Book Review: Soil Science for Gardeners, by Robert Pavlis

Book Review: Soil Science for Gardeners, by Robert Pavlis, New Society Publishers, 2020. 228 pages, with charts and diagrams, $18.99.

I recommend this book to all gardeners who have hesitated to open a soil science text for fear of dry incomprehensible overloads of numbers. Robert Pavlis explains how your garden grows, and dashes cold water on false myths that may have been wasting your time and limiting your success for years! He leads us to a better understanding, including on a microscopic level, of soil biology, chemistry, physics, geology and ecology and to a place of wonder and curiosity at the everyday functioning of crops and soils.

This new comprehension can lead us to do right by our plants and our gardens, leading to healthier plants and higher yields. Robert writes in plain language, as a gardener with over 45 years of experience. He is the author of those Garden Myths books you might have seen. Perhaps, like me, you paid them little attention, thinking your own knowledge was fact-based. Even so, like me, you might find you had been holding onto some anti-facts (mine was that I believed compost is acidic – not so!). This book aims to have us understand real soil and make real improvements, via a Soil Health Action Plan at the end of the book.

The three sections of the book are Understanding Soil, Solving Soil Problems, and A Personalized Plan for Healthy Soil. A satisfying, logical sequence. Read the sections in the order presented! Robert says it’s very easy to grow plants if you understand the soil which anchors them, feeds them and provides the air and water they need to survive. With a solid understanding of what’s going on, you won’t need to memorize rules.

The 2016 definition of soil, by the Soil Science Academy of America is “Soil is the top layer of the Earth’s surface that generally consists of loose rock and mineral particles mixed with dead organic matter.” A rather bland underselling of what soil accomplishes. Here comes myth-bust #1: “Soil is not alive. It does not need to eat or breathe.” “The whole idea that soil is a living organism that requires similar attention to animals is completely false and leads to many poor recommendations for managing soil.” No, don’t give up here! It’s not the soil but the ecosystem of the soil and all the living organisms in and on it that holds the life. The ecosystem contains life, but is not itself alive.

Air and water are critical for good plant growth, about 25% of each. A simple, startling truth. The sand, silt and clay we might worry about make up another 45%, and 5% organic matter might fill out the total. A large tree can remove up to 100 gallons (400 liters) of water a day, discharging most of it into the air as water vapor. As the water leaves the soil, air is pulled in to fill the spaces. Roots pull the oxygen in, day and night, to convert sugars into energy. Were you also lead to believe that plants photosynthesized by day and respired only by night?

Did you know (I hadn’t thought about it) that “soil pH” is really an average of the pH of the water in the soil, and a spot with organic matter and lots of bacterial activity will have a very different pH from a spot with less organic matter? The rhizosphere (the area right around a plant’s roots) can have a very different pH from the soil solution further away. Plants can grow in alkaline soil because their roots are actually growing in acidic conditions. The nitrogen-fixing bacteria on legume roots cause the plant to release hydrogen ions, making the rhizosphere more acidic. To some extent, our efforts to change the soil pH can be undone by our crops and weeds! A soil property called buffer capacity lets the soil absorb materials at different pH and maintain its same level. Peat moss is acidic, but it does not acidify alkaline soil. The soil in the rhizosphere can be 2 pH units different from the soil around. This is usually written about in rather magical terms, but here it is in plain language.

Roots grow just fine where there is enough phosphorus. Adding more at transplanting doesn’t help, and can hinder. Visual plant symptoms can predict possible deficiencies, but are not a reliable diagnosis. Purple leaves may indicate phosphorus deficiency or cold temperatures, high light intensity, pest damage or lack of water. Or a nitrogen shortage reducing the plant’s ability to absorb phosphorus. There’s much that we don’t know!

Pay attention to the Cation Exchange Capacity – the measure of the soil’s ability to hold cations – because many plant nutrients are cations. You can increase the CEC by increasing the clay content, increasing the OM or increasing the pH. Read more in this book.

Have you ever thought about the “free” nitrogen from legume root nodules? Rethink of it as “homegrown” or “solar” rather than simply magic and free, because the leguminous plant may use up to 20% of the sugars produced during photosynthesis, to feed the bacteria.

Don’t justify your adherence to organic gardening by falsely claiming that synthetic fertilizers kill bacteria. Bacteria feed on both synthetic and organic fertilizers. This book challenges us to find the factual basis for choosing to grow organically, making us stronger advocates.

