Planting Edmonds: The dirt on garden soil

Planting Edmonds is a monthly column written by and for local gardeners.

“Essentially, all life depends upon the soil … There can be no life without soil and no soil without life; they have evolved together.”  —  Charles Kellogg, USDA Yearbook of Agriculture, 1938

It’s almost summer, and gardening season is in full swing. As we plant up pots of flowers, watch vegetable seeds promising tasty food and nurture our trees and shrubs, we notice the most important part of our garden – the soil. Avid gardeners love the look, feel, and smell of good soil. Let’s talk some more about this foundation of our gardens.

Notice how I said soil, not dirt. Soil is the complex miraculous medium that supports plant growth. Calling it dirt raises the hackles of horticulturists and soil scientists, though that stuff you wash off your hands after gardening definitely seems like dirt.

My garden soil, not dirt!

Plants were on this planet long before animals. They developed a highly successful collaboration with the very thin top layer of our Earth and prospered. In the process, over time, plants made Earth hospitable for animals and eventually us, the pinnacles of evolution, the My Edmonds News reader!

Let’s start with what plants in general need to survive, then how soil meets those needs, the characteristics of soil and finally, a bit about soil amending.

First, shelter. Unlike animals, plants shelter-in-place. They stay where they are and make it work. To do this, they need some sort of anchor to the ground, something to keep them from washing or blowing away. They need water and they need it to come to them. They also need food.

Plants make their own sugars using solar energy — something they needed to figure out before animals could come along and eat them to supply their own energy. They also need minerals. Plants need nitrogen, phosphorus, potassium, calcium, magnesium, sulfur and more to help source the vast diversity of chemistry needed to make them work. Finally, plants — like all living things — need oxygen, a gas.

That is a lot of requirements for our needy plants. Let’s take a quick look at what makes up soil and how it meets those plant needs.

Soil has three main components: mineral, organic and biotic. The mineral or inorganic fraction is a mixture of sand, silt and clay, physically distinguished by size. Sand is bigger than silt, which is bigger than clay. This medium is something the roots can grow into to anchor plants in place. It is also the source of the minerals they need. The spaces between particles contain the oxygen plant roots need.

The organic fraction called humus is mainly the decomposed remainder of plants and animals. This fraction is important for retaining water and supporting the biotic component.

The biotic component is the vast and complex network of living organisms making their home in soil – bacteria, fungi, worms moles, etc.  Just as we are becoming increasingly aware and appreciative of ecosystems above ground, the same holds true for the soil ecosystem.

Just one example is a group of beneficial soil fungi called mycorrhizae. They form interactions with plant roots that enhance plant growth. Like our new appreciation for the role of bacteria in our gut for human health, we are also learning how important these fungi are for overall plant health.

Soil is a complex ecosystem that has co-evolved with plants to provide them with everything they need – support, water, minerals and oxygen – except sugars. They can make those themselves from the above ground leaves we know and love.

Enough background. Let’s talk about gardening.

When you read anything about garden soil from any source, the authors always tell you to test your soil. Find out what its texture is, how well it drains, what its pH is and what are the nutrient levels.

As an enthusiastic gardener and retired scientist, I have always felt compelled to follow these marching orders. I have gardened since I was a child in Spokane. Over a lifetime of gardening experiences, how many times before last weekend do you think I have tested my soil? None, nada, zilch, zippo. Despite good intentions, I did not test the soil.

But being asked to write a gardening column on soil, I felt compelled to test some soil. It’s now or never. So, I did, last weekend, just in time for this column.

A percolation test assesses how well your soil drains water. You want those air gaps left behind to supply the oxygen. I dug a hole, filled it with water twice, and measured how fast the water level went down after the second fill. A reference I was using said that water receding at 2 inches over two hours is “adequate drainage.”

My water was already down more than 2 inches by the time I came back to check after turning off the water! All was gone within 50 minutes. I have great drainage. Most planting instructions say to plant into well-drained soil. Mine is a rock star (no pun intended). No problem getting oxygen to my garden plant roots. Next, the type of soil.


All the water drained from my garden hole in less than an hour!

All soil references talk about knowing what type of soil you have, using a vocabulary that reminds me of conversations at a wine tasting: “It is nice sandy loam with a hint of clay and subtle undertones of earthworm dung.” I used two methods to test my garden soil type: the jar method and the ribbon method.

First, the jar method. I collected soil, shook it up with water, added a little borax (helps clay particles settle), and waited 48 hours. It slowly settled into distinct layers of sand, silt, and clay. I measured the height of each layer, calculated the percentage and used a USDA handy-dandy chart to classify my soil. Mine was right between a loamy sand and sandy loam.

The ribbon method was way faster but somewhat disconcerting to a data geek like me. I moistened my soil to form a ball, squeezed it between my thumb and forefinger, and tried to make a ribbon. Based on how long a ribbon you can make before it breaks, you get your soil classification. Easy-peasy and fast. My soil formed a ball, but could not be pressed into a ribbon, so it came out “loamy sand.” Same basic answer as with the jar test, but way faster.

My soil forms a ball and not a ribbon – it’s a loamy sand!

