by Steve Turner
You are ready to start your new landscape project—you have done the planning, researched your plants, and even had a soil test performed to help you make better choices in your plant selection. Your soil test will tell you 4 important things: the type of soil you have (sand, silt or clay), the pH of the soil, what nutrients are present and in what amounts, and the nutrient-holding capacity of the soil.
So now you are ready to begin, right? Well, that depends. Would you buy a house based upon just 4 facts, like size, location, age and style? Or would you want to know a little more, such as condition, extra features, color, floor plan, etc? While the 4 main facts are very important, it is often the other factors that will help determine your decision and your level of satisfaction in the end.
Knowledge equals success in most cases and your soil is no different. The first thing is to know whether you have dirt or soil. Dirt is what’s left after developers scrape off all the good stuff, while soil is alive and is a living, breathing network of millions of organisms working together in their environment.
There are six major types of soil organisms: nematodes, bacteria, fungi, protozoa, earthworms, and arthropods. What types, how many, and in what ratios will tell you how healthy your soil is and what types of plants will grow best in those conditions.
The first test you need to do is simply take a shovel and turn some soil over and look at it. Is there anything moving or any signs of life? Is there organic matter present? How hard was it to dig? Did you have to jump on the shovel or did it go right in? If you can’t answer yes to any of these questions, or you couldn’t even get the shovel in the ground, you have dirt. You need to create soil first, before you plant, to avoid future problems.
Just like us, soil organisms need three things: air, water and food. Build these into your soil, and the organisms will come. Tilling your soil and adding organic matter will accomplish all three at once. You will create more space for air and water, and add food to feed the organisms that make up a healthy soil.
This is a must in new subdivisions. Homeowners should request that landscapers amend the soil by tilling in compost and pay the extra costs to do so, instead of spreading a couple of inches of topsoil on top. They would save themselves money in the long run by avoiding extra water, fertilizer, and pesticides needed to keep a broken soil system running. Add in dead plants, replacements and the wasted time dealing with all of the above and it really starts to add up.
If you have soil without compaction and you have organic matter, but not a lot of soil organisms present, you can increase their numbers by first eliminating pesticides and excessive synthetic fertilizers on the landscape. In their place, use manure, kelp, or fish-based fertilizers, and continue to add organic matter to feed the soil organisms, which, in turn, will feed the plants. The interactions of all these soil organisms are critical to a healthy system and by manipulating the ratios of one or another, can dictate what types of plants will grow best in a particular environment.
The three major types of soil environments are fungi-dominated, bacteria-dominated, or an equal ratio of both. Trees, shrubs and woodland plants do best in fungi-dominated soils, lawns and prairie plants in bacteria-dominated soils, and agricultural plants in a balanced soil.
There are both good and bad types of all these organisms. Some nematodes feed on plants, fungi, bacteria, and even other nematodes. Some fungi feed on plants, nematodes, bacteria, and protozoa. And so on. In a healthy soil, the beneficial organisms will keep the parasitic organisms in check. The key to this is keeping the soil aerated. Compacted or saturated soils with little air cause anaerobic conditions in which the parasitic organisms thrive and the benificials die. If the soil has a foul smell, it is anaerobic.
Give thanks for soil decomposers such as earthworms, sow bugs, centipedes, etc. They are constantly aerating the soil, as they transport organic matter on the surface down into the soil. There, the other soil organisms can further break it down to forms that the roots of plants can absorb. They are the workhorses of the soil and have been tilling the soil long before the plow was invented.
The use of insecticides, fungicides and nemacides kills both the problem organisms and the beneficials, and is often only a temporary solution. This throws the soil out of balance and can create more problems that require more treatments. There are many alternatives available today that work with the natural system to correct the problem. Some examples are nematodes that feed on other nematodes, fungi that attack grubs and fungi that will kill other fungi for many lawn diseases. Often one application of these will last several years in the soil and avoid the need to constantly retreat a problem on a yearly basis.
All in all, after you understand the soil’s natural system, it is often easier to work with it than against it. Familiarizing yourself with it can save you time and money in the long run.
Steve Turner is a Certified Arborist from Arboricultural Services in Oakland County, Michigan.