Book Review Plant Science for Gardeners by Robert Pavlis

Cover of Plant Science for Gardeners

Plant Science for Gardeners: Essentials for Growing Better Plants, Robert Pavlis, New Society Publishers, June 2022. 224 pages, 6” x 9”, photos, drawings, diagrams. $22.99.

This is a valuable, concise, accessible book for home gardeners, homesteaders, market gardeners, small-scale and large-scale crop farmers. As I noted about Robert Pavlis’s first book in this series: Soil Science: “I recommend this book to all gardeners who have hesitated to open a soil science text for fear of dry, incomprehensible overloads of numbers.” The same is true of Plant Science. Robert Pavlis is a very good science writer. He disentangles false myths from facts, and teaches us how to make science-based decisions and grow healthier, more productive plants. I reviewed Soil Science for Gardeners, in 2020. As well Plant Science, he has a newer book: Compost Science for Gardeners, and coming soon, Microbe Science for Gardeners.

By understanding the science, we will better able to base our decisions on actual conditions, even as those conditions change in the climate chaos we are now dealing with. Our one-time rule “plant garlic in the third week of October” has gone by the wayside as the soil stays warmer later. We now plant garlic around the end of the first week of November. The author has a blog, called, that has had over 14 million visitors and discusses hundreds of garden myths.

After introducing Plant Basics, we get a tour of roots, stems, leaves, flowers, fruits and seeds, and then the whole plant. Woody plants have their own chapter, as do environmental factors, selecting seeds, vegetative reproduction, and plant names. Each chapter includes sidebars exploding common gardening myths (six in the roots chapter!) and tips for assessing plant problems and finding solutions.

After absorbing this book, you will avoid wasting money on faddish garden products and techniques. You can marvel at the information that plant roots excrete chemicals to attract beneficial microbes which then ward off root pathogens.

You can fill any gaps in your knowledge of the xylem and phloem systems for transporting water and nutrients around the plant; and what actually happens during photosynthesis, when the energy of light converts carbon dioxide into sugars and oxygen. When the sun goes down, photosynthesis stops, but roots continue to absorb water and nutrients, and the plant continues to grow and form flowers and leaves.

The awe-inspiring photo of root hairs makes it obvious that they increase the surface area of the roots by an order of magnitude. In this chapter you can also learn to distinguish between fibrous roots (lettuce), taproots (carrots), tuberous roots (sweet potatoes) and adventitious roots (growing out of the stem or leaves, such as on tomatoes).

Roots need a pH between 5.5 and 7.0; temperature between 40°F (4°C) and 90°F (32°C); easy access to nutrients, provided the levels do not become toxic; sufficient air and water.

Learn the real truth about soil mycorrhizal fungi – buying them is a waste of money! Learn about nitrogen-fixing bacteria (both free-living, and symbiotic bacteria in nodules on roots of legumes and certain other plants). The bacteria do not provide “free” nitrogen, but exchange it for photosynthetic compounds made by the plants. Annual plants excrete 40% of their photosynthates and other plants typically provide around 30%. Some of these exudates attract mycorrhizal fungi.

Some plants excrete 50% of the fixed carbon from photosynthesis through their roots into the soil, where microbes feed on them and die, after producing more microbes. The dead microbes provide lots of nutrients in the “soup” around the roots. Some of these nutrients can boost plant growth; some attract nitrogen-fixing bacteria; some inhibit the development of pest nematodes. Plants attract and herd the right microbe food sources towards their roots; they also change the pH around the roots, making insoluble minerals more available. They produce fewer sugars when they no longer need as many microbes. This is amazing plant chemistry in action. It is not a sign that plants are “intelligent” in our usual meaning of the word.

The chapter on stems will help you distinguish herbaceous and woody stems; vascular bundles of phloem and xylem; nodes and internodes; trichomes (stem hairs, scales or spines); terminal and lateral buds.

Rhizomes are not roots, but fleshy, modified stems growing laterally in the soil. Terminal buds develop along the rhizomes at the nodes, and then shoot upwards. When a rhizome is broken up, each piece can become an independent plant. Stolons (runners) are also a type of modified stem, growing horizontally on the soil surface, rather than underground. The baby plants are clones of the mother plant and can be separated to replant elsewhere.

