“If I want to have a happy garden, I must ally myself with my soil; study and help it to the utmost, untiringly. Always, the soil must come first.” - Marion Cran, If I Were Beginning Again
WHAT IS SOIL ANYWAY?
by Karen Schmidt (schmidt[at]acegroup[dot]cc)
Let’s start with the promise that we won’t call our soil “dirt”. Let’s elevated this miraculous stuff to something much higher! Every living thing on this Earth’s land relies, in some way, on soil. Every bit of food we eat began, in some way, with soil. Whether it was the hamburger that came from the cow that ate the grass that grew in the soil or the apple picked from the soil-rooted tree. Soil is the underpinning of all life. No wonders it’s so important that we understand it, take care of it and help it do its work.
Soil is basically a mixture of minerals, organic matter, gases, liquids and a whole menagerie of many organism that, blended together, support plant life. It is a whole ecosystem within itself that plays some very important roles on our planet. Soil provides the necessary material for plant growth, it stores and purifies water, it modifies our atmosphere and it provides a habitat for the critical organisms that not only decompose dead material but create habitat for other living organisms.
Soil makes up a very thin ‘skin’ of the earth and is the end product of millions of years of climate, wind, erosion and plant and animal deposits. It takes thousands of years for the friction of the wind, the grinding of waves against stone, the fracturing of rock by freezing and thawing cycles, to ultimately result in the fine grains of minerals in soil. It takes the upheaval of earthquakes, the debris of slowly moving glaciers, the impact of meteorites, the chemical reactions of rock and water and air, to achieve the rich mixture of minerals that make up soil. It takes endless cycles of plants and animals, living and dying and decomposing to create the organic components in soil and to nurture the organisms that live within that soil. One shovel of soil holds more living things than all the human beings ever born.
Wow! No wonder soil is so important. We should be filled with wonder every time we take up a handful of soil in our gardens, and we should make a new commitment to protect and nourish this life-giving gift.
WHAT ABOUT YOUR OWN GARDEN’S SOIL?
No soil is exactly the same. Scientists have identified more than 70,000 kinds of soil in the United States alone, and each of those types has a wide variety of ingredients that make them even more unique. The soil in different parts of your own garden is different and unique as well. A professional soil test is one of the best ways for you to discover the make-up, deficiencies and excesses of that soil. And since different areas of your yard may have different soils, more than one soil test may be necessary.
Brian Zimmerman of Four Season Nursery says he can tell the make-up of a soil by observing what grows in it. But that has taken him years of experience as a nurseryman ad landscape designer. For the rest of us, a soil test may be necessary to give us those answers. A soil test gives the gardener a range of important information about his or her garden soil. It tells the acidity or pH level, identifies the percentage of both primary nutrients (nitrogen, phosphorus and potassium) and secondary nutrients (sulfur, calcium and magnesium). Some tests also identify minor nutrients such as iron, manganese, copper, zinc, boron, molybdenum and chlorine.
A soil test can tell what percentage of the soil is organic matter. And if the gardener has identified what kinds of plants he or she wants to grow in that soil (i.e. roses, vegetables, apple, trees) the soil test can give the ideal range of each component tested, and recommended soil amendments to achieve that range. So let’s look at a typical soil test and its implications for your garden. Let’s begin with the percentage of organic matter identified by a soil test (my three samples ranged from three percent to five and half percent). If we think about all the different components of our soil, organic matter may very well be the most important. We think of organic matter as the plant and animal residues in our (manure, leaves, grass clippings, etc.). But until they decompose into humus, they are simply organic material. As much as 90 percent of organic material disappears during the composting process. Once broken down by macro and microorganisms in the soil, the remaining organic matter is mineralized, releasing and immobilizing nutrients such as nitrogen, phosphorus and potassium, making it available for plant growth. What also makes organic matter so important is the fact that it serves as a reservoir for nutrients and water in the soil (it’s the ‘bank’ roots can go to when hungry or thirsty). Organic matter also helps to reduce soil compaction and improves water infiltration in the soil.
What About Soil pH?
