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Interview with author Robert Pavlis

Author Robert Pavlis

Today's author interview featuring our winning giveaway question is with Robert Pavlis, the author of Soil Science for Gardeners: Working with Nature to Build Soil Health.

Soil Science for Gardeners is an easy-to-read, practical guide to the science behind a healthy soil ecosystem and thriving plants. The book debunks common myths, explains soil science basics, and provides the reader with the knowledge to create a personalized soil fertility improvement program for better plants.

Be sure to enter our next giveaway which begins March 19th on Facebook and Instagram for your chance to win a copy of Keeping Bees with a Smile: Principles and Practice of Natural Beekeeping.

What is the rhizosphere and why is it important to plants?

The rhizosphere is a very thin layer that surrounds the roots. It’s important because this layer affects the plant much more than the rest of the soil. For example, the pH of the soil might be 7.5, which is not ideal for plants, but at the same time the pH of the rhizosphere might have a pH of 6, which is perfect for most plants. Plants actually condition the pH of the rhizosphere.

The rhizosphere is concentrated with microbes. Some of these are very beneficial for plants and in fact, plants excrete chemicals into the soil to attract the right kind of microbe to the roots.

Understanding the rhizosphere gives you great insight into the value of both microbes and organic matter, for plant growth.

What is the biggest myth about fertilizers?

The myth that plants need to be fed leads to all kinds of poor advice for gardeners. You don’t fertilize to feed plants. You fertilize to replace the missing nutrients in soil. This means that nobody can tell you which fertilizer to use, unless you have done a soil test.

It also means that there is no such thing as tomato fertilizer, or orchid fertilizer or any other plant specific fertilizer. All of the online suggestions about which fertilizer NPK ratio to use for a particular plant are incorrect, because the author of those recommendations knows nothing about your soil.

When you fertilize, add the nutrients that are missing from the soil. This does not change with the types of plants you are growing.

What happens to organic matter once it is added to soil?

It slowly decomposes. Even so called “finished compost” will continue to decompose for another 5 years, or so. Large molecules are slowly decomposed into smaller and smaller molecules, by the action of microbes, until it is converted to CO2, water, humus (carbon) and nutrients. These nutrients are then available for plants.

The value of organic matter is this slow release of nutrients and the remaining humus. The nutrients feed plants and microbes, and the humus builds soil aggregation, which is critical for root growth.

Can you add too much compost to your soil?

Definitely. Compost adds nutrients to soil and these nutrients are identical to the nutrients in synthetic fertilizer. Too much fertilizer or too much compost can result in toxic levels of nutrients.

An inch or two, added as a mulch is good in most soils. More can lead to problems.


Winning Giveaway Question's

What are the top 5 reasons I should be paying attention to soil science when I'm growing vegetables instead of just winging it and amending with compost every year?

About 10 years ago I was asked to develop a 12 hour beginner gardening course by the local university. The course was designed for home gardeners, not university students. I checked several large standard gardening books in my own library. A 700 page one had not a single page on soil. Another of about 650 pages had 3 pages near the back of the book. That makes no sense. After many years of gardening I learned one thing. Plants need soil to grow.

Once you have healthy soil, you can grow any plant that is suitable for your climate and soil conditions. Gardening is all about providing healthy soil.

I understand that new gardeners want to learn about plants - the sexy part of gardening. Experienced gardeners want to understand the soil because they have come to realize that gardening success is all about the soil, not the plants.

I designed the course so that the first night of about 2.5 hours was all about the soil. The following weeks were about plants?

That is not really 5 reasons, but one big one.

  • Adding fertilizer when you don't need it is a waste of money, a waste of our natural resources and it harms the environment.
  • Adding too much organic material can result in toxic soil where nothing grows well.
  • You can't fix a problem you don't understand

I have been rehabilitating a neglected garden for the past few years. What are the most important amendments I should be making to my soil? Would I benefit from having it tested

Without knowing the current condition of your soil, nobody, including me can advise you on what to do next. In the book Soil Science for Gardeners I take you through a process to test and understand your soil. Then I help you create a customized soil improvement plan.

I assume by testing soil you mean a lab test. You can do several other types of soil tests yourself, and these are described in the book. Would you benefit from a lab test? How are things growing now? If things are growing OK, then it is unlikely you have a nutrient deficiency, or toxic levels of nutrients, and then a lab test is not of much value. If you are having trouble growing things, then a test will show you if you have a nutrient problem, and it will tell you how to fix the problem


Robert Pavlis

Robert Pavlis has been an avid gardener for over four decades. He is the owner and developer of Aspen Grove Gardens, a 6-acre botanical garden that features over 3,000 varieties of plants. Specializing in soil science, he has been an instructor for Landscape Ontario and is a garden blogger, writer, and chemist. The author of Building Natural Ponds, Pavlis is a well-known speaker whose audiences include Master Gardener groups, horticultural societies, orchid societies, and garden shows such as Canada Blooms and the FarmSmart conference. He teaches gardening fundamentals at the University of Guelph and garden design for the City of Guelph, Ontario, where he currently resides.

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