Hoophouse bed broadforked to aerate the soil without inverting.
Photo Pam Dawling

The bacteria chapter is followed by a chapter on fungi. Fungal spores are everywhere, even the Antarctic. Fungi are crucial for cleaning up plant litter on the soil surface. They grow above-ground hyphae which can penetrate dry leaves or wood chips and move the nutrients deep into the soil. Bacteria can’t tackle such tough stuff! 150 species of fungi capture and digest nematodes.

Why is organic matter important?  This chapter explores the chemical and biological effects of organic matter on soil. Soil contains three forms of organic carbon: the living (15%), the dead and the very dead (stable humus and charcoal). Increasing the level of organic matter in the soil can increase aggregation, improve water infiltration (reducing runoff), increase aeration, increase water-holding capacity, improve tilth of clay soils, reduce crusting, and improve the size and distribution of the pore spaces. Those are just the physical effects. It will also increase the cation exchange capacity, increase the availability of nitrogen, boron, molybdenum, phosphorus and sulfur, and increase the microbial activity and diversity.

Often we think about adding partially decomposed OM such as compost and manure. We should face the reality that compost tends to have low levels of nutrients (maybe 1:1:1).   The big value of these is in providing food for microbes, short-lived beings that provide a constant supply of fresh OM, multiplying its value. Partially decomposed compost takes about five years to finish decomposing, during which time it slowly releases nutrients. This gradual steady supply is what crops need. The humus left at the end is a complex molecular mixture of carbon, hydrogen and oxygen, resistant to further decay.

The initial effect of adding fresh OM (not composted OM) is an explosion of microbial reproduction, feeding and death. The microbes use nitrogen, which can cause plants to suffer a shortage. It takes time for a new balance to be achieved, providing adequate N for the plants.  The needs for the N can encourage gardeners to add so much compost that the P level is too high, which can bring death to mycorrhizal fungi, leading to roots driving deeper to access their own P from the soil directly. We have very high soil P, a result of misunderstanding soil test limits. I have worried about it, then read more and stopped worrying. Soil P is pretty stable. If you are not leaching P into a waterway, it just stays in your soil until a plant need it. We switched to using less compost and more cover crops where we could. We were already using a lot of cover crops – it’s not like we were slouches in that department! After more time, I settled on accepting our situation, and as the plants show no sign of P-caused problems and our soil is bursting with earthworms, it doesn’t affect us much.

I mentioned at the beginning that I learned that finished compost is alkaline, not acidic. In the initial composting stage, acidity happens. Then fungi thrive, and decompose the tough lignin and cellulose, causing the pH to rise and bacteria to take over. Compost-making has lots of myths! Poorly understood science makes them grow, I suppose. Bokashi composting, for example (more of a fermentation than a composting process) is based on the idea that fermented material decomposes faster, although it’s unclear if this is really true. “The best method of composting is the one that you do and continue to do because you like doing it. Any form of composting is better than taking yard waste to the curb.”

The Rhizosphere chapter is fascinating! Root exudates can restrict the growth of competing roots, attract microbes into symbiotic relationships, Change the chemical and physical properties of the soil solution and the soil, and make nutrients more available. Bacteria make explosive population growth as they feed on exudates. Then their predators, nematodes and protozoa, join the party. The soil water around the roots becomes a nutrient soup. By photosynthesis, the plants produce the attractive exudates that the soil food web turns into plant nutrients right where the roots can efficiently hoover them up. Plants are active in seeking nutrients, not passive recipients. Not to say they have knowledge, or think and plan. It’s a matter of chemical reactions controlled by enzymes with the capacity to change their activity based on the presence or absence of chemical triggers. Let’s marvel at the reality! We don’t need fairy stories!

The second section of the book, Solving Soil Problems, starts with identifying the problems, and works through techniques affecting the soil, chemical and microbe issues, increasing organic matter and structural problems. We are not feeding plants, we are replacing missing nutrients in the soil, so they can take the nutrients they need. The solution will depend on your soil, so a “tomato fertilizer” is not going to be what tomatoes need in every soil. If you plan to top up the missing nutrients, get a soil test to learn what those are. But if you plan to apply manure or compost everywhere as your only amendment, your money is wasted on a soil test. If you add compost every year and return cover crops, organic mulch and your plant debris to the soil, and your plants are mostly growing well, you probably don’t need to add any other fertilizer to your garden. This alarmed me a bit. What about boron shortage, which happens here? Yes, if you are a farmer or market gardener, yields do matter and soil tests (free for commercial growers in Virginia) will be worthwhile. But for a home gardener, or a landscape gardener, yields might not be at the top of your list. Robert explains various tests, and gives his take on how useful they are. The information here can save a lot of confusion and wasted effort.

