Book Review Compost Science for Gardeners, by Robert Pavlis


Compost Science for Gardeners by Robert Pavlis

Compost Science for Gardeners, Simple Methods for Nutrient Rich Soil, Robert Pavlis,

New Society Publishers, January 2023. 224 pages, 6 x 0.52 x 9 inches, charts, diagrams and photos. $19.95.

Robert Pavlis has been a gardener for over 45 years, and is a very good science writer. I have previously reviewed Soil Science for Gardeners and Plant Science for Gardeners. This is a valuable, concise, accessible book for home gardeners, and also homesteaders, market gardeners, small-scale and large-scale crop farmers.

The book gives an introduction to the what and why of compost, and then covers the role of compost in the soil, the science of composting, compostable materials, managing the composting process, the options of piles, bins and tumblers, easy composting methods, vermicomposting, Bokashi composting, eco-enzyme composting, buying compost, compost tea, choosing a composting method, using compost and discarding compost myths. There are some almost cult-like groups with beliefs about how to make compost that are not science-based. The author has formed a Facebook group, Garden Fundamentals, you can join, to learn science-based information and help bust some myths yourself.

Garden Fundamentals logo

The introduction explains the importance of high organic matter in the soil, and the cycling of carbon and energy that can increase soil OM. Soil with more organic matter holds onto nutrients better, leaching less, keeping more nutrients in place for the crops. As gardeners we can help the process. We can leave extra plant material where it falls, spread tree leaves around our plants, and establish bug hotels. We can make compost from inedible and unaesthetic plant matter and use the mature compost to fertilize and build the soil, and feed the soil biology.

Nationally, 30% of garbage is yard waste and food scraps. At the landfill, these produce methane, a greenhouse gas with 25 times more global heating power than carbon dioxide. And then add on the pollution from the garbage trucks. It’s plain to see that making compost benefits everyone (except companies selling fertilizer).

There are quick and easy ways of returning garden waste to the soil (chop and drop), and there are labor-intensive ways that kill some weed seeds and diseased plants, and break down woody fibrous materials. You choose. When you do it right, there are no noxious smells. There are even methods you can use inside your house.

Screening a large pile of compost for the greenhouse beds. Photo Wren Vile

The Role of Compost

  • Mulch: keeps soil cooler, damper; may or may not reduce weeds.
  • Fertilizer: contains lots of plant nutrients including micronutrients, that are slowly and steadily released. Because compost has a high Cation Exchange Capacity (CEC, meaning it can hold lots of nutrients), nutrients stick to it, reducing the leaching rate.
  • Soil Builder: adds organic matter, improving aggregation in both sandy and clay soils, helping soil ingredients combine into larger soil particles, upgrading soil structure.
  • Water retainer: a 5% increase in organic material quadruples the soil’s ability to hold water.
  • Toxin remover: compost attracts and binds toxins, preventing plants absorbing them.
  • Acidity buffer: compost brings soil pH closer to neutral, from either side of the scale.
  • Microbe feeder and habitat: More microbes = healthier soil. Add compost, don’t add microbes! Provide the right conditions and they will multiply.
  • Reducer of landfills and greenhouse gas.

If you haven’t already read the author’s earlier book Soil Science for Gardeners, I recommend that. There is a brief description in this book, and charts and a diagram of the soil nitrogen cycle. Plants cannot use large pieces of organic matter, but need it to have it decomposed enough to release the ions. Ions from organic sources or bags of chemical fertilizer are identical. What is different is the ratios and mixtures of ions you are applying.

Tilling is controversial, because it destroys soil aggregates, and brings up weed seeds from lower in the soil profile. Tilling adds air to the upper level of soil, increasing the rate of decomposition of the organic matter. However, it has been found that the organic matter deeper in the soil increases after tilling, so that the total in the top 12” (30 cm) remains unchanged. This may be due to plants making deeper roots (roots are OM!). If you don’t need to dig it in, it is better for the soil and the planet to add materials to the surface.

