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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. 

What is compost used for?

“What is compost used for?  What’s the difference between compost and manure, or compost and topsoil, or compost and mulch, or compost and…?”

These questions (or some variation thereof) have been posed in Google searches by thousands of McGill Compost website visitors over the years, suggesting a broad lack of understanding on the part of the general public about soil products, in general, and compost products, in particular.

They tell us there’s much more work to be done before compost becomes a solid, steady blip on the soil amendment radar. 

It doesn’t matter whether the compost purveyor is municipal, commercial, or non-profit, or if it’s selling B2C or B2B (or both).   Compost manufacturers, distributors, and retailers can all benefit from marketing programs and advertising campaigns that include a healthy dollop of consumer education along with branding, product descriptions, and price points.

In a recent BioCycle article, Dr. Sally Brown reminds us that “… feel good sayings without quantitative information to back them up doesn’t always help to move the product. To a city engineer, these feel good statements can make you sound like a new age guru pushing a dietary supplement rather than a knowledgeable resource with alternative solutions.

Ouch.  

To be fair to all the OGs out there, in the early days of the composting industry, the only thing we had to peddle was feel good. There was little bona fide research or hard facts that demonstrated compost’s effectiveness to a customer,  just anecdotal evidence and side-by-side field photographs comparing compost and no compost applications.

McGill’s own economic impact studies, conducted in the early 2000s and funded by the state of North Carolina, were among the first to investigate dollar benefits related to compost use.  The research may have been simple by today’s standards, but it validated information our agricultural customers had been telling us for nearly a decade – and provided a solid foundation for the growth of our compost sales program into high-value markets.  (READ: the 2000 and 2001 McGill study reports)

But dollars and cents are only one part of compost’s amazing story that started with fertilizer value, but now just keeps going and going and going to include everything from food waste recycling to stormwater management to carbon storage.

Yet, the abundance of compost’s benefits seems to be a message that hasn’t been told loud enough or long enough or often enough to reach the ears of the majority.  There are still too many stormwater plans out there that don’t fix the soil as a critical first step,  communities that burn or bury compostables, and farmers who don’t use compost on conventionally-managed fields.

Talking who, what, when, where, and how when promoting compost is good.  But today, when a potential customer, policymaker, or specification writer is searching the web, s/he also wants to know the why — backed up with facts and figures.  Why is compost the right solution for their particular problem?   Why is it a better choice than amendment X, Y, or Z?

What is compost used for?

Adding macro and micro nutrients, building soil organic matter, replenishing and sustaining soil microbes, improving nutrient uptake and plant disease resistance, creating pore space, adjusting pH, absorbing rain impact energy, degrading pollutants, storing carbon —  it’s a lengthy benefits list for a single product that just happens to be “green.” 

Fortunately, unlike decades past, cyberspace is now loaded with scientific studies that provide meaningful data related to compost performance.  This is news the marketplace needs to hear.    

For example, it’s true to say compost alleviates compaction.  But when presenting to engineers, would it not be better to also include a link to or slide of this table that compares compost’s performance to other solutions, showing it among the best?

Or when a city is making decisions about its stormwater management strategy, why not share some comparative costs per gallon retained for various retention solutions discussed in Milwaukee’s Green Infrastructure Plan (see Page 63)?

“Compost will hold 10 times its weight in water” is good for visualization.  But how does it help a stormwater system designer calculate potential water and cost savings for mandating compost use vs. rain gardens or storage tunnels?  

These are the types of statistics a decision-maker needs to see when considering options:

  • A typical compost is about 50% organic matter. 
  • Every 1 percent increase in soil organic matter adds 16,000 gallons of water-holding capacity per acre foot.  
  • At only 2 percent organic matter, soil can hold all the rainfall from a typical rain event — around 1 inch or 27,154 gallons. 
  • A 1 percent increase in topsoil organic matter also stores about 60 tons of carbon per acre.

While specific numbers may vary depending on the study and/or source, the core message — that compost can be the better choice — remains constant. 

