Q: My wife wants me to buy a couple of truck loads of what she calls black dirt, so that we can spread it on the lawn and use it to create flowerbeds. I think it is going to cost too much and we should just plant using what we have now. She says the topsoil the home builder gave us is too thin.
The grass and trees are growing OK. The house is only three years old and that seems too soon to need new dirt. Would it do any good to have new dirt?
A: I don’t want to get into a family feud, but you’re both right up to a point. I would buy as much new black topsoil as I could afford to make it as thick as possible. Let me explain.
The roots of plants grow in soil, of course. Let’s take a look at what the roots need. They require water, minerals and air in the soil. They need a healthy group of bacteria, fungi and many other microorganisms as well as a large population of larger organisms like insects.
The water and air components are related. Large pores allow air and water to infiltrate into the soil. Small pores trap moisture. Imagine a sponge that has large pores for water and air movement but small pores to retain water. If the soil is full of water, it won’t have much air. The water needs to drain out of the large pores so air can enter the soil, but the small pores hold the water.
Different plants need different amounts of water and air in the soil. A shoreline plant requires more water and less air, while a desert plant needs more air and less water. Each plant can tolerate a variety of soil moisture levels for different lengths of time. A shoreline plant may tolerate drying out for months and a desert plant could tolerate flooding for a few days, if it grows on the shoreline of a normally dry streambed.
As the soil moisture and air levels change, so do the populations of the soil organisms. A teaspoon of soil can contain billions of organisms. Many of them break down the soil minerals into chemicals, which dissolve into the water and then move into the plant roots. Some roots have symbiotic relationships with fungi and bacteria that live inside and outside the roots. These organisms help transfer soil minerals into the roots.
A thriving plant needs a large and healthy root system. The more good soil there is, the larger the root system. There will be more water available, so the plants will need to be watered less often, if at all. More good soil means there will be more nutrients available and less fertilizer will be needed. For the trees, a larger, deeper root system will make the tree more stable in high winds. Healthy, strong plants will resist insects and diseases better, meaning less use of pesticides. Strong grass plants means fewer weeds and less herbicide use in the lawn.
The best thing you can do for a healthy, low maintenance landscape is to give it a good thick soil to grow roots. It doesn’t matter where you live — good soil is the foundation to a healthy landscape. Each part of the country has a different soil type. In the middle, there is plenty of “black dirt,” while it is often called “sandy loam” in the South. No matter what the color or what it is called, more is better. Adding compost or other organic matter will make almost any soil better, too.
Your current landscape plants are growing in your thin soil. Are they thriving, or do they need more watering and care because of poor soil? Creating healthy topsoil on an existing lawn is done with a core aerator and by adding organic matter or maybe a little topsoil. The flowerbeds will benefit from the addition of topsoil and organic matter.
On April 20, an interesting video about soil is coming to the Independent Lens TV series on PBS. It is called “DIRT! The Movie.” Soil is a thin layer on the surface of our planet. It is not easy to create, but it is easy to destroy. When large areas are ruined, it is very difficult to farm. Soil is full of life, and when we apply pesticides or compact it, we damage the ability of soil to grow things. Healthy soil is very valuable and it make sense to protect it. This video makes a case for taking care of soil — worldwide and in your own backyard.
E-mail questions to Jeff Rugg, University of Illinois Extension at firstname.lastname@example.org. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.
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