Soil pH is an indication of the acidity or alkalinity of soil and ranges from extremely acid (less than a pH of 4.5) to very strongly alkaline (greater than 9.1). A neutral pH ranges from 6.6 to 7.3. Your soil’s pH effects how soluble your soil’s minerals are, which in turn affects how available those minerals are to your plants, since nutrients must be dissolved in solution before they can be used by a plant. Most minerals and nutrients are more soluble thus more available in acid soils than in neutral or alkaline soils. Since much of the bedrock in our region is limestone, which is very alkaline, our soils’ pH is often high (my three samples tested at a pH of 7.0 to 7.4). Out well water has a high line content (check out the inside of my tea kettle!), which raises the pH of the soil when I irrigate. The mineral content of the soil itself is made up of a higher percentage of limestone as well. Since roses prefer a pH of 6.0 to 6.9, my soil obviously needed to be amended to bring down the pH, especially in the bed that tested 7.5. The more basic the soil, the less nutrients, such as iron nitrogen and manganese, can be absorbed. That means that I could add these nutrients to my soil, but my roses would have difficulty absorbing and benefiting from them. It’s sort of like trying to eat a pork chop with a straw. The food is there, it just can’t be accessed. The good news is that I was able to bring down the pH by incorporating sphagnum peat moss and some sulfur carefully following the soil specialist’s instructions. The results were evident even the first year, with healthier happier roses.
As we look at our soil samples, many of us who have light sandy soils (that’s probably the majority of here in Northern Michigan) not only have a high pH but a low potassium level. Potassium is highly soluble and leaches or washes out of sandy soil since it drains so quickly. The short term ‘fix’ for potassium deficiency is to add a potassium – specific fertilizer (i.e. potash). The longer term solution is to improve the soil structure by adding lots of well-rotted compost or manure. Potassium is important for the rose garden because it encourages strong growth (it helps the roses form chlorophyll for optima photosynthesis) and good bloom formation and winter hardiness.
Phosphorus is another important nutrient analyzed in soil test. Phosphorus is essential for strong too growth, for the production of flowers and seeds, and for greater resistance to diseases. It also play a role in the production and movement of plant sugars. Since it does not travel far through the soil, phosphorus is often added, in the form of bone meal, fish meal or soft rock phosphate, at the bottom of the planting hole. If the pH of the soil is too high or too low, the plant cannot access phosphorus. Although phosphorus cannot be readily washed out of the soil, it moves with the soil when it washes away into streams and lakes through erosion. This stimulates the growth of algae in those streams and lakes, which causes eutrophication. You can protect your water table by avoiding overuse of phosphorus fertilizer and preventing any erosion on your property. Since all three of my soil sample test show a ‘very high’ phosphorus level, I try to avoid adding any to my soil.
Magnesium and Calcium
Calcium and magnesium are secondary nutrients, but plants require them in quantities similar to phosphorus. Calcium build strong plant cell walls and improves soil structure. Magnesium is a component of the chlorophyll molecule and is essential for photosynthesis.
All plants require sufficient supplies of macronutrients for healthy growth, and nitrogen is a nutrient that is commonly in limited supply. Nitrogen promotes healthy green growth. But availability of nitrogen in the soil varies. The soil microbes that break down organic matter and make nitrogen available (including compost, manure and our own rose society soil amendment) are not active in cool weather, so nitrogen is not released then. In addition because nitrogen is highly mobile (water washes it away from the root zone). It does not remain in the soil for long period and needs to be replaced each year. That’s why annual additions of organic matter and soil amendments are especially important for adequate nitrogen. And don’t forget one of Mother Nature’s favorite tricks — lightning; lightning actually enhances nitrogen in soil. It breaks down nitrogen in the atmosphere, so it can combine with oxygen; the resulting molecules dissolve in rainwater and falls to the ground. Did you know that five to 8 percent of the nitrogen used by plants (or available in the soil) originates in this way? Those booming summer storms not only give us water, but fertilize our roses!
Many soil tests do not give you a nitrogen level reading. That’s due to the high mobility of nitrogen and seasonal fluctuation in nitrogen levels, as mentioned above. A better indicator of the potential of nitrogen in your soil is the level of organic matter in the soil.
Since organic matter is about 50 percent carbon and five percent nitrogen on average, this organic matter figure makes it easy to estimate total nitrogen. My three soil sample came back with an organic matter of level of 3.5, 5.4 and 3.0. An ideal soil is composed of at least five percent organic matter, so I knew that two of my beds needed additional organic matter and a supplement of some fish emulsion, as well as the usual two applications of CCRS soil amendment. But we must also remember that, because nitrogen washes away from our plants’ root zones fairly quickly and moves down into the ground water, we don’t want to have too high of a nitrogen level either, as it becomes a source of water pollution.
Karen Schmidt (schmidt[at]acegroup[dot]cc), ‘What is Soil Anyway?’ March 2014. Rose Rap, Karen Schmidt, ed. Cherry Capital Rose Society.