Digging compost into our cold frames in preparation for fall planting.
Photo Wren Vile

What happens during the composting process? Understanding this helps you make informed decisions in selecting materials and managing the process. Larger life forms play a role in composting by mechanically reducing material to smaller pieces, making the foods accessible to microbes. These macroorganisms do not thrive in hot conditions – they leave when things heat up, and return later. It doesn’t work to second-guess what the compost pile needs. Adding earthworms doesn’t help. They’ll make their own way when conditions are right.

Composting happens when microbes decompose organic matter. Different microbes will self-select for the conditions you provide, just as macroorganisms do. They will multiply and thrive if temperatures and moisture suit them.

Plants are made of cells, and cells are made of molecules. Manure is plant matter that an animal has started to decompose. It’s still made of molecules, mostly unchanged as yet. After composting, all the large molecules have been changed into smaller, simpler molecules: amino acids, simple sugars, the stuff that microbes seek out for dinner. After dinner, and also after life, microbes release nutrients that plants can use. Compost happens!

Here is a clear explanation of the various stages of hot composting and the various kinds of microbes active during the different phases of the process. Worth buying the book for this alone! If you have a lot of seeding weeds, choose a hot composting method, but also chose better gardening techniques that control weeds!

At a garden scale, it will take at least 3 warm months to complete a hot-composting process. In colder climates, it will take 4-6 months or more. Cold compost piles can take 1-2 years. Commercial compost can be “made” in two weeks, but it needs another month to mature. “The first phase of bokashi is done in two weeks, but it is not really composting,” says the author.

We are encouraged to understand the C:N ratio of the materials we use, rather than use the simplistic (and confusing) Browns/Greens concept. Mostly we are feeding microbes, and their perfect food has a 24:1 C:N ratio. There is a helpful table of the C and N content of various compost materials you can use to calculate a recipe, using what you have available. The author offers an Accurate Calculation Method, an Easier Method, and an Even Easier Method.

Don’t worry about the pH. You don’t need to add lime. Home-made compost is usually in the 7.0-7.5 range initially, and drops a bit once in the garden.

A large proportion of the nutrients in finished compost are only released slowly (over maybe 5 years). If you run short of compost one year, don’t worry, your soil probably has enough from previous applications. When is a pile of compost ready to use? Try the Seedling Test. Put some compost mixed 50:50 with soil in a pot. Compare with a pot of just soil. Sow some quick-germinating seeds in each pot. As they emerge, compare the seedlings in each pot. If the plants grow equally well in both pots, your compost is fit for purpose. If the seeds in the compost/soil mix don’t emerge, or are stunted, allow the compost to age longer.

Robert Pavlis has three lists of compostable materials: Good, Bad and Controversial. He addresses antibiotics in animal manures, herbicides in animal fodder and yard trimmings; unnecessary worries about coffee grounds and various food scraps; eggshells, woody branches and used potting soil (OK but pointless); paper and its possible included toxins (not enough to worry about, in the author’s opinion, but not a particularly useful compost ingredient anyway).

The controversial ingredients include diseased plant material (know which disease, advises Pavlis); “compostable” plastics (they don’t break down using garden compost methods); human waste (too much sodium in urine, maybe transmissible diseases in feces); pet waste (maybe your own dog or cat, whose parasites and diseases you already risk, but not other people’s pets, unless you do a good hot composting method); toxic plants (diluted by other ingredients, digested by microbes, don’t worry); weeds (if you don’t let weeds seeds, you won’t have to worry about the compost; if they do seed, you’ll need hot composting the render them unviable; pernicious perennial weeds are best killed before composting); wood ash –  no point as it doesn’t compost, useful to add directly to acid soil.

Bad composting materials include “disposable” diapers (contain plastic and hydrogels); thorny plants; dryer lint, carpet fluff, vacuum cleaner bag contents, fabrics (these days these are largely synthetic fibers or cotton treated to be crease-resistant).

