Far Out Flora

DIY Soil Type Testing

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We always knew our soil was sandy…but just how sandy is our dirt?  Here’s a quick DIY soil type test we learned in our UCCE Master Gardeners Training.

Soil test

Scrounge around your house for a large glass jar with a lid and straight sides, tablespoon, calculator, clothes washing detergent (powder is best), and get a soil sample from your garden.our soil from the backyard

You need to test your soil at the root zone, so dig down about 6-8 inches first before taking your soil sample.  Let the soil dry either in the sun…or if you are really antsy…you can pop it in the oven.  Next sift out any large rocks and non decomposed organic material.

sifted out the organic material and rocks

Break down any larger chunks of dirt.  You should have about a cup of broken down, sifted soil.  Depending on your soil type, it should look like something above.added 1/2 cup of soil to 2 cups of water

Because of the size of our glass jar, I used a 1/2 cup of soil to test.mix the soil

Pour into your glass jar 1 part soil, and 4 parts water, e.g. we poured in a 1/2 cup of soil and 2 cups of water.  Next add 1 tablespoon of clothes washing detergent per 2 cups of water, and shake for 5 minutes.  The detergent acts as a surfactant which allows the bonds between the dirt particles to easily break apart…and settle to the bottom of your jar.  add soap and shake

Now wait for 24-48 hours.   Soil is made up of sand, silt, and clay.  The sand will almost immediately settle to the bottom, the silt settles within about 5 minutes.  However, the clay can take 1-2 days to fully settle to the bottom.24 hours later24 hours later, you can see above that, more or less, all the soil has settled to the bottom:  Sand is the bottom layer, Silt is the darker middle layer, and Clay is the light color layer on top.  BTW above, you can barely see our top layer because there’s only a trace of clay in our soil sample.

Here’s where you need to do a little math.  Measure the total of all the layers, then measure each layer separately.  Divide each layer by the total measurement of your settlement.  Example, we measured 3.1 cm of sand…then divided by 4.6 cm Total of all the Layers = 68% Sand.  You get the idea.  Here’s what we got.

Total Sand, Silt, Clay – 4.6 cm

Sand – layer measured 3.1 cm.  Divided by 4.6 cm total = 68% Sand

Silt - layer measured 1.5 cm.  Divided by 4.6 cm total = 32% Sand

Clay – trace =  0%

Soil triangleUsing the Soil Triangle chart, follow the sand arrow at the bottom to the 70.  Now go to the right and follow the silt arrow down to 30.  Where these two lines intersect shows the type of soil we have.  In our case we’re in the bottom right of the triangle…borderline Loamy Sand and Sandy Loam.  Wow…who knew?

all the layers of the soil

So now what’s next?  Well, we can start thinking about better use of our irrigation, fertilizing, amendments, etc…stay tuned.

– Far Out Flora

12 Comments

  1. This was one of my favorite parts of MG training. Great to do with kids when learning about soil composition. (We’re clay loam over here in Oakland, as it turns out.)

  2. Very cool. I know my soil is very hard clay but maybe I’ll have to see just how much clay I have.

  3. God I wish you guys would have been in my MG class…you would have made it so much more fun! Oh and nice work with the gnome, hula dancers and deer. Reminds me of the time I found little plastic hula dancers had replaced the dangling flowers on my Solomon’s Seal…(the husband was playing in the garden again)

  4. Ah very informative guys! Thanks for this. I’m going to do this over the weekend. I’m assuming I should sift out all the seashells in my soil?Being in the Marina, I would be surprised to find any clay. Its all sand and seashells! I will give you a full report!

  5. Wow, what a great post! I’m going to be at the SF Garden show this year with a booth right near the Master Gardeners. Do you plan on being there? Also, I’m doing a blog post on sandy soil right now, I’d love to use some of your pictures if possible.

    • Thanks Anne! I’ll probably be working at Annie’s Annuals booth for a day or two at the SF Garden Show :) Feel free to use any of our pics from flickr for your blog post. We garden in almost pure sand out here next to Ocean Beach. It might be foggy in the summer, but our drainage is perfect, so we can grow all kinds of cool things.

  6. This is great! I never learned this in my MG class. When the snow melts, in a couple of months, I’m trying this on my garden soil. I know it’s clay but it will be interesting to know how much clay.

  7. Pingback: Farm School: Day 2 | Over the Fence Urban Farm

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