means that perlite aids in soil aeration AND water retention AT THE SAME TIME!  It’s pretty awesome stuff.

Now, you’d use perlite in mixes of soil for things that you want to dry out – to create more well-draining soil.  So, for things like cacti and succulents, a perlite mix is a good thing. 

Perlite is also great for making Forsythe pots which are used for rooting cuttings.  It allows the perfect mixture of air and water to grow roots.


Sprouted grains growing in vermiculite

Vermiculite looks like little worms, doesn’t it?! With the crags and folds, vermiculite has an immense amount of surface area in a very small space. The tiny spaces between the “pieces” are the perfect place for water to be stored due to the capillary action of water (one of water’s chemical properties, based on its molecular surface tension – yes I realize how nerdy I am, but it’s so fascinating!)

Vermiculite and Perlite are often thought to be interchangeable.  They’re actually not, and here’s why:

Vermiculite is made of (I’m still wearing my Bill Nye bowtie here) a group of minerals that resemble Mica (the stuff that makes your car paint sparkly); they are silicate minerals.  Silicate minerals can by hydrated – in other words, they can absorb water.  You know when you get a new purse, or a package of beef jerky, and there’s a little “silica gel” packet in there?  Silica is a mineral that absorbs water!!!

Anyway, vermiculite is made from compressed dry flakes of silicate material which is absorptive and spongy.  It interacts with potassium, calcium and magnesium in your soil, and actually helps to raise the pH (make it more alkaline) even though vermiculite itself is pH neutral (7.0).

vermiculite, close up

You want to use vermiculite in mixes that need to stay damp and not dry out.  For instance, root crops like beets need consistent moisture – not flooding! – to grow consistently to the proper size.  Vermiculite helps keep the soil consistently moist and avoid drying out by its ability to hold and release water when needed by the plants.  It’s also great for plants that need more “swampy” conditions, like your swamp mallows and the houseplants like the “money tree” (Pachira aquatica).

Vermiculite doesn’t aerate as well as perlite, so if there is a heavy concentration of vermiculite in the soil for plants that don’t need damp soil, they may suffer from root rot pretty easily.

So just remember:

Perlite is for drainage and vermiculite is for water retention.


pelletized fertilizer

Many commercial composts add fertilizer.  The label will tell you if it does or doesn’t, because anything with added fertilizer will have to have an NPK rating on it.

In compost, added fertilizers tend to drain away quickly. Sometimes they use time-release fertilizers which give a consistent feed for a certain number of weeks or months.

They usually tell you on the packaging if it’s slow release fertilizer or not (because it’s a selling point for many gardeners!).

Homemade Compost

Making compost at home takes a little work, but it's worth it!

You can compost almost anything from the kitchen except meat and dairy (and even that in small amounts is possible with special care).  Clippings, peelings, non-greasy non-glossy shredded paper (like newspaper, mail, cardboard, paperboard, etc), grass clippings, leaves, pulled weeds (recommend weeds without seed heads!), and more can all be composted to create wonderful nutrient rich additions to your garden.

The beautiful thing about homemade composts is that you’re keeping organic matter out of landfills.  At the landfill, organic matter is converted to methane and contributes to greenhouse gas emissions and global warming.  By composting at home, you decrease your carbon footprint AND you know exactly where your compost comes from.

beautiful vegetable garden with a boy picking peppers

Want to learn more about how to compost, and about people who use composting to help them produce their own food? Check out my past articles on the subject:

Composting is the New Trendy Socially-Responsible Practice

Leaves Aren’t For Landfills

Simple Sustainability to Declare Your Independence

Hope you enjoyed today’s blog about compost, and that it was informative to you. Tell me, do you compost?  If not, what’s your favorite commercial compost that you’ve had success with in your yard or garden?

Until next time, Keep Growing!



P.S. Here’s links to some of our commercial compost we have for sale here at Shell’s!  If the link is dead, we are currently out of stock, so check back soon!

Timberline Lawn & Garden Compost & Cow Manure Mix, 1 CF

Mushroom Compost, 40 LB bag

Black Kow

Espoma Organic Chicken Manure

Happy Frog Potting Soil (contains composted forest material)

Ocean Forest Potting Soil (contains composted forest material and sea kelp)



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