Researchers say the majority of today’s buyers do their due diligence and make purchasing decisions before reaching out to vendors for that all-important “first touch.”   If true, it’s more important than ever that brochures, point of sale displays, websites, or other outreach tools make the effort to quantify as well as entice. 

The environmental benefits of compost use are still an important part of the message. But the days of the easy sell to a predisposed customer base are long gone.  Now it’s time to win over everyone else.

Expansion of both B2C and B2B markets depends on the industry’s ability to effectively silence skeptics, motivate fence-sitters, and educate the uninformed — while keeping products (and services) cost-competitive.

Facts and figures will play a big role in that education effort.

Granted, there are lots of challenges ahead, and we do need more research of relevance to compost users to help fill quantitative gaps.

But composting is at an unprecedented place in its own history.  For the first time, the general public is eager to know more about what composting and compost use can do to positively impact a wide variety of issues. 

“What is compost used for?”

For the continued growth and wellness of the industry, research-based numbers need to be part of that all-important answer. 

Can I compost cooking oil and grease?

Is it possible to compost cooking oil and grease?

A lot of cooking fat, oil, and grease (FOG) goes down the kitchen drain.  Commercial kitchens install grease traps to collect the mess before it enters public sewer systems, diverting this waste to alternate disposal.

But the typical home kitchen does not, and the practice can clog pipes and negatively impact wastewater treatment systems.

Yes, it is possible to compost FOG.  But for the home composter, volume reduction and reuse is recommended as the first and best management strategy.  Adopt some of these kitchen practices to reduce and reuse to minimize volumes requiring composting or disposal:

REDUCE   

  • Opt for the oven or air fryer instead of deep or pan frying.
  • Spray oil onto food or into pans to lightly coat before cooking instead of pouring oil into the vessel for significant volume (and calorie) reductions.
  • Wipe cooking vessels with a paper towel before washing to remove excess oil.

REUSE

  • Many fats and oils (bacon, peanut, etc.) can be reused.  Cool and pour through a coffee filter or strainer into an airtight container and store in the fridge for up to a month.  
  • Allow cooking juices to cool.  Skim/remove the fat that congeals on the surface and freeze to use later to flavor veggies, soups, etc.   

RECYCLE

  • Check with your public utility to see if there is a FOG drop location in the community.
  • Add cooking grease to the food waste bin if your community composting operation can accept it.

COMPOST AT HOME

  • Small  volumes (up to 1 cup) of plant-based oils are best for home composting.  Simply pour over pile and blend in.  
  • Also compost the paper towels used to wipe oil from pans and kitchen surfaces.      

DISPOSAL

  • Pour waste oil into a non-recyclable can or bottle.  Seal prior to disposal. 

Is it really a good idea to make compostable waste go away and never come back? 

Each year, taxpayers collectively spend millions of dollars to burn or bury compostables.  Much like a tribe of ubiquitous Gollums, they just want garbage — the biodegradable and putrefying fraction of the municipal solid waste stream – to go away and never come back. 

The desire to make disagreeable discards disappear into fiery furnaces or burial mounds is understandable.  But is it wise?  Is it fiscally responsible?  Is it really a good idea to make organic waste go away and never come back? 

Nature recycles everything 

Rocks weather and erode, creating sediment. With heat, pressure, and time, that sediment becomes rock again.  Plants and animals feed and drink from the earth, die, and decompose to replenish the soil that will sustain future generations of flora and fauna.  Water drops from the sky as rain, filters down to aquifers, upwells and evaporates back to the clouds to fall once more. 

In a fantasy land, it may be possible to keep using resources without a thought to replenishment.  But in the real world, organic waste – the decaying residuals of once-living things – must be recycled back to the soil to maintain life-critical soil functions.   

Some seem to think the destruction of organics to make energy is more important than rebuilding soil.  But pushing an organic-waste-to-energy agenda by sacrificing the soil makes no sense. Humans managed to survive for millennia without electricity and centralized energy systems.  Without soil’s life-essential contribution to food and clean water, people face extinction in weeks.  

So, which is more important, energy or soil? 

Make energy and rebuild soil?   

