soil test for organic vegetable gardener

Asked January 21, 2020, 9:46 AM EST

I had my soil tested years ago and received information like: apply ---- lbs of phosphorous per ------acres. Seems helpful for farmers but not organic home gardeners;I do not use chemical fertilizers. Where do I get a test that will give me information I can use? I want to know the ph of my soil, whether it has sufficient organic matter, trace minerals, and how much organic P, K I might need. I hear home kits are not accurate but the professional test was unusable.

Carroll County Maryland

5 Responses

Yes, the soil test results can sometimes be daunting to interpret and adjust to home garden scales. Since it was tested years ago, we'd recommend re-testing. Nowadays at least, if you check-off "vegetable garden" or "garden" on the testing form, results should come back in pounds per hundred or thousand square feet - a much more useful metric. We have a list of area soil testing labs here, in case you wanted to try again, under "how to select and use a soil testing lab": https://extension.umd.edu/hgic/topics/soil-testing
You are welcome to attach an image of the results you received so we can see what was tested, or share the results with us of the new test. Home kits are cruder than soil labs, yes, but they also do not test for all of the elements that the labs do (often just N, P, K, and pH). That said, micronutrient deficiencies are uncommon.

Most Maryland soils have adequate P and K for ornamental garden plants, though cropping plants can be "heavy feeders" and some may require repeated applications from season to season. That said, we want to avoid pollution from over-application of nutrients, and test results will help us learn if you already have sufficient quantities or if they need to be supplemented.

Organic sources of nutrients come in many forms but typically use ingredients such as kelp, fish emulsion, feather, bone, or blood meal, greensand, and more. The list of ingredients on the package will mention sources, and typically manufacturers will either have their product OMRI listed or otherwise label it as organic. Given the popularity of organic gardening, garden centers will often have a whole section of fertilizer options that are organic.

The simplest conversion, while an extra step, would be to convert your garden size to a fraction of an acre. Since there are 43,560 square feet in an acre, this will, of course, shrink the pounds per acre recommended quantity considerably. Fertilizer numbers, which are standardized, are referring to the weight of that nutrient per package. In 10-6-4, as an example, 6 pounds of that package is phosphorus. The amount of fertilizer needed will depend on the kind of fertilizer you need to use.

Most home gardeners find that with yearly addition of organic matter, nutrient supplementation is not needed for healthy plants and a good harvest. If you have grown vegetables in this space before without symptoms of nutrient deficiency, odds are good that your levels are sufficient. Since over-fertilization can lead to various problems (even outside of pollution), it's best to get a handle on the current levels first. Work is currently being done on publications for our website on fertilizer information.

Miri

Thanks Miri, for your very thorough response. All parts of it are much appreciated. Images of my 2011 soil test are below. One confusing thing was that my P was High and my K Very High yet they still recommended 40 lbs/acre P and 60 lbs per acre K. Boxes for trace elements were blank so I have no idea if they were adequate. My Soil ph is 6.8 and Buffer pH is 7.75 (what's the difference?) but there is no indication whether this is fine or if something should be adjusted. What we have done since then is just add compost and leafgro over the years. For all these confusions we have never had the soil tested again. Our goal is simply to grow the healthiest vegetables possible that contain the micronutrients needed. Thanks again for your help.

We are not sure why fertility recommendations were so high. It is possible they were computer generated results. The high phosphorus and potassium levels means you do not have to add more and you do not have to worry about the trace elements. Adding compost is a good practice.

The organic matter is pretty high and no fertilizer is recommended. Your soil pH range is fine. A good pH range for vegetable gardens is 6.2-6.8.
The buffer pH is used to determine the lime rate if needed. Here is a page from our FAQ's on soil testing for more information on this. https://extension.umd.edu/hgic/topics/soil-testing#pH

We recommend that you test your soil now and about every 3-5 years. A basic soil test will give readings for soil pH, phosphate, potassium, magnesium levels and organic matter. You should also test for lead in a vegetable garden. Here is our page on soil testing including a video on how to take a sample, and a list of regional soil testing labs. U of Delaware includes lead in their basic test. https://extension.umd.edu/hgic/topics/soil-testing

Marian


Again, thanks for your prompt and thorough reply!

Marcia