Photo by NCSU Crop Soil Undergrad course

In the techniques chapter, the author explains the dramatic difference in available nitrogen in a cultivated garden and a no-till one. No-till can supply up to five times the nitrogen, because tilling adds more air into the soil, increasing the microbial activity, burning up the OM. There is a useful chart comparing the effects of fertilizer, compost and wood chips on the soil. We’ve all learned not to bury wood chips in the soil, where they use up the nitrogen while decomposing. But on the surface they can do wonders.

Crop rotation has come under scorn recently from commercial growers who are focused on maximizing yield and profit for their time on small areas of land. Sure, salad mix and baby spinach can rake in the money. But generations of farmers have learned to grow different types of crops each year in a particular spot. This can increase yields 10-25%, even though we are not sure why. Studies have shown it’s not simply nutrient availability. It could be pH changes freeing up more nutrients, or microbe biodiversity, or differing root growth granting access to more depth than the current crop alone can achieve. Rotated crops are more drought resistant and make better use of nitrogen. Research is needed.

As I was happily digesting this book I was brought short by this mnemonic that still puzzles me: “If you have trouble remembering whether P stands for phosphorus or potassium, remember that these nutrients are listed in alphabetical order. Phosphorus comes before potassium in the alphabet, and so P comes before K.” Um, K comes before P, last time I looked. Confusing.

Does rock dust add nutrients? No evidence, says Robert. Do not be beguiled by mineral products claiming to add 74 minerals to your soil. Plants might only use 20 of them. More is not better! Beware fad products such as biostimulants and probiotics. Plants cannot use vitamin B1. What about compost tea? Yes, it adds nutrients, but claims that the included microbes work wonders are not supported by science: test results are very mixed, including worse. Sometimes we are too gullible! Milk, molasses: they add nutrients but no special magic. Fermenting something cannot add nutrients – it could make some more available, although that isn’t proven either. The fungal and bacterial populations increase, but are the species nutritious ones or pathogenic ones?

Photo by Soil 1

The gardener’s goal is to farm healthy microbes, even though they are too small to see. Use the state of the soil and the health of the plants as indicators of the health of the microbes. Supply OM, water and you’re on the right track. It has been proved useful to add rhizobium legume inoculant if you haven’t grown legumes for some years. Fungal inoculation of soybeans in low phosphorus soil will be effective. Not otherwise.

The author’s general practice is to improve the soil environment to help existing microbes. There is a list of 7 general ways to do that. There is a whole chapter on increasing OM, using what’s local and cheap. Coir is a waste product, but its production causes environmental damage to local water supplies (large amounts of sodium have to be leached out).

Biochar, one of the new “Garden Wonders”, has claims to make big improvements to the soil food web. Most of the biochar studies have been conducted in labs, not on farms. Even then, 50% of the studies report higher yields, 20% report no change, and 30% report a decrease. There are probably better ways to spend your money!

What about gypsum? I believed the common advice to use it to break up clay soils. Mostly this myth is not supported by evidence. Gypsum can have some negative effects. Add more OM instead. Likewise for improving sandy soils: add more OM.

The final section of the book is a set of worksheets and instructions to help gardeners improve the soil health where they are. This is a slow process, so start soon! Robert has also made the forms available on his website First assess your soil, then make an action plan, then record your progress.

I recommend this book for all sustainable/regenerative/organic gardeners and small-scale farmers, and even large-scale farmers who realize there are gaps in their understanding of soil science. This book is very accessible, user-friendly and full of soil-based common sense. Winter is a good time to make new plans!

Robert Pavlis has two websites: and as well as a YouTube channel

What’s growing in the hoophouse; reading; planning for winter.

Tokyo Bekana in the hoophouse.
Photo Pam Dawling

In the hoophouse we are perhaps half way through our bed preparations. The Tokyo Bekana was the first crop we transplanted from our outdoor nursery bed, and it’s looking very sturdy now.  We’ve also transplanted some Yukina Savoy and the first of the lettuces.

