Gardening: Testing can determine soil’s nutrient needs

The past couple of weeks I’ve written about bulk materials to improve your soil. This week I want to tell you about the macro- and microcomponents or nutrients that might need to be added to your soil.

Macro nutrients are the nitrogen (N), phosphorus (P) and potassium (K) found in fertilizers and represented as NPK. NPK is shown as the three numbers (10-10-10 as an example) found on the fertilizer bag and represent the percentage of each element in the fertilizer mix. Nitrogen helps with photosynthesis and plant growth. Phosphorus stimulates root development, enhances energy transfer and promotes fruit development. Potassium regulates water usage, improves disease resistance and enhances crop quality. Often the NPK in organic fertilizers is released more slowly than those in conventional fertilizers that release their nutrients quickly. In general, slowly released nutrients help grow stronger and more resilient plants.

Micro soil nutrients include iron, lime, super phosphate, aluminum sulfate and iron sulfate. They are very small components of the soil that change or enhance the activity of the macronutrients. Lime raises the soil pH, aluminum sulfate lowers the pH which helps acid-loving plants like rhododendrons, hydrangeas and blueberries while iron improves plant growth and helps release other nutrients to the plants.

But how do you know which macro- and micronutrients and how much of each you need to add to your soil? Do you need any of them at all?

This isn’t a time for guessing. The only way to know what you need is to do a soil test that measures the macro- and micronutrients as well as the organic content and the pH of the soil.

The best soil tests are those run through a soil testing laboratory. You can buy kits at the garden center, but they often only give you broad ballpark readings. This may be fine if that’s all you want but if you are building productive soil, you will want more accurate readings.

There are lots of labs listed on the internet, but their test methods can be very different. Locally, there are two labs in Moses Lake, Soiltest Farm Consultants and Best-Test Analytical Services that provide homeowner testing. Tests run between $40 and $60 depending on the type of test you ask for.

Follow the directions from the soil test lab on how to take the sample, package and ship it. In general, start with a very clean shovel and plastic bucket to reduce possible contamination. Remove sod or surface debris and then take a 12-inch-deep slice of soil. Take the middle inch from the shovel and place it in the bucket. Take multiple samples across the area. Thoroughly mix the samples together in the bucket and then draw out two cups of soil and place them in a closeable plastic bag. Fill out the form and mail it to the lab. The report you get back will give you recommendations on what to add and how much, if anything, to your soil.