Questions from the Master Gardener Hort Line: Soil Testing, How Do You Get One and What Does It Mean?

by Pat Vance

Volunteers for the Philadelphia Master Gardener Hort Line have researched and answered some interesting questions. From time to time, we'd like to share some of those questions with you.

If you have a question about gardening, call us at 215 314 8711 or send an email to philadelphiamg@psu.edu

There are more questions about soil testing than any other topic on the Hort Line. We get questions about how to have testing done as well as how to interpret the results.

Soil Test Kits

Getting a soil test is simple. Stop by any Penn State Extension office to pick up a kit. The address for the Philadelphia office is 675 Sansom Street, Philadelphia, PA and the phone number is (215) 471-2200. Call ahead to make sure someone will be there. The cost for a basic soil fertility test is $10. The kit consists of a sample bag, envelope, and form to be completed for your garden.

You can also print a pdf of the form, collect samples in your own plastic bag, and mail it in your own envelope. This is the ink to instructions on submitting samples:

http://agsci.psu.edu/aasl/submitting-samples

To print the form, go to this url:

http://agsci.psu.edu/aasl/soil-testing/soil-fertility-testing/soil-fertility-submission-forms

Open and print the pdf for “Individual Submission Form for Turf, Home Garden, Noncommercial Fruit, Flower, Woodlot, Christmas Trees and Landscape Plants.”

Include a check payable to “The Pennsylvania State University” along with your sample and completed form.

Complete the entire form as instructed.

Different plants have different nutritional requirements. Read the list on the second page of the form and choose the one that most closely describes your garden. Include the serial number from the bag if using a kit from the office. You can leave that space blank if you are using your own bag.

Any clean garden trowel will work to collect samples. Collect soil from the top 6 to 12 inches from 5 to 10 different spots in the garden to get a good representative sample. Remove plant debris and stones. Dry the soil on clean newspaper and then place it in your sample bag.

Be sure to label the bag with your name! And mail it to the address on the form.

If you have multiple beds, each with a different use, you may want to submit more than one sample, with a completed form and fee for each one.

Test Results

Your report will arrive in about 2 weeks. There will be a text box labeled “Soil Nutrient Levels” that will list pH as well as phosphorous, potassium, magnesium, and calcium levels. Look at the bar graph to see whether those levels are below optimum, optimum or above optimum. The lab will adjust this for your stated garden use. The actual values are listed in a box at the bottom of the page. If any item is not within the optimum range, there will be suggestions in the text box below.

Choosing a Fertilizer

To address nutrient levels, there will be a recommendation for fertilizer. Fertilizers available in garden centers will have an N-P-K value consisting of 3 numbers.  The first number is the total percentage of nitrogen (chemical symbol N), the second for phosphate (chemical formula P205), and the third for potassium (chemical formula K2O), usually in the form of potash.

For example, a fertilizer with an N-P-K value of 5-10-50 would consist of 5% nitrogen, 10% phosphate and 50% potassium. Fertilizers come in a variety of compositions of these chemicals. Typical combinations include: 5-10-50, 5-10-10, 10-10-10, 8-0-24, and 6-6-18. You can see that these fertilizers would give very different results in the garden. Your soil test will help you decide which of these would be best for your garden.

Keep in mind, though, that chemical fertilizers must be applied correctly. Too little will have minimal effect, and too much can harm rather than help. Follow directions on the package carefully.

Also, chemical fertilizers don’t have a long-term effect on the soil. The addition of compost and/or composted manure can make more permanent improvements. You can add bone meal to increase phosphates and kelp to increase potassium. These are available at garden centers. Compost will take longer to improve your soil than chemical fertilizers, so you may want to add fertilizer for a year or two while the compost does it’s magic.

pH Analysis

Another important part of your soil test is the pH analysis. The lists on the back of the submission form shows that plants vary widely in their optimum pH level. pH also affects how well your plants take up nutrients.

pH is a measure from 1 to 14 that indicates acidity or alkalinity. Low pH is acidic and high pH is alkaline or basic. Neutral pH is 7.0, where a substance is neither acid nor basic. pH units change by an order of 10, so a pH measurement of 6.0 is 10 times more acidic than a pH of 7.0.

Generally, vegetable gardens should be about pH 6.5, or a little lower than neutral. But some plants, such as blueberries like to grow in acidic soil, while clematis, for example, thrives in slightly alkaline soil. You will need to do a little research on your plants to be sure you are working toward the correct pH.

As with nutrients, there are actions you can take to change pH. Your soil report will recommend an amount of lime to increase the pH of your garden. The addition of sulfur will decrease pH but this has the same short-term effect as chemical fertilizers. Compost and other organic matter will decrease the pH of soil more gradually, but will be a more long-term fix.

More Information

For more information on building healthy soil, go to these links:

https://extension.psu.edu/gardening-from-the-ground-up

http://agsci.psu.edu/aasl/soil-testing

http://agsci.psu.edu/aasl/soil-testing/soil-fertility-testing/handbooks

If you have any other questions and are not sure where to turn, ask the Hort Line! If we don't know the answer, we know someone who does!