Compost-making is both art and science, and individual gardeners have their preferred twists on the basic method. Basic principles include

  • Location: indoors or outdoors? Indoors limits your options of method. Outdoors, you’ll need a water supply, proximity to the garden and other sources of materials (truck access?), a flat area with drainage and sunshine, and distance from neighbors. Check local laws.
  • Storage of ingredients: to use a hot method, you’ll need to store ingredients until you have a quantity and balance of inputs to build a pile. If you can’t do this, go for a cold system.
  • Air: turn the pile, or stir with an aerator, or make the pile with vented piping included, or layer the materials as you make the pile.
  • Water: add some every few inches as you build the pile. When you turn the pile, squeeze some of the material – it should be damp like a sponge, not sodden, not dry. Add more as needed. In wet climates, add a roof or a tarp over the top. If the pile gets too wet, turn it and fluff it up.

Get a compost thermometer, and once the pile reaches 145ºF (63ºC) – possibly as often as once a week – turn it to mix things up and start it reheating. Compost tumblers make turning easy. Three-bin systems give you somewhere to turn the pile into. A fork is the best tool for turning compost. One way to speed things along is to pre-shred your ingredients, perhaps by spreading them on a patch of grass and mowing them.

You do not need to add compost activators. These may be just microbes, which you should have plenty of. Or they may contain some fertilizer, in an expensive form. You don’t need to add phosphorus or potassium, but you might benefit from adding some nitrogen. Urine diluted 10:1 with water can provide that.

Once the pile no longer reheats, you have reached the curing stage, which takes about two months. Immature compost has a high C:N ratio, and is acidic. It could damage plants. If you are spreading your compost on the soil rather than incorporating it, you don’t need to cure it. This minimizes leaching. If you plan to dig it in just before planting, better to fully cure it first.

There is a troubleshooting chart of things that can go wrong and how to fix them. There are some photos and tables of pros and cons of each outdoor composting system. Resist any urge to turn your compost tumbler more than once a week, or you will disrupt the heating cycle and slow things down.

Pit and trench composting are methods involving gradually filling holes in the garden with compost materials and then covering with soil. This method works well for kitchen winter and spring, when there are fewer other ingredients. A keyhole bed with a central cylindrical cage for compost materials is a version of this idea.

There are electric “composters” which grind and dry kitchen scraps. They do not actually compost the food scraps, or even finely grind them. They use your money to produce dried food scraps, not fertilizer. And they use electricity doing it. When mixed with soil, the food rehydrates and grows mold.

Six worm bins.
Photo NCSU

Vermi-composters are bins holding worms, food scraps and other organic material, which together produce worm castings, which can be used as fertilizer. Vermicomposting is faster than traditional hot composting and can be done indoors, even in winter. The book contains enough detail for you to know whether this practice is one you want to try.

Microbes are the worms’ main food. Worms only digest 5%-10% of their food intake. The rest is excreted, along with a lot of microbes. Learn how much to feed, so that it has mostly gone by the next feeding. 1000 worms (1lb, 0.5 kg) will eat about 0.5lb (0.25 kg) each day. When food runs out, the worms will eat the bedding. Shredded newsprint, fall leaves, aged wood chips and more, make good bedding. There is a trouble-shooting chart.

The worm bin material (“vermicompost”) is a mix of worm castings, bedding material, uneaten food scraps, nutrients, worms, worm egg cocoons and microbes. While the worm bin is active, leachate liquid drops out from a drain hole in the bottom of the bin. This contains organic matter, nutrients and microbes. It can get smelly. It can be diluted 10:1 with water, to use on potted plants, or to water the garden.

Vermicompost will be ready to harvest 6-24 weeks after setup. Ideally, about 50% of the bin will be bedding and compost, and 50% castings. You can use the castings and compost mix in your garden right away. Worm castings have 10-20 times as much microbial activity as soil or most other forms of organic matter. They compost themselves once in the garden. To use for potting soil store it for two months, then mix 20% by volume in your potting mix.

