Earlier this spring (April 22nd), the world celebrated Earth Day. I hope you took time to enjoy some of this year’s Earth Day events in the Saint Louis area!

In Soulard, one can explore a variety of gardens from elegant manicured gardens to small rain gardens, native planting, or colorful eclectic rock gardens. You will also find spaces in need of tender loving care. There are many areas in the neighborhood that have been derelict for years, whether due to bad weather, poor land or a variety of other reasons.

“I can’t grow anything. I kill my plants and I don’t know why!” Do you hear people say that often? Most of the time, the culprit is the soil. We fail to recognize that we seldom ‘kill’ plants—they die from deficient soil due to improper drainage, chemical imbalance, or lack of nutrients.

We live our lives in a world mostly covered with soil, yet we rarely think about it until we want to plant a flower or a tree, or decide to grow our own vegetables. Would you like to avoid the most common gardening obstacles that soil can present? I think we should begin by answering a simple question.

What is soil?

About 95 percent of soil consists of minerals that have been weathered into particles smaller than pebbles and gravel. You’re probably familiar with the terms “sand,” “silt,” and “clay.” Did you know they’re simply names for the different sizes of soil particles? Sand has the largest particles, then silt, and clay’s particles are the smallest. Figure 1 identifies the characteristics of each of the soil types.

In addition to the three types of soil particles, organic matter and humus make up another 3 to 5 percent of soil’s total weight.

Basic Soil Components.png

The soil in your yard is a unique ‘blend’ of these three components (sand, silt and clay).  You may need to adjust your ‘blend’ to suit the specific plants you’d like to grow.

In addition to soil composition, another important soil factor that can impact your garden is the pH of the soil.

What is pH?

It’s the balance between acidity and alkalinity, indicated by a number on a scale from 0 to 14. The strongest acids (like battery acid) would be near 0. The strongest alkaline chemicals (like lye and ammonia) would be near 14. Plant life is possible in the middle of this scale.

To figure out the pH of your garden soil, you can either get your soil tested or you can do it yourself with a soil-testing kit from a local plant center. A professional testing center can provide thorough results, and also specific recommendations for correcting your soil pH.

Acid Loving < 5.5




Hydrangea (blue)






Medium Range 5.5 - 7.0

Apple, Grapes, Pear, Plum

Ash, Birch

Dogwood, Maple

Spruce, Yew


Daffodils, Dahlia

Rose, Tulip, Violet

Tomatoes, Peppers

Alkaline Loving > 7.0

Asparagus, Celery

Spinach, Sweet peas

Arborvitae Black Walnut, Junipers

Lupine, Redbud


Hydrangea (pink)

Morning Glory

Figure 2: pH Preferences of Some Common Plants

It’s wise to not waste your money on plants until you test your soil! Now that we understand soil composition and pH, let’s test our soil to find out what we’ve got, supplement our soil to support the plants we want, and enjoy our new ‘green thumbs’!   

Soil Testing

If you’d like to have your soil professionally tested, here are some things to know to make your test more successful.

  • Dry your samples before you submit them. A great way to do this is to leave soil sit out overnight on a tray lined with newspaper or another paper. If your sample is too wet when brought to the testing center, it will have to go through a drying process before being packaged for shipment.

  • Pull samples from various areas of your lawn or garden, even if they are tilled. One big sample from just one area of the yard or garden will not give you accurate results.

  • Submit at least 2 cups of soil. Usually a filled sandwich bag or quart-size storage bag will suffice.

  • It typically takes 10-14 business days for your results to be returned. If the soil is wet, add a few extra days.

  • Keep in mind that a soil lab is extremely busy between February and June.

A more detailed chemical analysis of your soil sample will include a pH test result.

There are three convenient locations in the Saint Louis area to take your samples. The fee for this service is $25.

Main testing center:

University of Missoury Extension in St Louis County
132 E. Monroe Avenue
Kirkwood, MO 63122
(314) 400-2115
Hours are M-F 8:30 a.m. to 4:30 p.m.

Drop-off points:

Brightside St. Louis
4646 Shenandoah Avenue
St. Louis, MO 63110
(314) 772-4646
Hours are M-F 9:00 a.m. to 4:00 p.m.

Gateway Greening
2211 Washington Avenue
St. Louis, MO 63103
(314) 588-9600
Hours are M-Th. 8:00 a.m. to 3:30 p.m.                                            

Applying Test Results

If you do need to supplement your soil composition (mixture of sand, silt, and clay, or addition of organic material or hummus), simply follow the test results.

To adjust the pH in your soil, it’s usually enough to add peat, lime, sulfur, or other organic material that will raise or lower the ph. An easy way to raise the pH of your soil is to add wood ashes. If you have been burning wood and saving the ashes over the winter, then you have a valuable source of nutrients for your plants—just mix them into the soil before planting, and don’t apply wood ashes around acid-loving plants like blueberries, rhododendrons, azaleas, and hollies.


Gardening can feel like the best job ever, especially when the reward is month after month of beautiful flowers, pollinators and yummy vegetables. A well-planned garden offers a bounty of colorful, tasty rewards for your work.

Eureka! Voilà! You’ll never kill your plants again.

Illustrations and soil descriptions contained in this article are taken from (1) Nathan Brandt, MU Extension/Master Gardener program, and (2) the booklet “Improving Your Soil” by Stu Campbell.