by Steve Turner

All of us who deal with plants – big or small, annual or perennial, flowers or foliage – have one thing in common. Working with the soil in which they grow. It is often the most overlooked aspect of the garden for new gardeners and the most cherished aspect for seasoned gardeners, who have grown to appreciate the value of good soil. It quite simply is the difference between success and failure for many gardens and can be the difference between the pleasure of gardening and the tediousness of work.

Many of you are familiar with terms like soil structure, pH, humus, etc. But what do these terms really mean and how do they effect our efforts to improve or maintain our soil’s fertility?

Let’s start by looking at pH. Most people understand it as whether the soil is acidic (less than 7.0), alkaline (more than 7.0), or neutral (7.0), and that different plants prefer different ranges, but why? In different pH’s, nutrients move at different rates through the soil. The more acidic the soil, the faster the rate. If a plant is acid-loving and is in alkaline soil, it will not get nutrients at a fast enough rate. Fertilizer in this situation would have no effect because it is not a matter of whether the nutrients are present, it is the rate at which they are available to the plant.

Now, if you need to raise or lower the soil pH for a particular plant, you will need to understand cations and how they affect your ability to change the soil. Cations are positive-charged nutrients in the soil. The most common, in order, are calcium, magnesium, potash, sodium and hydrogen. Calcium is the most important nutrient in your soil and its proper balance to all others is vital since it helps regulate the soil’s pH. Here is why. All nutrients either have a positive or negative charge, and in nature the normal flow of electrical charge is from positive to negative. All clay and humus particles carry a negative charge on their surface which attracts desirable and/or undesirable positive-charged nutrients or minerals to them. If in proper balance to calcium, the clay and humus will keep these nutrients loosely held in a soil solution, which means the nutrients are readily available to the plants’ negative-charged root tips. The measurement of this exchange is called the Cation Exchange Capacity or CEC of the soil, and is measured on most soil tests.

CEC is important in determining how easy it will or won’t be to change your soil pH. A high CEC will make it difficult to change. In a poor soil, for example, as soon as you obtain the proper pH, you then increase the CEC by adding organic matter or humus to the soil. This will increase the amount of negative-charged particles in the soil and help “lock in place” the pH by making it more difficult to change. So, if you are preparing a new soil area, your first concern is the pH. It is critical that you make all adjustments to the pH prior to adding organic matter.

While organic matter raises the CEC, salts in the soil are the enemy to proper CEC. All commercial or synthetic fertilizers contain salt; this is how they bind the nutrients together. Every time you add one of these to your soil, you are adding salt, which in turn lowers the CEC. They lower it by using up all the negative-charged particles in the soil and, as a result, the positive-charged nutrients just leach away. This increases the need for more frequent fertilizing, which in turn adds more salts to the soil, and thus begins a vicious circle that many gardeners fall into. This is why the use of organic fertilizers is beneficial. While it is true that plants cannot tell an organic nutrient from a synthetic one, the soil can. The additives in synthetic fertilizers cause problems for the soil as a whole and a lowered CEC is just one of them.

If you have a poor CEC and lots of salts in the soil, then odds are you have compaction also, which limits root growth and the flow of water and air through the soil. This decreases the activity of beneficial soil microbes and increases the activity of pathogens in the soil, which in turn causes diseases and so the vicious circle continues. 

Humus is one of the keys to breaking this cycle. Humus (or “finished compost”) is organic matter that has been broken down by soil microbes as much as possible. These microbes in turn produce ideal nutrient storage for our plants. Humus can hold 3 to 4 times more water and nutrients than clay alone. It helps store water in the soil for drought periods as well as nutrients that plants can readily absorb as they need them. This holding capacity will help reduce the leaching of nutrients out of the soil and lessen the need for additional fertilizers.

Humus also helps reduce soil erosion. For example, an acre of soil with only 1 percent humus can only hold less than 1/2 inch of water; any more rain than that will simply erode the soil. However, if the humus content is increased to 6 percent, that acre will easily hold over two inches of rain in the same soil. For those of you having drainage problems, this is something to consider.

