decide if you’re sandy or silty? Try this simple test.
If you’ve never heard of soil types,
you may be surprised to learn that soils are typed not by their
mineral content but by their texture—that is, the size
of the soil grains. There are three basic soil types: sand, silt,
and clay. Sand particles (.05–2 mm across) are gritty,
silt particles (.002–.05 mm across) are floury, and clay
particles (smaller than .002 mm) are sticky when wet.
The exact minerals involved don’t
matter for classification—if you have a soil with grains
that are all 1 mm across, it’s called “sand,” no
matter whether the grains are quartz, mica, basalt, or anything
You can get some idea of your soil type
by just grabbing a handful of it and squeezing. If it immediately
crumbles and falls apart, it’s a sandy soil. If it crumbles
slowly, it’s probably a mixed soil—sand, silt, and
clay. If it sticks together in a wad, complete with imprints
of your fingers, then it’s a clay soil.
If you really want to get down
and dirty, you can figure out the exact proportion of sand, silt,
and clay in your soil. Here’s how:
• A clear quart-size jar (such as a
To do and notice
• One teaspoon
water softener (such as Calgon)
stopwatch (or an ordinary watch)
marker or grease pencil
1. Fill the jar 2/3 full of water.
2. Stir in the teaspoon of water softener.
3. Fill the jar almost to the top with the
soil to be tested.
4. Screw on the lid and shake the jar hard
and fast for at least 20 seconds.
5. Set the jar down on a tabletop and start
your stopwatch. After 20 seconds, you’ll see a dark layer
forming at the bottom of the jar. Mark this line with your marker.
This is the sand.
6. Wait two minutes more, then mark a second
line where the next layer has formed. This layer is silt.
7. The third layer—the clay—can
take anywhere from overnight to a week to settle out. When the
water looks clear, you’ll know that all the clay has settled.
You should see three distinct bands in the
settled soil in your jar: sand at the bottom, silt in the middle,
and clay on top. (Any coarse crud on the top of the layers or
floating near the surface is organic matter.) The thickest layer
in your jar determines your soil type. You can measure the thickness
of these bands to calculate the percentage of sand, silt, and
clay in your soil.
Ideal garden soil has some of each type—sand
to help with drainage, silt to boost mineral richness, and clay
to trap moisture and keep nutrients from washing away. Too much
clay in soil means that there are scarcely any air gaps in soil,
which can suffocate plant roots and beneficial microbes alike,
and it also makes for poor drainage. Excessively sandy soils
can drain too well, leaving plants vulnerable to drought
without frequent watering.
The best soils contain about 10%–20%
clay, and roughly equal proportions of silt and sand. A soil
with these optimal proportions is called loam. A good
loam also contains plenty of organic matter (as much as 5%–10%
in rich soils) to supply nutrients.
Oh—you might be wondering why you added
the water softener. Water softeners are deflocculants; they separate
the clumps of soil into their small constituent particles, so that
they can settle by size.