Organic waste from developed societies includes all types of vegetation, food, manures … even compostable plastics.  When turned into a quality compost, these once-lost resources can be used by anyone anywhere to replenish depleted soil.   

Happily, making energy and building healthy soil does not have to be an either/or proposition.  It is possible to extract energy from organic waste without destroying the beneficial properties that make it valuable to soil.   The organic waste streams from these processes can then be used as feedstocks in the manufacture of compost products. 

Unhappily, energy production from biomass is one of the most expensive ways to make energy.  Even solar and wind power can be more cost-effective. 

Furthermore, bioenergy technologies based on anaerobic digestion of organics are still too pricey to be practical in many places.  Where they do exist, the waste stream (digestate) is not always put to highest and best use (i.e. composted).  Instead, residuals may be landfilled or relegated to low-dollar-value reuse. 

But one day, as more communities opt to restore natural soil replenishment cycles and energy generation technologies become more efficient, extracting energy from biomass, followed by composting and compost use, can become the system of choice for organic waste management. 

In the meantime … 

The importance of healthy soil 

Where humans live, topsoil has been scraped away or eroded.  Nutrients are used up.  Compaction has destroyed the pore spaces essential to the transport of air, water, and microbes.  Without a regular infusion of new organic matter to correct these deficiencies, soil dies.   

There are lots of processes for generating energy, but there’s only one way to replenish disturbed soils in developed areas – feed them a good, wholesome diet derived from organic waste converted into compost.   

From farms to lawns to sports fields, soils require periodic applications of compost.  There’s no other way to easily and economically provide soil with everything it requires to retain water, nurture vegetation, and create the type of environment soil microbes need to support nutrient uptake, contribute to disease resistance, and degrade pollutants. 

The best news? In many metropolitan areas, efficient, high-rate composting – the type needed to successfully manage big, urban waste streams – costs no more than landfilling or incineration.  Often, recycling at a modern, industrial composting operation can be more affordable than traditional disposal.   

Composting makes organic wastes go away, but they come back as enriching soil amendments.  Biodegradables need to keep recycling, just like they have since the beginning of time. 

Breaking the natural soil cycle by incinerating or burying compostable waste is a bad idea that should go away and never come back.

VIEW THE SLIDESHARE:  Addicted to convenience

How to make compost fast

The desire to make compost fast can be driven by space restrictions, the need for more product, or simple impatience.   It’s a common goal for composters everywhere, from the backyard to industrial facilities.

Unfortunately, wishing will never make it so.  The speediest course from raw feedstock to finished quality compost is a series of steps controlled by the person doing the composting.  Skip or bungle just one, and biodegradation could slow or even grind to a halt.

It doesn’t matter whether you make compost by the tumbler or by the ton.  If you want to make compost fast, follow these steps:

  1. Consider carbon-to-nitrogen (C:N) ratios when mixing every batch.  Base mixes on the C and N percentage of each feedstock, not feedstock volume – it’s not buckets of “brown” to buckets of “green.”   Learn more about calculating C:N ratios.
  2. Get the blend right with uniform particle size, good porosity, no clumps or marbling of feedstocks.  
  3. Maintain a desirable moisture level throughout primary processing.  Don’t expose the composting mass to weather or allow it to dry out.  Add moisture, as needed.   Learn more about composting moisture levels.
  4. Keep air moving through the pile.  This allows microbes to breathe and removes excess heat.  Invest in a temperature probe and adjust air flow to maintain ideal temperatures.       

Master these basics to make compost fast.

Compost is soil’s superhero

Sure, compost adds nutrients. But that might be this soil amendment’s least important function. 

Quite often, articles will mention compost as a replacement for some or all of the nutrients that might be provided to plants through applications of synthetic (man-made) fertilizers.   

That’s certainly true.  Compost delivers the macronutrients nitrogen, phosphorus, and potassium (NPK), plus a slew of plant-essential micronutrients that are missing from most synthesized fertilizer products.  Compost provides plants with a wholesome, well-rounded meal, not the nutritional equivalent of junk food. 

