What’s the difference between compost and peat moss?

Compost is manufactured from recycled materials derived from plants and animals.  Peat moss forms naturally over many, many years – also from decaying plants and animals.  Both are rich in organic matter.  But it takes so many years for nature to form peat moss that the product is not considered “sustainable.”  Peat also tends to be too expensive to be used in large projects.  Fortunately, compost can be substituted 1:1 for peat in any media mix or soil recipe.  

FAQ: Do I have to rake fall leaves?

Nature drops fall leaves for a reason, and it’s not to give sightseers an excuse to tour the countryside.  Those red, yellow, and gold gems will eventually decay to help fertilize the soil for the coming season.   So, no, leaf raking is not a necessity. 

Know, however, that the fall leaf drop can wreak havoc on stormwater systems.  One should, at the very least, make the effort to keep those leaves well away from stormwater inlets and  flow pathways.

Use a mulching mower to break up the leaf mat and accelerate biodegradation once that colorful blanket starts to fade.

If you can’t get through October or November without grabbing a rake, rough chop some of those leaves and use them to mulch planting beds and gardens.

The remainder can go to composting, of course.  Add them to your backyard compost pile, or prep them for curbside collection following your municipality’s guidelines.  And, please, do remove plastics, metal, glass, and other contaminants before moving those leaves to the curb. 

FAQ: Is fall a good time to use compost?

Most definitely, yes.  In fact, some believe the fall season is the best time to add compost to lawns and gardens.  For grassy areas, sprinkle a little over the surface and rake in.  For planting beds, add compost and work into the top layer of soil.  Alternatively, just leave the compost to sit on the surface of the planting bed and allow Mother Nature to work her magic over the winter months.  Cover the surface with leaves or other mulch to help retain moisture.  When spring planting season rolls around, the soil will be ready for you.  Compost products will vary, so always follow the manufacturer’s recommendations about exact amounts to use for specific applications.  You can find McGill’s recommendations here.

FAQ: How does compost protect drinking water?

Primary sources of drinking water include wells, lakes, reservoirs, and rivers.  Compost will protect drinking water sources by breaking down pollutants and reducing erosion/siltation in runoff.  Microbial activity and absorption of rainfall energy are among the mechanisms at work.

Soil microbes break down many chemicals — like petroleum products – during feeding activity, severing molecular bonds and reducing complex compounds into simpler, more benign forms.  In fact, compost is used to remediate petroleum contaminated soils at airbases, underground storage tank removal sites, highway accidents, and similar clean-up projects.

Compost’s organic matter content cushions rain or irrigation water.  When water hits the ground, that energy is disbursed, and fewer particles are dislodged.  That same organic matter also absorbs more water, resulting in less runoff.

In addition, the use of compost reduces the need for chemical input on farms, turfgrass, and in the landscape, which also helps to protect drinking water sources.

FAQ: How do I sterilize soil?

When making your own potting soil from native soil or trucked in topsoil, it’s a good idea to sterilize that dirt to kill things like weed seeds and diseases before mixing with compost and other ingredients.  Large swaths of ground can be treated in-situ (in place) using plastic and the sun, but it takes time.  Fortunately,  small batches can also be treated using kitchen appliances.  Here’s a how-to article.  

How to make topsoil

When you order topsoil, do you really know what you’re getting?  

In some developed areas,  most of the topsoil has been scraped away or eroded.  What passes as topsoil is really subsoil – nearly dead dirt.  It will not function like good soil.

The good news?  You can make your own, be assured of its quality, and likely pay less than having topsoil trucked in.  Here’s how:

FOR EXCAVATED SOIL:  Mix the native soil with compost at a ratio of about 1 bucket or shovelful of compost to every 2 of soil.  A 30 percent compost content is recommended for raised beds and containers.  

FOR IN-SITU SOIL:  Work 2-3 inches of compost into the top 6-8 inches of native soil.

Compost is a very “forgiving” material.  It’s hard to use too much  (though you shouldn’t use it instead of topsoil),  and as little as 1/8 inch can be enough to give your soil a boost.