Cherry Belle radishes in the hoophouse, early October.
Photo Pam Dawling.

The crops we direct sowed in early September are growing well, and we are harvesting the radishes and some of the tatsoi and Bulls Blood beet greens (thinning to 6″ apart). The spinach is big enough to start harvesting but we haven’t needed to yet.

Hoophouse tatsoi in early October.
Photo Pam Dawling

The newer sowings (the second radishes and the first brassica baby salad mix (mustards) have emerged and are ready to thin to 1″. Sometimes we use thinned seedlings as a salad garnish, but it takes more time than simply pulling them out, and it takes attention to keep them clean.

This summer we grew more cover crops rather than seed crops, which we have been growing in summer for several years, because we were short of workers. In the photo below you can see some healthy cowpeas I’m going to be pulling up later today, as well as some pulled up and dried buckwheat. We don’t dig our cover crops under, just let them die on the surface for as long as possible, shedding bits of dead leaf, then haul them to the compost pile. With the cowpeas, we hope to leave the nitrogen nodules from the roots, by ripping the plants up roughly!

Iron and Clay cowpeas as cover crop in the hoophouse.
Photo Pam Dawling

These cowpeas have been cut back two or three times over the summer, to keep them manageable. At one point, they were black with sooty mold growing on aphid honeydew. We wondered if it was going to be a bigger problem, but after we cut the plants back, most of the aphids seem to have died. We also got a healthy population of ladybugs.

December beds with row cover.
Photo Wren Vile

I gather readers are planning for winter, as many folks have been visiting my Winter-Kill Temperatures List of hardy crops. I update this list every spring, with the info from the previous winter. It’s useful for planning harvests based on forecast temperatures, and it’s useful for planning which winter crops will grow in your location, either inside or out.

On the same theme, I just discovered the WeatherSpark website which provides “The Typical Weather Anywhere on Earth”. Enter your nearest town or airport and you get clearly explained info with fascinating graphics of how the weather goes over the year in your locality. Note this is not a forecast site, it’s about average weather for each place. Useful to people who’ve recently moved and want to know what to expect this winter, or to new gardeners who haven’t paid so much attention previously. Or to those who want to check their assumptions (I really thought the wind was out of the west more of the time than records say). There are charts of high and low temperature, temperature by the hour each month, cloud cover, daily chance of precipitation (both rainfall and snowfall), hours of daylight, humidity, wind speed and direction and solar energy. A big help in making wise decisions. I know that climate change is going to cause havoc with averages, and we’ll need to learn to become better weather forecasters individually, and to use soil temperature and other metrics to decide when to plant. But this website explains things well.

Tomato seed strained in a sieve.
Photo Pam Dawling

I wrote a more concise description of saving tomato seed for the Mother Earth News Organic Gardening blog. For the full length version, see my two posts here and here.

The October Growing for Market is out. Flower farmer Erin Benzakein writes about getting to grips with the marketing side of running a farm. She encourages farmers to get good photos, step out from behind the camera, and dust off their website. I could use some of this advice! (I’ve been very busy writing a hoophouse book, and have necessarily paid less attention to giving presentations and to rejuvenating this website!

Kai Hoffman-Krull writes about on-farm trials of bio-char. I’m looking forward to reading that. Jesse Frost writes about winter CSAs and profiles some he visited. Chris Bodnar covers Italy’s thriving agricultural co-ops and asks if this could be a model for the next phase of the locally-grown movement. Lastly Zach Loeks offers the first of a two-part series on Transitioning to a permaculture market garden.

The September/October issue of Organic Broadcaster is also out. Articles include attending to soil health to improve production; the top reasons customers buy organic foods (accountability, environment, health); interseeding cover crops in cash crops; an interview with farmers in the MOSES Farmer-to-Farmer Mentoring Program; designing an efficient pack shed; and selecting the right meat processor.

Lastly, the campaign has posted a letter a letter recently sent out by farming mentor Eliot Coleman about the travesty of allowing hydroponics to be certified as Organic. Hydroponics is a system of growing plants anchored in holes in plastic tubes, or in blocks of inert material, and feeding them with a liquid solution of things that work to produce mature plants. The arrogance of imagining we know everything a plant needs is astounding! The idea that all the many complex ingredients of soil can be replaced with a synthetic concoction is staggering!

Eliot Coleman’s letter includes these quotes:

Organic farming is best defined by the benefits of growing crops on a biologically active fertile soil.

