Cheyenne Garden Gossip

Gardening on the high plains of southeastern Wyoming


Soil Testing: Preparing the Samples

soil test application

Colorado State University’s soil testing application and instructions

Published April 21, 2013, in the Wyoming Tribune Eagle, “Get the dirt on soil: Maximize your lawn and garden success by finding the exact concoction of nutrients they need—with a little help from CSU.”

By Barb Gorges

You might be used to putting fertilizer on your lawn and in your garden.

But do you really know what nutrients they need and how much?

Yes, the major nutrients, nitrogen, phosphorus and potassium, the three big numbers you see on fertilizer bags, are important.

But the balance may not be right for your soil. You could be adding too much of a good thing.

Besides the fact that you might be wasting your money, consider the bigger picture.

If the concoction of fertilizer has more nitrogen than your lawn needs, the excess washes into the ground water, polluting someone’s future drinking water.

Excess phosphorus washes into local streams and ponds causing algal blooms, possibly suffocating other aquatic life.

Unlike your plants’ other needs of water and light, it’s not always obvious when your plants need more or less food. In extreme cases, you’ll see yellowed leaves or stunted growth in malnourished plants.

And too much nitrogen, for example, could spur the plant into producing an overabundance of leaves but no blossoms—no flowers, no fruit.

To get ahead of these issues before the growing season, you may want to test your soil.

Luckily, sampling is fairly easy. Unlike my Soils 101 class back in college, I don’t have to dig a 5-foot pit to find out what my soil is made of. This time, I only had to send in samples from the top 6 inches of the areas I wanted the lab to examine.

What a soil test tells you

Soil texture will tell you something about its fertility.

Is your soil sandy? If so, water (and dissolved nutrients) will percolate through it quickly.

Is your soil clayey like so much of Cheyenne’s? Water moves through it slowly. The lab can recommend how much water and what rate you should apply it to your garden or lawn.

Testing for electrical conductivity sounds odd, but that’s the way to find out how salty your soil is, which can affect the availability of nutrients to plants. Some soils are naturally salty, but often here they become that way because too much fertilizer has been added over time, or the irrigation water is salty–comparatively speaking.

Knowing a soil’s pH will help you understand how easily some nutrients can be taken up by plants. It will also tell you what plants may not grow well.

The Cheyenne area typically has alkaline soil. That is why soil amendment advice for the acidic soils of the eastern U.S., such as adding lime or wood ash, can be counterproductive here. Acid-loving plants, such as blueberries and rhododendron, will not grow here unless you plant them in a container in which you can acidify the soil.

The percentage of organic matter in your soil should match your garden plans. It is possible to add too much compost or manure for the plants you want to grow.

Get a soil-testing kit

Home testing kits sold in stores are not usually designed for our alkaline soils and also, the information will not be precise enough.

Colorado State University’s Soil, Water and Plant Testing Laboratory in Fort Collins is one of the few remaining labs of this kind at land grant universities. Being in our neighborhood, the folks at the CSU lab will understand our soils better than those farther away.

The standard test costs $31. See the accompanying information on how to get a sampling bottle, directions and submission form.

Follow the directions

Whatever lab you use, follow their directions.

CSU’s indicated that to get a balanced sample, I needed to collect the same amount of soil at each level—I needed to dig a perfect cylinder 6 inches deep. And dig one of these perfect cylinders 5 to 15 times in random places in my garden or lawn.

How do you get a cylinder of soil? The right tool for the job is a soil probe.

I went out to the Laramie County Conservation District office and asked Jim Cochran, district manager, if he had one I could borrow. He did. And you can borrow one, too.

A soil probe is a nifty little tool, a stainless steel pipe about an inch in diameter and three or four feet long, with a crossbar handle. You punch it into the ground 6 inches and pull out your sample, which you then dump out the side vent.

Well, almost. In my vegetable garden I had trouble keeping the soil in the tube until I was ready to dump it in my plastic dishpan. Maybe the soil needed to be just a little moister. I also tried twirling the probe to keep in the dirt.

Twirling didn’t get me more than an inch into one spot in my front lawn, even after making sure I was between blades of grass. I hit solid clay near the house—probably left by the builders 50 years ago. I had to get husband Mark to help. And then, I needed a sharp tool to dig the clay out of the probe.

I decided to sample both the vegetable garden and the front lawn areas. I took enough sub-samples of the lawn to make two cups’ worth and then mixed them together in a dishpan, doing the same in a separate dishpan for the vegetable garden sub-samples.

The directions said to break up clods and remove organic matter. I picked out as many roots as I could, and a few worms. I spread the dirt (excuse me, soil) out in the bottom of the pans and by the next day both samples were dry enough. Don’t use the oven—it will stink up the house and distort your nitrogen readings.

An important part of the testing is filling out the paperwork. The lab wants to know what’s been growing in the tested area, what fertilizers have been used and how much it is irrigated, so they can understand any anomalies they find. They also want to know what you plan to grow so they can make recommendations.

There is no good or bad soil. It just depends on what you want to grow and whether your soil currently is capable.

In a way, my perennial flower bed performs its own suitability exam. I plant a new type of perennial and if it doesn’t thrive–which could be due to incompatible amounts of light and water as well as incompatible soil–I know I should remember that experience and try something else the next year.

But now that I’m growing vegetables, which can deplete the soil, and we have a lawn that isn’t quite thick enough to shade out the dandelions, I’m curious to see what a soil test can tell me.

In next month’s column we’ll look at the soil testing results and find out what they mean.

 Where to get a CSU soil sampling bottle, directions and submission form

**Laramie County Conservation District, 11221 U.S. Hwy 30 (nearly 10 miles east of downtown, west of I-80 Exit 370), 772-2600.

**Laramie County Cooperative Extension, 310 W. 19th, 1st Floor, 633-4383.

**www.soiltestinglab.colostate.edu (put soil sample in Zip-loc-type bag and print and fill out the submission form)

**Soil, Water and Plant Testing Laboratory, Ft. Collins, Colo., 970-491-5061.

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