The composition of vermicompost is a little higher in N than regular compost made from the same materials, and the potassium is the same, but the phosphorus is almost four times the level in the regular compost, which can be a problem if your soil is already high in P.

Next the mysteries of Bokashi fermentation (often called composting) are revealed. It’s an anaerobic process, similar to making silage, but usually done in small batches for small gardens. Most pathogens are killed. Waste organic matter is combined with sweetened “Bokashi bran” which contains fermentation microbes in a lidded bucket. Bokashi can be made indoors, and is a useful option in climates with cold winters. All kinds of food can be included with no worries about rodents.

Ignore the claims about “Effective Microbes,” because a study has found them unnecessary. Farmers often start Bokashi with naturally occurring microorganisms rather than buying the 80-microbe EM-1 product. One study found. no difference between using indigenous microorganisms, yeast or nothing at all.

A dark liquid leachate is drained out of the bottom and used as fertilizer, diluted 1:50 with water. It is low in nitrogen, but high in phosphorus, sodium and chloride. See the photos in the book for proof that it is not a good solo fertilizer.

The full bucket is left for a couple of weeks, and then the material is either added to a compost pile or to a large worm bin. It is not ready to be used for plants. You could save time and just feed the raw materials directly to the worms. The pH of Bokashi is around 4 (quite acidic), whereas the pH of compost is about 7.

The Eco-enzymes process, also known as Garbage Enzymes, is similar to making Bokashi or sauerkraut, and is popular in some households in Thailand and nearby countries. It reduces the amount of garbage going to the landfill. The system relies on the microbes already on the surface of the foodstuffs. None are added. Anaerobic conditions prevent pathogens from growing.

Enzymes are proteins created in living organisms. They carry out most of the chemical reactions that take place in the cells, including digesting organic matter. To start an eco-enzyme process, combine 3 parts of chopped organic matter, 1 part of sugar and 10 parts of water in a closed container. Open the lid once a week to let excess pressure escape. Wait three months at room temperature. Then separate the liquid from the solid ferment.

The liquid contains acids, alcohols, bacteria, yeast and protease, amylase and lipase enzymes, as well as plant nutrients.  It can be used to fertilize plants, or as a cleaning product with antifungal and antibacterial properties. The solid ferment is similar to Bokashi ferment, and needs composting to be useful to plants.

A commercial compost windrow turner.
Photo by Pam Dawling

Not everyone can make their own compost in large enough quantities. Some municipalities collect compost materials and make compost, which is then sold locally. Because a hot composting process is used, there will be no pathogens or weed seeds. There are no national US standards for compost, so read the small print.

Bits of food packaging, microplastics (less than 5mm in length) and nanoparticles (smaller) will be in municipal compost. A 2021 US EPA study found 300 pieces of microplastics per gram (8,400 per ounce) of food waste collected from grocery stores. Make your own compost if you can!

Chemical contamination is another concern. Pesticide residues will mostly (not entirely) decompose during composting. Leaves from city streets may have picked up oils and car exhaust compounds. Heavy metal contamination can come in with industrial wastes, or sewage sludge (biosolids), and unlike pesticides, will not degrade. Class A biosolids are tested for fecal coliform, salmonella, heavy metals and a few chemical contaminants. They can be sold as suitable for garden use, although not on Organic farms.

Some herbicides are digested by grazing animals, some degrade if composted, some bind to the soil. Some plant growth regulator herbicides, however, pass straight through livestock and kill the plants they land on. The list includes clopyralid, aminopyralid, aminocyclopyrachlor and picloram. Manure, compost, straw or commercial organic fertilizer can be contaminated. Organically produced materials should not contain these toxins.

Mushroom compost is pasteurized after the mushrooms are grown, and sold to vegetable growers. The material does not contain the right nutrients to grow a second round of mushrooms, but is useful for vegetables, with an NPK of 1-0.7-1, with a high calcium level.