But what these fertilizer-focused articles rarely mention is the fact that the real value in compost use is not related to feeding plants, but to feeding soil … and soil does require a wholesome diet to function as a true soil and not a dead substrate. 

Compost feeds soil

Providing plant nutrients is just one of many soil functions.  Worms and other creatures that live in healthy soils help to physically break down food sources, then microbes take over to convert that food into plant-available form. 

Both physical and microbial conversion depend on a soil environment that can support those lifeforms.  If the soil is chronically too wet, too dry, too compacted  yada, yada  then it can’t support a healthy soil ecosystem.  That plot of ground may not be soil at all, but lifeless dirt. 

To countermand the impacts of human activity, disturbed soils require regular program of replenishment that includes organic matter and microbes.  Compost provides both.  Compost feeds soil.

Then, when it rains, soil retains that water, reducing runoff.  When runoff is reduced, so is erosion, sedimentation, and water pollution.  Because soil microbial activity also degrades pollutants, any stormwater that does run off is cleaner.  

That same microbial activity can help neutralize some soil-borne diseases, too. 

Improving plant nutrition, aiding in disease control, reducing water pollution, and retaining water are all important soil functions. 

But wait, there’s more. 

Compost as a carbon sink 

The build-up of greenhouse gases in the earth’s atmosphere is cause for concern.  As more greenhouse gases flood the atmosphere, temperatures increase. 

This rise in global temperatures influences many things, erratic and extreme weather being one of the most visible.  Subsequent climate shifts can impact people, crops, and livestock for hundreds of years. 

When used to amend soils, compost sequesters carbon.  This means the soil will act as a carbon “sink,” capturing and holding carbon in stasis – but only as long as the soil remains undisturbed.  When the soil is tilled, that carbon is released. 

Extensive use of compost for perennial crops and other long-term application(grasslands, tree farms, utility easements, etc.) can positively impact atmospheric conditions by reducing greenhouse gases.   

At the same time, the addition of compost rebuilds a topsoil layer that has been eroded or scraped away by farming, development, and other human activity.  Since topsoil loss has been identified as a significant threat to planetary health, second only to population growthits restoration is a global priority.   

At a time when nearly a third of the world’s arable land has become unproductive in just a few decades, compost really can be that superhero swooping in to save topsoil, save water, save the atmosphere, and save the planet. 

Comparing costs per gallon retained 

Soil amendment is one of the least expensive ways to collect and manage stormwater 

Manage water where it falls.” 

This sound advice is the foundation of the Milwaukee Metropolitan Sewerage District’s Regional Green Infrastructure Plana program that identified soil amendment as one of the least expensive ways to manage stormwater.  At 28 cents per gallon, improving soil is second only to native plantings in lowest cost per gallon retained. 

Green roofs?  $4.72 per gallon.  Those fancy-schmancy deep storage tunnels?  $2.42 per gallon.  At $1.59 per gallon, even pretty little rain gardens cost more than five times that of simple soil amendment. 

Milwaukee is not alone in promoting soil amendment as a first line of defense for stormwater management  For example: 

  • Denver and GreenleyColorado, require compost use for new landscaping, as does Leander, Texas. 
  • Some state Departments of Transportation (DOTs) now routinely specify compost.  A few years ago, the Texas DOT said it was the largest single market for compost in the U.S. 

In an urban environment, opportunities for soil amendment abound.  City parks, athletic fields, planters, urban lawns, highway medians and easements, foundation backfill – anywhere there’s soil, there’s opportunity for inexpensive water retention. 

Every 1 percent increase in soil organic matter (SOM) content adds an additional 16,000 gallons of water-holding capacity per acre foot.  A site managed to maintain soil organic matter at only 2 percent can hold all the water of a typical rain event (1 inch or less), which is 27,154 gallons per acre.     

In fact, at 5 percent SOM, the soil can retain the water equivalent of nearly 3-inches of rainfall.  In some regions, this equal95 percent of all storm events. 

Soil amendment may not solve all rainfall issues, especially in downtown areas.  But managing water where it falls can be the most sensible, efficient, environmentally- and economically-prudent strategy for “first line of defense” stormwater management.