Soil microbes are the keys to producing humus – if they are not present in sufficient numbers, then all organic matter in the soils stays in its original form or takes much longer to break down into humus. It takes many different types of microbes to accomplish this and they do so in a very systematic fashion. To get an idea of how many organisms there are in the soil, at a depth of 1 to 3 inches in good garden soil, there will be on average 9,750,000 types of bacteria, 2,080,000 types of Actinomycetes (organisms classified between bacteria and fungi), 119,000 fungi, and 25,000 algae in a single gram of soil (Microbiology: An Introduction, 4th edition). These numbers drop rapidly as you go deeper in the soil, but remain pretty high until about 18 inches in depth.

If you live in a newer subdivision, most of the beneficial microbes left with the topsoil that was probably scraped off the land before construction started, and the remaining ones were severely reduced by the soil compaction that followed during construction. This is a problem for many gardeners and up until recent times most of the research was focused on nutrients and soil structure alone. In the last 10 to 20 years, the focus has shifted to the beneficial organisms that make up a living soil.

By getting back to soil basics, we can be much more successful in our gardening pursuits by increasing our soil’s fertility. To correct problems we need to focus on the soil as a whole and stop looking for that one “miracle solution” that will supposedly give us healthier plants. The soil is a vastly complex environment. It can be, and often is, damaged in many ways that need different solutions to help correct each of the individual problems. The terms we discussed should help put you on the right track. Start by doing a soil test to determine your soil’s pH and CEC. Then adjust the pH as necessary, add humus to raise the CEC, reduce or eliminate the use of synthetic fertilizers, and fine tune from there. Good luck!

Steve Turner, Certified Arborist, is from Arboricultural Services in Fenton, MI.

by Steve Turner

Spring and fall are both great seasons for planting trees and shrubs. I know you have all read the pamphlets and have probably done it a few times, but it never hurts for a little review. If I had a dollar for all the improperly planted trees I have seen over the years, I would be rich!

First, dig the hole as deep as the root ball and at least twice as wide. Be sure to not dig too deep; a good way to prevent this is to measure the root ball against the shovel handle and check it often when digging. If you do dig too deep, remember to pack the soil firmly under the ball to prevent settling once the plant is in place. This is more important for trees than shrubs. On the other hand, if the hole is not deep enough, keep digging. Don’t make the mistake of planting high and then mounding soil up the root ball, even in clay soils. One exception is a compacted clay subsoil, which can be found in new subdivisions. If you can’t dig deep enough, then add a lot of topsoil around the top of the root ball to make a gradual decline down to the grade level.

After the tree is in the hole, cut and remove as much of the wire cage (if present) as possible. Any part that you can’t remove should be cut and bent down. Untie the twine around the trunk and pull down the burlap. If the burlap is in good condition, push it to the bottom or cut it out. If it is old and roots are growing through, then leave it and make several vertical slices instead. If you are planting potted shrubs, carefully remove them from their pots and make several vertical slices down the root ball. Grab the bottom of the roots and pull them back up like peeling a banana and set them in the hole with the cut sections pointing out. Next, begin to backfill using the same soil that came out of the hole, making sure to break up any large chunks of soil. Stop and firm the soil as you go. Stop about 6 inches from the top and add fertilizer to the remaining fill, preferably either slow release or organic fertilizer that is low in nitrogen. Complete backfilling to grade level.

When planting trees or large shrubs, do not mix soil amendments such as sand, peat, or topsoil to the fill. These work better as top dressings. They actually create a false environment within the planting hole and do not encourage outward growth of the roots. Instead, the roots tend to wind around in the hole, which can eventually lead to girdling roots. Also, drainage can be a problem with dissimilar soils. Water will not move from one soil type to another until the first is completely saturated. This is why it is important to check the soil of the root ball before you buy the plant. Ideally, you should not plant trees grown in sand in clay soils and vice versa. It will only cause problems in the future. Now that the plant is in the ground, water well and keep the soil moist for several weeks, but do not overwater. Before watering, move aside the mulch and feel the soil to verify it isn’t too wet before adding more water. Keep the mulch away from the base of the plant and do not add too much mulch — 3 to 4 inches is fine.