Whatever the amount, be sure to blend well so the compost is evenly distributed.

How can you tell if a soil is good or bad?  

The ideal soil for growing things will be a mix of sand, clay, and organic matter.   If having your soil tested, be sure the report will include these parameters.

Forging ahead without the soil test? The first part of this article describes various soil types and provides simple methods of identification.  

If you need to add sand or clay in addition to compost, ask your landscape supply yard for a custom blend.

According to this article,  most soil scientists agree that 50% pore space, 45% mineral matter (sand, silt, clay), and 5% organic matter make up an ideal ratio.  A typical compost is 50%-60% organic matter (dry weight). 

How much compost for my garden?

Compost makes a great addition to any garden plan.  But how much compost do you need?

A new plot in sand may require wheelbarrows of the stuff.  But if you are digging up a patch of lawn that has seen repeated compost applications over the years, the soil beneath the sod should be in pretty good shape.  A sprinkle might be all that’s needed.

How can you tell if the soil is good?  

The best method is soil testing.  (Contact your county Cooperative Extension Service for more information).  But you can use visual clues, too.  

Weeds like purslane, crabgrass, and dandelion are signs of a troubled soil.  

Stick a spade in the ground and turn over a shovelful of soil.  If it’s sticky and looks like modeling clay or dry and resembles beach sand, you’ve got big problems.  Fortunately, your soil is probably somewhere between these two extremes. 

Is it dark brown and loose?  Are there earthworms?  That’s what you want to see.  

How much compost do you need for a garden?

If building raised beds or container gardening, the soil blend should be about 30 percent compost.  When breaking new ground, incorporate 2 to 3 inches into the top 6 to 8 inches of soil.  

If your soil is very hard,  and you are planning deep rooted vegetables like tomatoes,  consider digging a little deeper.  Maintain the compost-to-soil ratio at about one part compost to two parts soil.

For an established garden with decent soil, just rake an inch or two into the surface before planting.   A 1/8 to 1/4 inch layer of compost sprinkled on the surface as needed throughout the growing season can revitalize flagging rows or containers.  The compost will feed your plants when you water. 

Three to 4 inches of compost can also be used as mulch during the growing season or as blankets when putting beds to sleep for the winter.  However, don’t pile compost up against tree trunks and stems of woody ornamentals.   

Our compost calculator can help you determine how much to buy.       

How much does compost weigh?

Depending on moisture level, figure 2 to 2.5 cubic yards of compost per ton.  A one cubic foot bag of compost will weigh about 40 pounds (1 cubic yard = 27 cubic feet).

A product shipped at 30 percent moisture will weigh less than one at 60 percent when it crosses the weigh scale, resulting in more cubic yards per ton than the wetter material when delivered.  

This may be good for keeping transportation costs low. But it also means the microbes responsible for aerobic degradation of the composting mass might die of thirst.  Weights that are too high could be indicative of low oxygen levels resulting from compaction and/or too much moisture — again, not good for the beneficial microbial populations.

An ideal compost will be 40-50 percent moisture.

Are compost and fertilizer the same?

Compost and fertilizer are not the same. But compost does have fertilizer value.

Wikipedia describes fertilizer as any material of natural or synthetic origin that is applied to soil or to plant tissues to supply one or more plant nutrients essential to the growth of plants.”

Compost’s nitrogen, phosphorus, and/or potassium (a.k.a. NPK) values are low compared to a synthetic fertilizer.  Some may add ingredients like urea to hike these macronutrient numbers.

That said, compost’s NPK value does have dollar value. The nutrients delivered by a compost product should be a factor in any input decisions involving synthetic fertilizer purchases.  Compost also adds a slew of micronutrients not typically found in common synthetics and improves nutrient uptake.

Compost feeds the soil. In turn, the soil takes care of the plants, offering a smorgasbord of nutrients, pest and disease resistance, and more.   But those nutrients are slow-release, feeding plants over time.  The benefits of a single compost application can stretch over multiple seasons.