Compost tea comes in two main kinds: anaerobic and aerobic. The anaerobic method is to put some organic matter in a container of water. Wait at least a few days, then draw off the liquid. Microbes will have decomposed some of the material and released some nutrients. Some people call this type of tea a “watery extract” to distinguish it from aerobic compost tea, which has air bubbled through it until done. To make “tea” you can use finished compost, weeds, comfrey, vermicompost, manure.

Compost tea does have some benefits in the garden, but not as many as some wishful thinkers believe. An increase in plant growth has been shown in studies in comparison with water. Not surprising! No study has shown better results from compost teas than other plant fertilizers with similar amounts of the same nutrients. It’s cheaper for you to make compost tea than buy fertilizer. But it may be better value for your time and money to use the organic matter you would have made into tea, in some other kind of compost.

Does compost tea build healthier soils? It is mostly water, which doesn’t build soil. The solid matter left behind might improve soil structure if added directly. The tea does not. Adding microbes via compost teas does not increase the number of microbes in the soil, except very short-term. Microbes will die and feed each other, go forth and multiply until the number of various types have rebalanced, back to the same numbers before your intervention. In a 5-year tree study, compost contained 50% more microbes than compost tea did. Skip the tea-making!

If compost teas are sprayed on foliage, some of the microbes may outcompete some existing microbes, including plant pathogens. Some plant diseases (powdery mildew in some cases) were helped by compost tea. Others (gray mold, downy mildew) seem unaffected. Washington State University has done extensive research. Composts vary, tea-making varies, weather varies. Compost tea is far from a cure-all, that much is clear.

Which composting system suits your conditions best? The trench method works for gardens with no space for bins or piles. Eco-enzyme and compost tea are small scale activities. Vermicomposting and Bokashi can be done indoors in winter. A chart compares traditional composting, vermicomposting and Bokashi Ferment, and another chart compares six traditional compost methods.

If your compost is high carbon, with lots of visible leafy or woody particles, spread it on the surface. If dug in, it would need to find plenty of nitrogen to continue decomposing the carbon. If your compost is still “hot”, and not fully mature, don’t dig it in, as it could hurt your plants.

Robert Pavlis tackles the issue of using too much compost, leading to problems with very high phosphorus levels in the soil, by recommending 1” (2.5 cm) of compost a year as a sustainable amount. Commercial compost may contain an NPK ratio of 1-1-1, whereas plants use 3-1-2. Homemade plant-based compost might have an NPK of 3-0.5-1.5. If you use compost to supply all the P the plants need, you will need to supply more N. This is safer than using compost as your main source of N, and building up too much P in the soil.

Excess phosphate gets locked up in the soil, and it could make it hard for your plants to absorb iron and manganese. If this happens you may see interveinal chlorosis. Some crops are good at integrating and removing phosphorus from the soil, so the situation can improve over time, if you minimize the P you are adding each year. If you see no excess phosphate problems, I advocate for not worrying too much! Expect to get some of the nitrogen you need from cover crops, and added fertilizer.

As well as your preferences and conditions, environmental concerns are important to consider. How much carbon is lost as CO2 or as methane? How much nitrogen is lost? If you didn’t compost, what would your alternative be? Would that produce more or less greenhouse gas? Sending organic matter to the landfill is the worst option. In general, the more aerobic your compost process is, the better for the environment. Bokashi and vermicomposting only take the material halfway to being composted. Remember that producing your own compost helps your garden soil and crops, and your wallet.

Robert Pavlis has a new book Microbe Science for Gardeners, coming soon.

Book Review: Worm Farmer’s Handbook


Rhonda Sherman: The Worm Farmer’s Handbook: Mid- to Large-Scale Vermicomposting for Farms, Businesses, Municipalities, Schools and Institutions,

Chelsea Green, 2018, 247 pages, $29.95

 The Worm Farmer’s Handbook is exactly that. It explains very clearly how to farm worms on food scraps, manure, yard waste, paper and more. It goes beyond the “tub under the kitchen counter” scale of worm bin, upwards to commercial farming and community-scale enterprises. Rhonda Sherman is an excellent writer, inspiring, concise, personable, candid and very down-to-earth. Art and science. Detail without fluff. For beginners and upgraders.

