By Wendy Langhans

So just how much rain did we get on Sunday?  Some reports say over seven inches?  But my watering can is eight inches tall and on Monday morning it was full to the brim.  Several of my potted plants were waterlogged – I had to bail them out.  As I bailed, I started thinking – how much water can dirt hold, anyway?

That depends on the dirt.  In order to answer this question, we have to first ask ourselves, what is dirt made of?  According to this Univerisity of Minnesota website, “Soil is made of air, water, mineral particles, organic matter, and organisms.”  Digging deeper (pun intended), we need to understand three basic terms that soil scientists use to describe dirt:  soil texture, soil structure and field capacity.

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Soil texture.  Soil texture is determined by the proporation of three types of minerals, which are classified by size:  grainy sand (0.05 – 2 mm dia.), powdery silt (0.002 – .05 mm dia.) and sticky clay (< 0.002 mm dia.). Here’s a diagram, the Soil Texture Triangle, showing how soils are named according to the relative proportions of each type of mineral.

Soil structure.  James Nardi, author of Life in the Soil, writes, “A complete soil represents the marriage of the mineral or inorganic world with the organic world.”  When mineral particles clump together into aggregates and you add water, air and organic material, the soil developes a structure.  This structure includes voids or holes, which soil scientists refer to as pores.  As the U of M website describes it, “Half of soil is pore space”.

Field Capacity.  Field capacity is defined as “the maximum amount of water that a soil can hold against the pull of gravity”.  When it rains, water infiltrates into the pores of the soil.  Now normally, you would think that the larger the pores, the more water they would hold. Right?

But you would be wrong. That’s because water is held in the pores by the force of surface tension, working against the force of gravity.  And the force of surface tension is greater with small pores.  That’s why finely textured soils, such as silt or clay loams, tend to hold more water.  And soil in our Santa Clarita valley tends to have a higher proportion of clay.

So what is the “field capacity” of my potted plants?  I dunno…but it was obviously exceeded on Sunday.  All this talk about dirt reminds me of a recipe for Oreo Dirt Cake:  grainy crushed oreos, powdery flour and sticky chocolate pudding.  Add the liquid and stir.  But don’t add too much, or you’ll have to clean up the mess.

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Upcoming Outdoor Events:

Saturday, March 12 – Sunday, May 29, SCV Search & Rescue Trail Challenge 2011: 12 Weeks/12 Hikes.  Click here for more information.

Saturday, March 26, 1 – 3 PM, Wildflowers Galore at Towsley Canyon.  Towsley Canyon is the perfect place to see this year’s flower display.  Meet at the front parking lot.  For directions and trail maps, click here.

Saturday & Sunday, April 2 & 3, 9 AM – 5  PM, Volunteer Training at Towsley Canyon.  Have you ever thought about sharing your love of the outdoors with others?  Would you like to volunteer as a host in our visitor center at Towsley Canyon?  Here’s your opportunity to receive basic training in ecology, visitor services, and cultural and natural history of our local area.  For more information, contact Lisa Ann Carrillo at 310-858-7272 x 115.

Trail Maintenance Schedule.  Come join our volunteers as they help maintain our trails.  Contact Steve at machiamist@aol.com for time and place.

Wednesday mornings, March 2, 9, 16, 23, 30.

Saturday mornings, March 12, 26.

For a glimpse of our local flowering plants, check out the Facebook page, “90 Days of Santa Clarita Valley Wildflowers”.

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