The importance of fertile soil as the cornerstone of organic farming is under threat. The USDA is allowing soil-less hydroponic vegetables to be sold as certified organic without saying a word about it.

The encouragement of “pseudo-organic” hydroponics is just the latest in a long line of USDA attempts to subvert the non-chemical promise that organic farming has always represented. Without soil, there is no organic farming.


Eliot Coleman will be a speaker, along with Fred Kirschenmann, Enid Wonnacott, Jim Riddle, Will Allen, Jeff Moyer, Dave Chapman, Anaise Beddard, Lisa Stokke, Tom Beddard and  Linley Dixon at the Jacksonville Rally of the Keep the Soil in Organic movement. Oct 31, 2017 at 12:45 pm – 2:00pm EDT. Omni Jacksonville Hotel, 245 Water St, Jacksonville, FL 32202, USAThis Rally will be a gathering of organic farmers and eaters from all over the world. The march will begin at the Omni Jacksonville during the lunch break from 12:45 to 2 PM on Tuesday, the first day of the NOSB meeting. There will be a 5 minute march to The Landing from the Omni. Lunch will be available at the Rally. For more information, call Dave Chapman at 802-299-7737.

Review of the Organic Broadcaster, and Bug Tracks

Photo courtesy of Organic Broadcaster and MOSES
Photo courtesy of Organic Broadcaster and MOSES

Maybe you are not getting a chance for any agricultural summer reading, but I’ve been lucky enough to have some time off, while the crew took care of everything. I recently discovered the Organic Broadcaster, newspaper of MOSES, the Midwest Organic and Sustainable Education Service. This magazine is a free digital or print bi-monthly. You can subscribe here.  You can also make a donation or post an ad, which will help the paper stay afloat.

Although I don’t live in the Midwest, I really appreciate this publication. It’s an 11 x 17″ 24-page newspaper, with a board of directors drawn from Minnesota, Missouri, Iowa, Illinois and Wisconsin. Unlike many East Coast organic publications, this one includes information from farmers growing grains and raising livestock.

The articles are in-depth and substantial, and there are also news briefs, classified ads and an events calendar. The display ads are from businesses relevant to sustainable farming.

The July/August issue is packed with at least 12 articles. It includes (what I think are) regular pages: Ask a MOSES Expert (this time: setting a reasonable rent for grazing land); Book Review (this time The Small Scale Dairy by Gianaclis Caldwell); news from the Rural Women’s Project.

In the summer issue, the other articles included: Non-GMO farmers caught in the crossfire on herbicide-resistant weeds; Financial analysis showing the demand for grass-fed beef is growing; Discussion on the Organic status of hydroponically-grown crops; Using heat generated by a composting process to heat tanks of water and using that stored heat for  hoophouse (high tunnel) beds through a cold snap; Seven lessons in farm diversification; Research exploring the benefits of using cover crop mixes; Marketing your farm brand; Collaborative Farming (new farmers helping each other at Sandbox Co-operative, a 50 acre incubator farm – see them on You Tube); Prevention and sustainable controls for external parasites of livestock; Keeping useful farm records; and a study comparing soil health under organic and non-organic systems.

The News Briefs section contains info on field days, MOSES book sales, and sales of audio recordings from the previous MOSES conference, links to useful organizations, legal guides, funding and resources. Altogether a very valuable resource.


Bug Tracks blog
Bug Tracks blog

Another discovery while I indulged in summer gardening reading was the blog Bug Tracks. It has the subtitle Bringing glory to Earth’s small and neglected creatures. Charley Eiseman writes this blog and takes the splendid photos. He is a freelance naturalist based in western Massachusetts.If you have a mystery insect, you can send him a photo to see if he can identify it. Or you can look at pictures  of bugs that have mystified him, and see if you can identify those, if you’re very good! He has a Monthly Mystery series.

We’ve just had National Moth Week, and Charley’s current post has pictures of moths.

book_cover_awardCharley Eiseman has also written a book, Tracks & Signs of Insects. “The first-ever reference to the sign left by insects and other North American invertebrates includes descriptions and almost 1,000 color photos of tracks, egg cases, nests, feeding signs, galls, webs, burrows, and signs of predation.”

He’s now working on another book, this one on North American leaf-mining insects.

And I’m back at work, hoeing lettuce and setting up irrigation.