The book includes the many reasons you might venture into vermiculture (worm production) or vermicomposting (worm cast production); earthworm biology; business plans; equipment set-ups; bedding and stocking rates; feeds and feeding methods; monitoring for success; harvest and post-harvest practices; and over two dozen global case studies, including some in places I bet you didn’t think of: Turkey, Afghanistan, and an air force base in Ohio. Some highly successful business people got some of their boost from worm farming.

Rhonda Sherman started as a recycling consultant, producing a much-scorned-at-the-time factsheet Worms Can Recycle Your Garbage, which became immensely popular. Answering the demand, she created the annual NC State Vermiculture Conference, the only one of its kind in the world. In 2000 she established the NC State Compost Learning Lab, with 26 kinds of composting and vermicomposting bins and space for hands-on teaching. So, she has full credentials to tell us about how to produce vermicast for profit or manage waste produced on farms and gardens, in municipalities, industries and institutions.

A tour of the Worm Barn at the NC State Compost Learning Lab

First, to clarify the terminology: vermiculture is the raising of worms for bait or animal feed or for selling to other worm farmers; vermicomposting is the conversion of organic wastes into worm castings (vermicast), a nutrient-rich, microbially active soil amendment or growth medium for young plants. The word vermicompost is sometimes used to refer to a mixture of castings, uneaten bedding and feedstock (organic material). To avoid confusion between compost (a thermophilic aerobic process) and vermicompost (a warm-not-hot mesophilic process involving the material passing through earthworms), Rhonda uses the word vermicast.

Nowadays the main reason for worm farming is to process organic wastes and use the vermicast to grow stronger, more nutrient-dense food crops or marijuana. It is possible to keep costs low, even fairly large-scale, by manufacturing your own worm bins and by screening the vermicast manually, or with a small motorized sifter. Additional income can come from selling vermicast tea and teaching classes.

Vermicast sells at a much higher price than regular compost, 7-60 times more! The microbial populations in vermicast are much larger and more diverse than those in thermophilic compost. Seeds germinate more quickly in vermicast-amended soil, the seedlings grow faster, the root mass is much bigger, leading to earlier, bigger yields. Strangely, and proven scientifically, all these improvements are independent of the nutrients available to the plants. The turnip photo is astounding. Crops with vermicast-amended soil have greater resistance to insect pests, because the vermicast adds phenolic compounds to the plants, making them distasteful to bugs (but apparently not to humans!). Plant parasitic nematodes (such as the root knot nematode Meloidogyne hapla) can also be suppressed.


The earthworm biology chapter is fascinating. Rhonda opens by saying “I don’t want to put you to sleep with a long-winded discussion of the anatomy and physiology of earthworms.” No danger of that. This is concise, technical and yet easy reading. Who knew there are species of earthworms that reach lengths of 3ft (91 cm), 4ft (1.2 m), 4.5ft (1.4 m), 6ft (1.8 m), 13ft (4 m) and an eye-watering 22ft (6.7 m). Only the smallest two of those are in the US, and no, not in Virginia! Some earthworms don’t live underground in the soil – the epigeic group live in the leaf litter. Seven species of worms are suitable for vermicomposting, and Eisenia fetida, the red wiggler, is by far the most widely used.

To start a worm bin, buy at least 1lb (0.5 kg) of these worms per square foot (0.09 m2) of surface area. That’s much denser than I imagined. And don’t go to the bait shop, because you’d have to buy dozens of packages for every pound of worms, throw out all the containers, and pay $122-$225. From a reputable worm grower you will pay $20-50 per pound, perhaps with added shipping.

