Sunday, June 7, 2020 By: Ask A Master Gardener

Soil Tests Help Select a Fertilizer



Tom Ingram: Ask a Master Gardener
Sunday, June 7, 2020
Q: With all the different fertilizers out there, how do I know which one I should be using? AR
A: Fertilizers can be confusing. They come in a variety of strengths with a variety of numbers and for the beginner or novice, it can be overwhelming. So let’s break it down.
The fertilizers you find at the store have a series of numbers on the bag. These numbers can be something like the following: 10-20-10, 19-19-19, 3-17-17, 31-0-4, 46-0-0, etc. Those numbers coincide with the percentage of nitrogen, phosphorus, and potassium in each particular product. So, if a product says it is 10-20-10, that means it contains 10% nitrogen, 20% phosphorus and 10% potassium. If it says 46-0-0, that means that it contains 46% nitrogen, 0% phosphorus and 0% potassium.
So how do you know which one you should use?
The best way to know for sure is to have your soil tested. This may sound a little intimidating, but it is a simple process.
First, you will need to collect the soil sample. You can collect this sample using a specialized soil sampling tool or just use a garden trowel. A bulb planter works well also. The trick is to get between 15-20 samples from the area you want tested. These samples need to contain soil to a depth of 6 inches. If this is your yard, get 15-20 samples from various points in your yard, put them in a bucket, mix it up, remove the twigs and fill something about the size of a sandwich bag from the soil in your bucket. If you are wanting a soil test for your vegetable garden or your flower bed, get your 15-20 samples from those areas.
Once you get your soil sample in a bag, bring it to the OSU Extension office, 4116 E. 15th St. Even though the office is closed, there is a black mailbox on the south side of the building (in the back) where you can fill out a form and leave your sample. There is a $10 charge for a soil test. We will pick it up and forward it to OSU, where they will test for pH, nitrogen, phosphorus and potassium. Once tested, you will get a recommendation on what nutrients are needed for your situation. These recommendations will vary depending on what area you are sampling and what you are growing.
Once you have the results of your soil test, you will know how much of each nutrient you need to add to your soil for best results.
So back to the fertilizer. Let us say the test revealed your soil only needed nitrogen, and it was recommended that you add 1 pound of nitrogen for every 1,000 square feet. In this case, you could purchase some 46-0-0 fertilized because it is 46% nitrogen and does not contain phosphorus or potassium. This means that if each pound of fertilizer is 46% nitrogen, you would need about 2 pounds of fertilizer to give you 1 pound of nitrogen. If you purchased 10-20-10, you would need 10 pounds of this fertilizer to give you the 1 pound of nitrogen. Plus (in this case) you would be purchasing phosphorus and potassium that you didn’t need and which might also be harmful to your growing environment.
Yes, you may need to use a calculator, but odds are that getting a soil test will not only be good for your soil but also will ultimately help you save money by not having to purchase nutrients you don’t need.
Garden tips

•Do not work soil if it is too wet. Tilling it while wet will cause damage to the structure and it will take a long time to recover.
•Thatch is a layer of dead and living stems, shoots and roots which pile up on top of the soil at the base of lawn grasses. If it is over ½ thick it should be removed with either a core-aerator or power-rake. Now is the time to de-thatch Bermuda and zoysia. De-thatch fescue, if needed, in the fall.


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