OK, I’ve got fast-draining loamy sand soil. What’s next? All garden references say to collect your soil samples and send them to a lab for expert analysis. I didn’t; not enough time before this column’s deadline, but I did have an unopened soil-testing kit from a local nursery that I received as a gift several years ago. It measures soil pH, nitrogen, phosphorus and potassium. I used that. Crunch time!

Soil pH is a measure of its acidity. This is important because soil acidity determines how available certain nutrients are to your plants. Plants evolved in their native soils to extract the nutrients they need optimally at the pH of soil they evolved in. In Western Washington, most of our soils are acidic (low pH) because the abundant rain leaches out more alkaline (high pH) minerals. Many of our favorite garden plants here thrive in acidic soils — rhododendrons, camellias, hydrangeas, ferns and blueberries to name a few.

My soil tested to a pH between 5.5 and 6, or “acidic.” No big surprise. This is probably a typical soil pH for our area’s gardens.

I measured the “big three” of plant nutrients: nitrogen, phosphorus, and potassium. After some fun with chemistry, my soil scored a 0 out 5 — or “depleted” – for all three major nutrients. Bummer. And my soil was doing so well up until now.

My soil is low nitrogen, low potash (potassium), low phosphorus and acidic.

So, I have a well-drained acidic loamy soil with low fertility. What do I do about it? Now that I have some street cred on soil testing, let’s talk about amending garden soil.

To amend or not to amend, that is the question. The guidance used to always be to amend. Add peat moss or other soil conditioners. But we have learned that if you plant shrubs and trees in the same soil you removed from the hole, the roots will grow into the surrounding soil instead of staying in the restricted area of amended soil.

For a whole bed, we used to cultivate – dig it all up, turn it over, amend and plant. Now, not so much. If your soil already supports plant life, you want to leave that ecosystem as unperturbed as possible. Farmers are doing this too. More and more are using “no-till” farming practices to protect their precious soil instead of the older practice of plowing it all up every year.

But what if your soil is sandy with low fertility like mine? You can go with the gardening hand you’ve been dealt. Grow things that can tolerate this type of soil. Improve your soil over time by adding a thick layer of relatively coarse mulch. This will suppress weeds, allow gas exchange between air and soil, conserve moisture and slowly add organic matter to your soil.

A relatively coarse organic mulch protects this garden soil

Some of this mulch is abundant and free! Leaves that accumulate in your yard are a source of natural mulch for your garden. When I lived in St. Louis, with every fall came the big chore of raking and bagging all the leaves that fell from the four large maple and two large sweetgum trees.

When I moved to Edmonds, our new house was surrounded by bigleaf maples. I braced myself for the annual leaf removal chore. But wait! My wife brought to my attention an article in The Seattle Times that pointed out that it is better to rake your leaves into the garden beds and just leave them there. Easier and better for the ecosystem? I was sold. The leaves decay over time, nourishing the soil and providing winter cover for bugs and other critters. One of my new pleasures in this leaves-in-place routine is watching the varied thrushes turn over leaves looking for bugs to eat.

Fallen leaves are good for your garden.

Some situations call for amending the soil. Most of us are not living on lots with pristine, undisturbed native soil. If you are putting a garden into newly disturbed soil, then a good soil analysis followed by prescribed amendments will start the healing process and make your soil hospitable to plants.

Some garden plants need alkaline soil — asparagus, spinach, cacti and succulents, for example. Increasing the pH of most of our soils in this area with lime helps with lawns, fruit trees and vegetable gardens.

What am I going to do about my soil, you ask? I am going to play the long game. For the new perennials and shrubs I plan to put in it, I will probably add a little starter, water the first year and then use the power of mulch to slowly increase the organic material it currently lacks.

It’s time to get back out into our gardens. We have seeds to sow, plants to plant, and shrubs and trees to nurture. Let’s take a moment to appreciate the wonder of our garden soil, a critical and complex ecosystem supporting all the bounty and beauty we see above.

For me, after my soil-testing experience, when I come inside from gardening to wash the dirt off my hands, I will say “There goes acidic, nutrient-deficient loamy sand — down the drain.” Happy gardening!

— By Joel Ream

Joel Ream grew up in Spokane and earned a Bachelor of Science in botany at the University of Washington and a Master’s in botany at Michigan State University. Joel spent 37 years as a plant biologist at Monsanto, using plant physiology, biochemistry, and analytics to increase the efficiency of crop production. He also worked on new weed control technologies, regulatory studies to support the safety of new products, greenhouse and field evaluation of new crop varieties, increasing the nutritional value of animal feed, and developing methods to measure grain composition. Joel retired to Edmonds in 2018.

  1. Nothing but huge applause for this interesting, informative, and timely article. Many thanks for this effort.

  2. Thanks very much for your fact-filled article. Given your expertise, I hope that you can answer a question for me. Lately, every bag of garden or potting soil I have purchased contains a large proportion of beauty bark, including numerous small twigs. Why is this mulch now being added to commercial bagged soil? I can’t help thinking my young plants and freshly planted seeds would do better with more soil and less mulch. Am I mistaken? Please let me know your thoughts on this subject.

    1. Hi Diana. I have noticed the same thing. I can’t speak for the “why”, but I agree that less mulch in potting soil would probably be better.

  3. Is there any benefit to sending soil samples to a lab for testing? I am new to Edmonds and hoping to garden on new-to-me land with a 1960’s era house.

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