Rhonda walks us through all the necessary steps of preparing to farm worms. Study the state and local regulations, and the safety issues, and make a business plan before buying worms, except perhaps for a small pilot scheme. Don’t expand before you know how you will make it work. Production and marketing are equally vital. Will your state regard this as a composting process (lots of regulations) or a livestock farming enterprise? Plan to avoid the problems and have contingency plans in case they happen anyway.

Photo NC State

In designing your physical set-up, there are options from small outdoor pits or bins to continuous flow-through bins. Buy or build your own, after studying the pros and cons. Look for suitable readymade containers at a good price, such as Macrobins and IBC totes used for vegetable and other storage and transport. Source your feedstocks and decide if it would be best to pre-compost them before offering to your worms – often wise if dealing with large deliveries of food waste, to reduce volume and pest problems. This book helps with information on the space you’ll need for all stages of the process. Plan ahead. Imagine yourself 10, 20 years older when delivering feedstock, monitoring your livestock and emptying your bins. Don’t build things too wide, tall or heavy. Leave access space all around your bins (unless very narrow). Imagine more climate change.

Don’t geek out too much on the equipment though – remember you are farming livestock and will need to prioritize learning their ways. You need a 6″ (15 cm) layer of moist bedding, a layer of worms at a sufficient density for the container, a thin 1-1.5″ (2.5-3.8 cm) layer of feedstock and a covering layer, so the worms can eat without being exposed to the light. Enough air and water, light to prevent them crawling away. Wait till they’ve eaten all you’ve provided before adding more food, or you will get fruit flies, gnats, flies, ants etc. Rhonda advises on various feedstocks. Check at least once a day, to make sure your worms are healthy, thriving and mot crawling out of your bin. As needed each day, water the top of the bin, using a mist or light fine spray.

Worm farming can fit with other types of farming with good results. Livestock manure (except poultry manure) is a good feedstock for worms. You can experiment with adding some worms to a composting toilet. Vegetable, fruit and flower crops can provide crop residues; food processing has what would otherwise be waste; shredded paper is good (the ink on printed paper is not toxic nowadays, but avoid glossy paper and fancy papers with metallic additions).

A worm bin is not a trash disposal – you need to find a recipe that combines your ingredients in the right proportions to provide a balance of nutrients. The ideal starting ratio is 25 carbon:1 nitrogen, and a helpful list is in the book. You can use an online compost calculator to roughly determine an appropriate mix. Pre-composting is a good way to turn your materials into a homogenous substance the worms will thrive on. This avoids the problem described by Rhonda as “the worms beeline for the melons and stay away from the onions.” Rhonda provides ten reasons for pre-composting.


Earthworm husbandry is central to worm farming. Inspect daily with eyes and nose, and squeeze a handful of bedding to test for moisture. Never pour water directly into the bin “even if you have seen people do it on YouTube!” as Rhonda cautions. Once a week count population samples at 4″ (10 cm) deep. Take 6″ (15 cm) squares, count and record worm numbers and make sure numbers don’t go down. Keep your worms in a temperature range of 60-80F (16-27C), cooling, insulating or heating as needed. Adding extra feed will help raise the temperature in cold weather, but don’t overdo it. Add cow patties and see if your worms choose to congregate there. Add an insulating layer and watch out for other animals (“with sharp teeth!”) sheltering there. Be aware that too much cooked food can attract different types of flies.


Six worm bins.
Photo NCSU

The instructions for harvesting worms, vermicompost or both are very practical. For small-scale enterprises with limited budgets there is the table harvesting method – spreading the top layer of the bin material on a table and hand-sorting worms, vermicompost and unconsumed food. This is made more efficient by using bright lights to cause the worms to cluster in the middle of the pile, avoiding the light. Another method, if you only want the worms, is to add fresh feed in a wide mesh tray on the top of the bed, after fasting the worms for a week. When the worms gather in the tray, scoop them up.

