Thursday, March 11, 2010


Today I would like to talk to you about soil. Not dirt, soil. Dirt is what we track into the house from the garden. Soil is a dynamic system containing solids (minerals and biota) and pores (filled with gases and liquids) on which we build and in which we grow.

In my graduate class, Applications of Soil Science, our professor asked us to define ‘soil.’ That’s pretty much what I wrote above. A soils graduate student sitting in front of me wrote for 10 minutes (I read a book) and was peeved when the professor called ‘time.’ When the professor gave his definition it was slightly longer than mine and nowhere as long as the grad-student’s.

The professor wanted to make a point. To the general public the definition of soil is simple. And that was what the class was about; using our knowledge of soil science to work with the public regarding soil management.

Alright. Soil is a dynamic system; it is always changing. Containing solids: minerals; sand, silt, and clay; and biota; living and decomposing organic material (plants and animals.) Pores: open spaces between the solids filled with fluids like water; and gases like air, methane, etc. On which we build housing, roadways, etc. In which we grow plants (and we also build in the soil; tunnels, basements, etc.)

What most of us gardeners are concerned about our soil is the amount of sand, silt, and clay; and the pH, potassium, and phosphorus levels. I will discount the nitrogen levels since those are ever-changing as nitrogen in the soil moves from ammonium (NH4+) to nitrates (NO3-) back to ammonium back to nitrates etc. etc. etc. quickly and constantly.

The amount of sand, silt, and clay determines how easily our soil can be worked, how water retentive it is, and what we can grow. Sand is easily recognized by its’ visible size. Everybody knows sand. Silt is recognizable by wetting the soil and rubbing it between your fingers. If you can feel the particles then it is silt. Clay (not the pottery mineral) is slippery when wet.

An aside about clay. Our soil is clay. When it is dry it is as hard as a rock; great cracks form when it is not irrigated during the summer. When it is wet, it is like trying to walk on a slip ‘n slide. The day I ruptured my Achilles tendon; I tripped over the hose with my right foot, slipped in the clay mud with my left foot, falling face first in a mud puddle, and feeling the'window blind roll up’ in my left calf. It was the third time I had to wear a cast in August. Good times.

There are also mixtures of sand, silt, and clay based on the percentages of each found. For the most part, home gardeners just need to know their soil type so they can adjust their growing methods to the soil. Adding two to three inches of compost to your garden every year helps to ameliorate your soil and make growing conditions just right for your plants. If you have more questions about your soil check with your Cooperative Extension Office or the U.S. Geographical Survey web site.

To check for pH, just get a simple pH kit like Luster Leaf 1612 Rapitest pH Soil Tester. Most fruit and vegetable garden plants want to be in the neutral to slightly acid range. Adding compost and nitrogen fertilizer to any soil will reduce the soil’s pH and make it more acid. Just dust on lime (like the dusting of sugar on a sugar cookie) every year if your soil is too acidic. Raising a soil’s pH is a long term project. If you try to move too fast you may very well ruin your soil.

A friend of mine used to dump her wood stove ash on her garden area. After several years, she began to notice the garden was just not producing as well and her plants looked sickly. When the County Extension agent was over to check on their mint fields, she mentioned her garden. The agent was only too happy to look and see what the problem was.
One look and the agent told her the soil was too alkaline. Which was really odd since their farm was on some of the most clay soil around. Clays tend to be acidic. It took her several years of adding sulfur, nitrogen in the form of blood meal and bone meal, and mint compost to get her garden back to a closer to neutral reading. She had to make an ‘ash dump’ on her land. It is just a pit where she dumps her wood stove ash. It is away from her well and where it will not affect their mint crop.

Moral of the story: Moderation in all soil amendments!

To be continued……………..

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