Strawberry plants in their second year. Runners from mother plants create new baby plants. Photo Kathryn Simmons

Vines may curl clockwise or counter-clockwise, despite myths that abound. 90% of vines curl anti-clockwise as viewed from above. Cucumbers can curl either way. Pole beans and runner beans both curl counterclockwise. If you are giving your beans a helping hand, and you are right-handed, you may need to work against your instinct to twine them clockwise.

Leaves have upper and lower epidermis layers, sandwiching the mesophyll and the veins. The epidermis of some plants has extensions such as hairs, that secrete sticky, bad-tasting or smelly substances that can provide a defense against insects and other animals. The mesophyll is where photosynthesis happens. The surfaces of a leaf (especially the lower side) have fairly large openings called stomata. These control the water and air passing out, in response either to the internal state of the cells, or the dryness of the soil.

Pepper plant with aphids and ants farming them.
Photo Pam Dawling

If you are spraying soft-bodied insect pests on your plants, the reason to use insecticidal soap made from potassium salts, rather than detergents like dish “soap” or bar soap (made from sodium salts) is to protect the waxy cuticle on the leaves. Sodium salt soaps and detergents can strip off all the wax coating, leaving the plant more vulnerable to insects.

Hardening off transplants for a couple of weeks before setting them out in the garden gradually acclimates the indoor-grown plants to brighter, windier, hotter or colder outdoor conditions. The leaf cuticle can grow thicker, the stomata smaller or fewer, the plant can grow smaller, tougher leaves. Read this chapter to learn why purple- and red-leaved plants grow slower, and why brassicas can show purple leaf coloration in cold and dry conditions (phosphorus isn’t moving fast enough).

The chapter on flowers provides an introduction to botany for those who have not met the information before, and a refresher to those who have. It includes information about night-length sensitivity (often called day-length sensitivity, although it is the length of the dark period that acts as the trigger to flowering), along with vernalization (a cold period preceding the night-length of the right duration.) In specific situations and climates, flowering may be triggered by strong far-red light, heavy rainfall, or sunlight intensity.

Outdoor lighting in your garden can interfere with blooming triggers. Red light is the most critical. If you have outdoor lights, it’s best to turn them off when you go indoors at night, to enable plants to get enough darkness.

Plants will not have more blooms if you give them extra phosphorus! “All parts of the plant need all the nutrients. An excess of one nutrient, like phosphate, does not make the plant grow better, nor does it cause a plant to bloom more. Don’t waste your money on bloom booster type products”

This chapter is mostly about plants grown for their flowers, rather than as vegetables. As a vegetable grower with a bit of a background in botany, I skimmed this chapter. Many vegetable growers also grow fruit trees or cut flowers, and this book covers all the basics.

The next chapter is about fruit. Fruit protects the developing seed, provides suitable humidity for the seeds, and sometimes provides nutrients for the seeds too. If the taste of the fruit attracts animals to eat the fruit, the seeds might then get dispersed further afield than if the fruit simply dropped near the tree.

Tomato sideshoot – pinch them out or leave them to grow? Photo Wren Vile

Should you sucker tomatoes? See the YouTube video: Suckering is a type of pruning, where side-shoots are pinched out while small. Some gardeners never sucker tomatoes, and deal with the ensuing mass of greenery and fruit. Some prune hard, especially for greenhouse tomatoes, leaving only one main stem. Others take a middle road, and let two or three main stems grow. The author has compiled a table, comparing three degrees of suckering (none, plants sprawled; none, plants in cages; single stem, all suckers removed). What are your tomato-growing goals? Hard suckering reduces the number of potential fruits on each plant, allowing you to plant closer together, increasing your total yield. Suckering also produces an earlier crop, as does any kind of staking, compared to sprawling your tomatoes on the ground. Suckering achieves earliest fruit, tidiness, large fruit, least chance of pests and diseases. These benefits come with the costs of much extra time on maintenance, medium numbers of fruit and lower yield.

