Dec 032012
 

by Avis Licht  

Erosion caused by overgrazing of cattle 

I’m sitting in my office, looking out the window at the pouring rain.  A huge winter storm has descended on us.  For the water we are grateful. We just need to make sure that it  doesn’t all run off  and erode our precious soil. Erosion of topsoil is one of those strangely ignored problems that can create huge problems, but can be addressed with straightforward solutions.

In their book, Topsoil and Civilization, Vernon Carter and Tom Dale, make the convincing case that our misuse of topsoil is directly related to the downfall of civilizations. It takes 500 years to form 1 inch of topsoil and with unsafe soil practices this important layer can be washed away in minutes. They write, “Civilized man was nearly always able to become master of his environment temporarily.  His chief troubles came from delusions that his temporary mastership was permanent.  He thought of himself as “master of the world” while failing to understand fully the laws of nature.”

Topsoil supports life.  Through thousands of years topsoil was formed as organic matter decayed and was deposited in layers.  For 350 million years the quality and quantity of soil and life increased. With the advent of civilized man, soil building processes was reversed in most places.

A tiny fragment of the land area on the earth represents the soil that we depend on for the world’s food supply.  This small fragment competes with all the other needs – housing, cities, schools, land fills, etc. It is up to each one of  us to take care of, protect and enhance our own topsoil.

THINGS YOU CAN DO TO PROTECT YOUR SOIL:

1. Plant to cover your soil. In vegetable gardens use cover crops in the winter where you don’t have vegetables growing.

Plants cover concrete wall

Once the plants are in you can barely see the retaining wall

2. Judicious use of wood and stone to form retaining walls can make a big difference in stopping erosion.

Stone for raised beds

Raised beds using stone for both low and tall walls

3. Create ditches and/or swales to slow and redirect water runoff.

Swale, at the top of the hill, redirects runoff, and is also covered with biodegradable fabric that has seed sown in it.

Check out these photographs of  waterfalls in my own garden after 10 inches of rain!

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Nov 082011
 
Low retaining walls can help prevent erosion

Low stone retaining walls keep soil from falling into the driveway

Erosion of  hillsides can range from minor movement that is easy to repair, to major and dangerous situations.

Caveat! Caveat! Caveat!

If you think you have a major problem, please refer to a professional soil engineer or contractor to help you.  In this post, I am only going to address simple  erosion problems.

 

 

 

 

Building low stone retaining walls can be simple and effective for keeping  hillsides from eroding.

These walls were built without mortar in  a method called drystack.  Only soil was used to hold them in place.  Cutting back into the hillside, laying the stone, back filling with soil and then planting keeps the base of the wall stable.

Loose soil will collect in the beds at the bottom of the hill.

Vegetated swale

The swale is covered with a biodegradable erosion blanket and sowed with clover and wildflower seeds

 

When assessing your slope for erosion problems look for these signs:

  • Channels already formed in the hillside from runoff
  • Bare soil that is exposed to  rain or water runoff
  • Downspouts or other water sources

Ways to minimize water damage include:

  • Create swales that are on the contour of your slope
  • Build retaining walls that have drainage in them
  • Sow seed and plant  fast growing shrubs to cover bare soil
  • Mulch, mulch, mulch

 

Wild strawberry and Mahonia with stone wall

At the top of the stone wall you can see the wild strawberry (click to enlarge)

In the photo above I planted a native strawberry that sends out many runners and roots into the hillside.  It will cover the hill very quickly. Other California native plants that provide excellent cover are creeping Ceanothus, trailing Manzanita and  Sonoma Sage and Coastal Sage Brush.

Planting on steep hills

Creeping ceanothus, trailing manzanita and other natives were used on this steep shady slope

Small stone walls

Small walls at the base of trees keep soil and mulch in place

The most important action for you to take in your garden is OBSERVATION.  Go out in the rain and storms and watch how the water flows.  This is the best way to learn about your garden and the only way to really know what is happening.

 

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