Fertilizer’s sole purpose is feeding plants.  The primary function of most synthetic fertilizers is adding N, P, and/or K.  Application gives an immediate burst of nutrition.

Do you need fertilizer if you use compost?

For the home gardener, probably not, especially if that gardener is a long time compost user.

But for a commercial grower?  Maybe.  If the crop likes a punch of nitrogen (for example) at a certain point in the growth cycle, the addition of a synthetic fertilizer may be warranted.

However, the smart grower will carefully weigh the cost of any input against the expected return on investment. Sometimes, a lower yield will still net higher profits if input costs for synthetic fertilizers and pest control products are reduced or eliminated as a crop management expense.

Also, keep in mind that compost-amended soil reduces rainwater and irrigation runoff, which means more nutrients are retained in the soil.   This will impact synthetic fertilizer input requirement, as well.

The Compost Connoisseur 

Compost maturity and stability are not the same 

A mature compost is usually stable, but a stable compost may not be mature.  Yet, both products have their uses.  Though the term“maturity” and “stability” are often used interchangeably to describe compost, they should not be.  

Confused? 

Look at a red and green tomato.  Both are stable and edible.  But the green tomato won’t be mature until it turns red.  This work-in-progress tomato is a bit on the tart side with firmer flesh that holds up when fried.  The mature red one is sweeter, softer, and makes a great sauce. 

As distinct products, mature and immature composts have their specific characteristics and uses, too.  But like red and green tomatoes, they’re definitely not the same. 

Compost maturity and stability 

MATURITY  All organicwill eventually decay until nothing remains but atoms.  The trick is to reach a degradation phase where the easy stuff is gone, leaving only dark, slow-to-degrade, earthy-smelling material behind.  That’s a mature compost. 

Between the raw waste and finished compost, however, are a series of degradation steps that aren’t that beneficial to plants.  In an immature state, compost can release compounds harmful to plants, fight with plants for oxygen, and pull nitrogen out of the soil.  

Compost maturity is best determined by testing, which is a good reason to insist on seeing a recent lab report for the compost under consideration.  Maturity indicators on lab reports include: 

  • C:N ratios  
  • Germination rates  
  • Oxygen uptake  

Maturity assumptions based on curing time are also recognized within the industry, but may not be as reliable as testing. 

STABILITY  If a compost passes the maturity test, it is a stable, market-ready product.  In a mature compost, microbiological activity slows because all the “easy” food has been consumed.  

But there are conditions within the composting mass that can cause product to enter a stable state without reaching maturity. 

Compost that has been dried to remove moisture, for example, makes it lighter for shipping, but can exhibit reduced biological activity, as well.  The same thing happens if the pile is deprived of oxygen. 

Unfortunately, once moisture or air has been reintroduced, microbial colonies can reestablish and return to active feeding.  Pathogens can rebloom and odors resurface as the composting process resumes. 

Germination tests remain one of the best indicators of mature stability.  If the compost exhibits no indications of phytotoxicity in conjunction with good pH ranges and slowed microbial activity, then the product has probably passed into the mature range. 

If trying to evaluate stability while standing next to a pile in a landscape supply yard, look for: 

  • A light, porous, evenly-textured product that encourages good air flow 
  • A compost with sufficient moisture to stick together when squeezed in the palm of the hand without crumbling or dripping water 
  • A pleasant, earthy scent 

Selecting the right product 

In the absence of testing information, the easiest way to gauge a product’s maturity is to smell it.  Compost that smells like soil has likely reached a stable, mature state and is ready for use anywhere and by anyone. 

Product that still retains some pungency isn’t stable or mature.  It’s not quite ready for unrestricted use.  But, provided it has met minimum quality standards for pathogen and vector reductions (as specified by regulations), the compost can be applied in rural areas away from sensitive noses where its higher NPK value is much appreciated by farmers. 

Time and nature will finish the job of product maturation and stabilization.