The next chapter puts all the plant parts together and looks at the whole plant. While there are features common to all parts of all plants, there are also differences. The author divides plants into four types: annuals, biennials, trees and shrubs. Another difference explained in this chapter is that between determinate and indeterminate growth patterns. Some plants stop growing at some point. Determinate plants grow to a genetically pre-programmed size, then stop getting bigger. Most deciduous trees are determinate – each species has a maximum height.

Indeterminate plants are not genetically limited in size. They may be environmentally limited: tomato plants die with the frost. Some indeterminate plants (some evergreen trees) do continue growing, but the rate of growth slows to perhaps ¼” (6 mm) per year, an amount you might not notice. Determinate vegetable types (of peas, beans, cucumbers and tomatoes) are often called “bush types.” Despite labels, there are not determinate and indeterminate types of potatoes. This is a myth that I fell for. All potatoes are determinate. Some are faster-maturing than others.

Early September photo of hay mulched June-planted potatoes. They’re all determinates!
Photo Kathryn Simmons

Some plants go “dormant,” meaning there is no visible activity above ground. They are not truly dormant, as the roots are still active. Fertilize plants when they are actively growing, not when they appear to be dormant. You can’t usually “wake them up”, although you can overcome summer dormancy of grasses to some extent by watering a lot. After the summer solstice, the increasing night length signals deciduous shrubs to start the complex process of shedding leaves and going dormant.

The cycles of water in a plant are fascinating, and well-described. Water travels from the roots up the xylem channels to the leaves. As the leaves transpire (give off water), a suction force pulls water molecules upwards. The surface tension of the water, caused by the shape of the molecules, causes them to stick to each other as chains of magnets do. Once water leaves the xylem, it moves from a place of high water concentration to a place of lower water content, in a process called osmosis. Water flows towards cells that have less water.

A third water movement process is called guttation. You’ve probably seen it as beads of water hanging on the edges of leaves, in times of high humidity, such as early morning. The roots have absorbed too much water and sent it upwards to leaves that cannot hold any more, and cannot transpire water while the humidity is so high.

Nutrients also move through the xylem from the roots to the rest of the plant. Once at their destination, small, mobile nutrients such as ammonium, potassium, phosphate, and magnesium ions, can move through the phloem cells to other parts of the plant.  Larger molecules, like calcium, iron, manganese, zinc, boron, sulfur, and copper ions, are immobile, showing as color changes in older leaves. Mobile nutrients move out of the leaves in the fall, causing the color changes we see. Plant biology is complicated and there is no simple way to determine which nutrients are deficient in your soil, by looking at the leaves. This is another myth I had bought into, but found surprisingly hard to make use of! One fact is that deficiencies of mobile nutrients show up in the older leaves first, then move to the younger leaves. Deficiencies of immobile nutrients show up in the new growth.

Foliar feeding is widely misunderstood. Nutrients absorbed from foliar sprays enter not via the stomata, but through the transcuticular pores. Heard of those? These are small holes admitting small molecules only, in small quantities. Only 15-20% of nutrients applied to leaves actually get absorbed. Roots are much better at absorbing the large quantities of nutrients plants require.  Save money and get better results, by fertilizing the roots!

Sunflowers turn to face the sun.
Photo Pam Dawling

This book provides explanations of how plants respond to damaged leaves and roots; grow taller; turn to follow the sun (until the seeds are set); and respond to gravity, growing into the typical shape for that plant. When light levels drop (as fall arrives, or after transplanting in shade), plants focus on the more essential root and leaf development, and stop making flowers. Nothing compensates for a shortage of light.

Perennial woody plants are the focus of the next chapter. Many perennial herbs like sage, thyme and lavender are sometimes simply called perennials, masking the secret of good care for them: prune them as shrubs. Learn about the structure of woody stems, the existence of lenticels (openings in the bark) and the differences between softwood and hardwood cuttings. Most trees do not need staking after planting, instructs Robert Pavlis, as he explodes a few more myths. Here are directions for removal of tree branches for best recovery. It doesn’t involve any paint.

Apical dominance is explained, along with a photo of a fruit tree trained flat on a wall, an effect created by managing apical dominance – bending down leaders where you want to create a new branch. Positioning the apical bud lower than the other buds lets the next one back grow out.