To harvest vermicompost, you can make screening boxes. Sort the finest vermicompost for sale or use on the farm, and return the coarser material and the worm cocoons to the bin. Return the worms to the bed or sell them. A way to harvest the vermiculture but not the worms is sideways separation. Set up a new bedding and feeding area adjacent to the old one, after not feeding the worms for a week or so. They will gradually move sideways into the better accommodation and you can harvest the vermicast from the old area. Continuous flow-through bins allow vermiculture harvest without disturbing the worms. This involves grates in the bottom of the bin and a way of scraping the vermicompost across the grate. This was the only place in the book where I do not understand the description, and there was no helpful diagram or photo. Fortunately a description later cleared up the mystery.

There is a good photo of a homemade trommel (cylindrical screen) involving bicycle rims. Worm farmers are definitely a hands-on crowd! Packaging and shipping can involve egg trays cut to size on a band saw, and breathable bags sewn from rolls of rowcover.

Vermicast can be tested using compost-testing criteria, and the book tells you the target values for pH and various elements and also the acceptable pathogen limits. There’s also a list of 13 bragging points which you can include on your label if selling your products. There is also a warning about what not to claim on you labels!

Rhonda Sherman

The last chapter of the book consists of 27 diverse global case studies, and makes inspiring and confidence-building reading. So many ideas you could use for your own worm farm! Rhonda points out that she herself is operating from a small research station, with a small staff. Sites profiled include the Len Foote Hike Inn (Georgia), a state park facility where you do indeed need to hike in. The facility was built in 1998 to be sustainable. The worm bins are fed guest meal scraps, shredded office paper, cardboard, discarded natural fiber clothes and even cotton mopheads! The Evergreen State College collaborates with Cedar Creek Corrections Center in Washington to recycle their food waste. The prisoners designed and built the equipment, saving the taxpayers $2000 per year and reducing the facility’s water consumption by 25%. The vermicompost is used in the prisoners’ garden to grow vegetables for the facility.

The Medical University of South Carolina reduced food waste with worms and has recorded the data in good academic fashion, providing everyone with some precise information on quantities, labor requirements, expenditure and productivity. Wright-Patterson Air Force Base (Ohio) began vermicomposting when they acquired a bin and a quarter-million earthworms from another air force base where they were no longer welcome. With one hour of labor per day, the staff were able to save $25/day hauling waste food and provide vermicompost for the base golf course (hey, better than chemical fertilizer!)


Various school projects are acclaimed for educating children and getting them onboard with reducing landfill lunch components by 85%, in one case. After lunch, the SCRAP carts (Separate, Compost, Reduce and Protect) carts (operated by students, staff and custodians) are wheeled around to collect up whatever has not been eaten.

The Green Organic Agricultural Production Company in Kabul, Afghanistan, is a woman-owned business with the goal of composting and vermicomposting 20% of Kabul’s organic waste, and train other women in the process. They use open-air beds built of concrete blocks, producing 100 tons of vermicompost annually.

The diversity of the farms profiled is a real help in showing the process as manageable on various scales, in various climates and with varying degrees of funding and mechanization. Perhaps the widest range is the feedstocks: everything from manures and vegetable wastes to agave bagasse at a tequila production plant, waste from a palm oil extractor plant. And scales up to 200,000 tons per day (maybe bigger). Reading these profiles will also steer you away from repeating mistakes already made by others, such as the large continuous flow-through bin made of wood, that fell apart under the strain, dumping worms and vermicompost on a concrete floor in the middle of winter in Michigan.

Corrugated cardboard is a surprising source of nitrogen – it’s in the glue. As paper is recycled, the fibers get shorter each time until they are too short to be useful for recycling (this is why egg boxes and apple trays are not recyclable. Worm farming is the perfect use for these products, and worms are partial to paper sludge.

There are five pages of Resources, nine pages of Bibliography and a twelve page Index. That’s an impressive index. Twin Oaks runs an indexing business, and I have written two books myself, so I have a fine appreciation of indexes!