Don't Treat Your Soil Like Dirt

Don't Treat Your Soil Like Dirt

Vegetables and
Annual Flowers

You've probably heard that the ideal garden soil is a rich loam. But what exactly is this?

A rich, loamy soil contains a range of mineral particle sizes -- from microscopic clays to relatively large grains of sand. These particles are bound together into groupings of various sizes called aggregates. Soil composed of these aggregates has lots of pore spaces of various sizes, and these spaces contain water and air. If all the spaces contain water, the soil is waterlogged; few plants can withstand such saturated soils for long, because plant roots also need air.

What type of soil do you have?
1. Squeeze Test. Take a handful of moist soil. Compress it into a ball, then press it between your thumb and index finger and try to form a ribbon. If the soil is crumbly and won’t form a ball, it probably contains a lot of sand. The stickier the soil is, and the longer the ribbon you can form, the more clay the soil contains. Loamy soil will form a ball that crumbles when poked.

Sandy Soil

Clay Soil

Loamy Soil

2. Soil Shake. Fill a large glass jar about two thirds full of water, then add enough soil to almost fill the jar. Shake the jar vigorously, then let it settle for a few days. The larger particles -- gravel and sand -- will settle first, followed by silt-sized particles, and, finally, microscopic clay particles. In fact, the clay may stay suspended in the water for quite some time. Organic matter will float at or just below the surface of the water. By looking at the layers, you can find the approximate ratio of sand to silt to clay in your soil. "Ideal" loamy garden soil contains 40% sand, 40% silt, and 20% clay.

Very sandy soils have excellent drainage, but can drain so quickly that plants suffer from drought. Clay soils, on the other hand, hold water so well they can easily become waterlogged. Loamy soil provides a happy medium, retaining adequate water but draining well.

If you have a loamy soil, congratulations! But if yours is on the sandy or clayey side, don’t despair. (See the sidebars for some tips on improving these soils.)

Sandy Soil Loamy Soil Clay Soil

Soil pH
You're probably aware that some plants, such as rhododendrons and blueberries, prefer acidic soil. Most garden vegetables, on the other hand, prefer a soil that's only slightly acidic. How do you determine your soil’s acidity? Use a soil test kit (or send a sample to a testing lab.)

Soil acidity is measured using the pH scale, which runs from 0 to 14, with a pH of 7 being neutral. The lower the number, the more acidic; the higher the number, the more alkaline. Blueberries and rhododendrons thrive in soil with a pH in the range of 4.0 to 5.2; garden vegetables generally prefer a pH of 6.5 to 6.8.

In general, soils in regions with high rainfall tend to be acidic; this includes much of the eastern part of the U.S. Soils in arid regions tend to be alkaline. This isn't a hard-and-fast rule, however, and soil pH can vary even within a small yard.

You can raise the pH of acidic soils by adding limestone or wood ashes; you can lower pH by adding soil sulfur, peat, or pine needles. Don’t try to change soil pH quickly by adding lots and lots of these materials; this can disrupt soil life. It can take several years of modest additions to alter pH significantly.

Soil pH is one of the most important and most often overlooked factors affecting plant growth.

Organic Matter
People talk a lot about organic matter, but what exactly does the term mean? Technically, the term organic describes substances that contain carbon. For gardeners, it’s best to think of organic matter as any material that was once living, has died, and has decomposed to one degree or another. Organic matter familiar and useful to gardeners includes horse, cow, and other animal manures, straw and hay, grass clippings, vegetable wastes, bark mulch, wood chips, sawdust, and garden debris.

Amazingly, adding organic matter improves both heavy clay and light, sandy soils. In heavy soils organic matter improves drainage; in dry, sandy soils it increases the water-holding capacity.

So should you add these materials whenever you want?  Surprisingly, the answer is no. Always compost materials before adding them to the garden. Otherwise, if you add fresh organic matter to the soil, the decomposition process can temporarily tie up soil nutrients, making them unavailable to plants. We'll go into some details about composting later in the course.

That’s all for this class. In our next class we’ll "put pencil to paper" and plan a sample garden. See you then!

Class 1, Page 1 2 3 4 5 6 7

Copyright 2002, National Gardening Association. All Rights Reserved.
For questions regarding this web site, contact Webmaster







If You Have Clay Soil...

Add finished compost or well-rotted manure any time.

Mulch beds to keep soil from compacting and cracking.

The addition of gypsum can help lighten soil.

Check pH and adjust as necessary.

Create raised beds, especially for plants that need excellent drainage.


If You Have Sandy Soil...

Add finished compost or well-rotted manure any time.

Use grass clippings for mulch

Till in shredded leaves in the fall.

Mulch beds and paths with straw, and till in at the end of the season.

Fertilize throughout the growing season to supply nutrients.

Keep an eye on soil moisture, and water as necessary. Or install drip irrigation.


Gardening Basics
FAQ #4

What’s the difference between lime, limestone, pelleted lime, and dolomitic limestone?






Adding compost is one of the best things you can do for your garden soil. Here, leaves, grass clippings, and vegetable scraps are piled in a homemade wooden compost bin.

Finished compost is dark and crumbly and has a pleasant, earthy aroma.


Today's site banner is by zuzu and is called "Pericallis hybrida"

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.