Environmental factors are discussed next, including how plants adapt to environmental changes. US winter-hardiness climate zones are explained, along with the limitations of this classification. Dave’s Garden ( is recommended as a reliable site for its classifications of hardiness of various plants. Read about how plants cope with the cold. Soil temperature can make a lot of difference to plant survival. Hence the usefulness of organic mulches (including snow), and of hoophouses. Sugars, fats, proteins and minerals in the cells act as antifreeze and prevent the cell liquids freezing until the air temperature is colder than a mere frost. Buy hardy plants, hardy varieties, give them enough water.

Plants actually have more difficulty acclimating to heat than to cold. Water loss, lower photosynthesis and respiration rates all take a toll. The author explains that plants, animals (including people, I assume), and microorganisms, produce proteins called heat shock proteins, that act as a protective coating around enzymes and nucleic acids. Leaf rolling minimizes exposure to the sun. Hairs on leaves provide some shade (every bit helps!).

Young sweet corn with a sprinkler for overhead watering.
Photo Bridget Aleshire

For new gardeners, figuring out when the soil has dried enough to require watering is one of the hardest things to learn. Push your finger into the soil, and if the soil feels dry, water. Not otherwise. When you do water, water deeply. Shallow watering produces only shallow roots, leaving deeper roots to die. Shallow roots are not drought-resistant.

Climate change is more than warmer average temperatures. It includes increased frequency and severity of droughts, heavy precipitation, strong winds. Plant a diversity of crops, and watch how they do. Consider plants that grow on riverbanks, those that grow in dry places, sites with high elevation and harsh conditions.

Chapter 10 is a guide to understanding and starting seeds. Some seeds are “recalcitrant” (slow to sprout). Once fully mature, some seed can remain dormant for a very long time. Some requires light to break dormancy; some a particular ratio of one plant hormone to another; some need the seed coating to be degraded before germination can happen (walnut trees are a good example); some need fire or a hot temperature (redbud trees). Most vegetables (and 80% of all seeds) are “orthodox” sprouters, and can be stored for that year’s use in paper packets at room temperature. For use in future years, make sure they are mature and dry, then store in an air-tight container under refrigeration. Recalcitrant seeds need different conditions – read the book.

Tomato transplants in pots, ready to plant out in mild weather.
Photo Wren Vile

For starting seeds there are links to a series of five videos covering pots, damp paper towels, and special outdoor winter-sowing methods. In this chapter are pros and cons for each, and tips on which method is best for different situations.

Chapter 11 includes information on plant genetics, heirlooms, hybrids, and GMO seeds. Unlike me, the author considers GMO seeds a safe way to produce food. Be reassured that GMO vegetable seeds are not available to home gardeners, being sold only in large quantities and requiring the purchaser to sign a contract. White Russet potatoes, and very small amounts of summer squash and zucchini may have reached retail sales. (

See also

Chapter 12 covers vegetative reproduction, which is energetically less demanding on the plant than producing flowers and seeds. The downside is that all plants produced vegetatively are genetically identical. When stolons or rhizomes break, the fragments can grow as separate plants. Bulblets, bulbils, cormels are forms of baby bulbs or corms that can grow into new plants. Gardeners use vegetative methods to increase the numbers of plants for the next season. Layering, stem and root cuttings, leaf cuttings, root division – you can learn these from this book. Be skeptical of homemade “rooting hormones”. Willow water does contain low levels of rooting hormones; small amounts of aspirin, cinnamon, peroxide, may help control fungal or other infections or help root hairs grow. None of aloe vera juice, vitamin C, apple cider vinegar has any scientific evidence whatsoever, so don’t waste your time on these.

Chapter 13 is on plant names, and explains the conventions used when providing Latin botanical names. Conventions for naming hybrids are explained. The distinction between cultivar and variety is made clear. Varieties are naturally occurring in the wild. Cultivars are human-bred, including both hybrids and established open pollinated types. If you develop your own strain, you should give it a unique cultivar name. Don’t reuse a name already in existences, as this is inaccurate and leads to confusion.

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