Soil Testing: It's a good thing

Posted by: Alison O'Connor, horticulture agent, Larimer County

Spring is coming and gardeners are itchy to get outside and start planting. You've received seed catalogs for months now, and you’re totally over the wind and cold. I guess we should be glad that we don’t live in Minnesota (sorry, mom and dad). There is one thing you can do to get your hands dirty (literally) and prepare for the 2014 gardening season—do a soil test.

If you've never done it before, it’s a good baseline to start with. If you've gardened for years and keep adding organic matter, fertilizer, cover crops, etc., it will be a great indicator if you need to continue those practices. Soil testing, especially in vegetable gardens, should be as routine as planting peas in the spring. Plus, it’s really easy to do—the soil lab does all the tough work for you.  Follow the steps below to ace the soil test:

1. Gather your tools. In this case, I’m using a soil probe (but you can use a shovel or trowel), a plastic bucket and a container for submitting my soil sample. Some Extension offices may have probes that you can borrow or rent for a small fee. It’s really important that your bucket is clean and made from plastic—metal (especially rusted metal) can interfere with your results. The sample jar I’m using is one the CSU Soil Testing Laboratory provides (available at your local Extension office), but a quart-sized zip-top bag will work, as will paper bags.

2. Scout your area. In this example, I’m taking soil samples from a lawn, but this could be your garden, landscape bed or any other area you wish to test. If you’re having “problem areas” in a lawn or garden, then consider testing that section separately. Yes, you’ll have to pay for two soil tests, but it might be worth it—especially if you've had continual problems growing in that spot.

The lawn can be dormant;
soil may be sampled anytime the ground isn't frozen.

3. You want to get a representative sample from the entire area. You can do this by pulling at least 12-15 samples, which you will mix together. For the lawn, you’re looking for cores about 4” deep (or collect aeration cores and use those—just be sure to remove the thatch and grass).  In the vegetable garden, use a shovel or trowel to sample about 6” deep. Gathering multiple samples, mixing them together and submitting a subsample of the soil collected will be key to a successful soil test.

Gently push down on the probe to 4-6" deep.

Sample of soil pulled from the turf.

Remove the thatch and grass from the soil core.

4. Gather all your samples together in the clean plastic bucket, break up the big clods and then mix well. Remove any large roots or rocks. Fill your sample container with a portion of the mixture and put the rest of the soil back in the garden (or on the lawn).

Chunky cores.

Cores broken up.

Pour your sample into your sampling jar or baggie.

5. Do not send the lab wet soils, so let your sample air-dry for a few days before packaging it up. Then send it off for analysis. A routine soil test at CSU will cost $31 and includes pH, soluble salts (EC), nitrogen, phosphorous, potassium, organic matter, soil texture, iron, sulfates and some micronutrients. Or you can pick and choose what you want to test for. Some gardeners in flooded areas are testing for heavy metals, which is an additional charge. You should get your results via email in 7-10 days.

Let your soil sample air-dry for a couple
days before submitting to the lab.

6. A soil test will not tell you about pesticide residuals, toxic compounds, microbial activity, water requirements, compaction levels or why you cannot grow tomatoes worth a darn.

7. While CSU is a great place to test your soil, there are other private labs that can do the same thing. CSU Extension Fact Sheet #0.520 “Selecting an Analytical Laboratory” lists multiple places for you to consider.

In the next blog, Tony Koski will explain how to interpret and use your soil testing results. Numbers are great, but what do you do with them? And will it lead to your best tomato crop ever?