Annual Garden Day and Plant Sale Announcement

The Annual garden day is once again being held at the Horticulture Center in Fairmount Park.

The entrance is off Montgomery Drive near Belmont Plateau. Upon entering the park follow the road

around and behind the center. 

At this years event there will be testing of soil for lead and a speaker on soil health and testing.

Directions for sample taking is below.

Why Do Soil Testing?

A recent article in Fine Gardening Magazine explained why we gardeners should do soil testing. Here is the article and also the information for obtaining a soil test kit from Penn State Extension in Philadelphia.
The soil will be sent to the Penn State Lab and a report sent back to you.

To get a soil test kit from the extension go to http://extension.psu.edu/philadelphia/programs/master-gardener and look under the Hort Line tab on the left.

A video on how to do your sample:

http://www.youtube.com/watch?v=qCbO5a5JZpk&feature=youtu.be

Soil Testing is Worth the Effort

by Lee Reich     from Fine Gardening
There’s no such thing as a free lunch, even in the garden. Depending on your soil’s native fertility and what you grow, your plants might perform for years without needing additional fertilizer. But sooner or later, the free lunch ends. Hungry plants won’t squeal like starving pigs, but they eventually will show their unhappiness by displaying stunted growth and, depending on the particular nutrients they lack, off-color leaves. A periodic soil test lets you catch nutrient deficiencies before they progress that far. Besides indicating nutrient deficiencies, a soil test can also provide information on soil acidity, the percentage of organic matter in your soil, and your soil’s texture. But it will not tell you anything about poor soil drainage, insufficient sunlight, or insects and diseases. These threats to plants also can cause off-color leaves and stunted growth, so rule them out first before moving on to a soil test.

Know what to test for

Whether you’re testing the soil at home or sending it to a laboratory, you’ll have to decide what to test for. At the very least, test your soil’s pH, which is a measure of how acidic your soil is. If the pH level isn’t in the correct range, plants cannot take up nutrients in the soil. You should also test for phosphorus and potassium because plants require both of these nutrients in relatively large amounts. A complete checkup would include tests for nutrients that are essential but needed only in minute quantities, such as iron, manganese, and zinc. If you regularly enrich your soil with an abundance of compost and other organic materials, micronutrient problems are unlikely.
Some laboratories are also set up to test soils for toxic elements. For example, if your house is more than 50 years old, you might want to test the soil for lead from lead-based paint that has flaked or was scraped off the siding. On former farm sites, you might want to test for DDT or arsenic. Although neither is approved for home agricultural use, both are persistent pesticides that were widely used in the past.

A proper sample is critical

Proper sampling technique is an important part of soil testing. Even in a modest-size garden of 1,000 square feet, 1 cup of soil—the amount typically used for a test—represents only about one one-thousandth of one percent of the top 6 inches of ground. So that 1-cup sample had better be representative of the whole area.
To get a truly representative sample, dig in a few random spots around the test area and mix the soils together. Avoid sampling any anomalous spots such as near a fence or where you fill your fertilizer spreader or once had a compost pile. If the test area itself seems insufficiently uniform because of, say, a large, wet, sunken portion, then divide the area into two or more separate test areas. Areas devoted to different kinds of plants, such as vegetables and lawn, require separate samples. Vegetable and flower gardens, though, may be sampled together.
Collect soil to a depth of 6 inches, which is approximately the depth of most plants’ feeder roots. Before you dig, remove any surface debris such as wood chips, compost, plant residues, or sod, then make a hole to the required depth. Discard the first shovelful of soil. It’s a cone-shaped slice, so it contains a greater proportion of soil from the surface than from lower down. Take another slice, uniformly thick from top to bottom along the edge of the hole you just made.
Throughout your sample preparation, avoid contamination from dirty hands or utensils. Gather together samples from each test area into a clean, plastic bucket, then mix and crumble them, discarding stones, sticks, insects, and other debris as you mix. Spread the soil on a clean baking pan to air-dry for a day, then remove about a cup for testing.
If you are sending your samples to a lab for testing, you will get a recommendation for fertilizer and for amounts of lime or sulfur needed to adjust the pH level. Fertilizer recommendations are based on what is in the soil and the kinds of plants you intend to grow. Follow these guidelines closely because too much of any nutrient can be as harmful as too little, causing nutrient imbalances, even death, to plants.

Nitrogen skips the soil test

Soil tests rarely determine nitrogen levels, even though this is the nutrient for which plants are hungriest. Nitrogen is readily lost from soil, puffing away as a gas or leaching from rainfall beyond the reach of roots. The stuff is simply too evanescent to make testing for it meaningful at any single point in time.
Most soil nitrogen is locked up in organic matter, so determining the percentage of organic matter in your soil offers an idea of the amount of nitrogen potentially available. I say “potentially” because nitrogen becomes available as soil microbes chew away at organic matter; the amount that plants actually get waxes and wanes as weather conditions influence microbial growth. If your soil contains about 4 percent organic matter, you probably have an acceptable level of nitrogen.