More and more Bay Weekly readers are having their soil tested, as evident by the number of soil test results that I am receiving by e-mail. In nearly all I have reviewed during the past year, soils are much too acid, and lawns have a surplus of phosphorus (P) but are deficient in sulfur (S) and boron (B). Very few results indicate near neutral or alkaline soils, except in azalea beds where hardwood bark mulch has been repeatedly applied.
What this means is that many gardeners are wasting money applying fertilizers and not achieving desired results. They are also contributing to the nutrient pollution of the Bay by applying excessive amounts of certain fertilizers.
If your soil is excessively high in P and low in S or B, you are wasting money applying fertilizers. If your soils contain optimum or high levels of P and you are applying a lawn fertilizer containing P, you are not only breaking the law but also creating trace element deficiency problems. Excess levels of P in the soil cause fixation of essential trace elements such as iron (Fe), Zinc (Zn) and copper (Cu).
In consequence, you have a pale green lawn instead of a dark green lawn.
A deficiency of S in the soil reduces a plant’s ability to synthesize proteins and amino acids. If you are growing vegetables and fruit in soils deficient in S, your harvest will not have the same nutritional content as those grown with adequate levels of S.
Sulfur deficiency was never a problem when we were breathing polluted air. Because of strict EPA air-quality regulations your lawns and gardens are no longer receiving free sulfur every time it rains. Most commercial fertilizers do not contain adequate levels of S to correct deficiencies. You must apply wetable sulfur, flours of S or granulated S, as well as regular fertilizer.
Boron is another essential element becoming deficient in many soils. Boron is responsible for the translocation of the sugars and other metabolites manufactured by photosynthesis in the leaves to the roots. The B problem is most severe in sandy soil but is becoming more common in heavier soils. To solve this problem, I recommend applying Borax. The amount must be calculated on the amount present in the soil and the type of soil being treated. It is easy to apply an excessive amount, which can damage or kill plants.
To have your soil tested for B, S, Cu, Fe and Zn, you must specify the desired test on the information form when submitting samples. If you have never had the soil tested, I highly recommend a complete analysis. However, if you have your soil tested every three or four years, the cheaper pH, organic matter, phosphorus, potassium, calcium and magnesium test is adequate. If the soil is a sandy loam or a loamy sand, a complete analysis is highly recommended every 10 years because most likely B and S reserves will have been deleted.
You can best understand the importance of good plant nutrition by visualizing a water barrel. If the barrel has a hole, it can only be filled to the height of the hole. In other words, the barrel cannot retain all of the water it was designed to hold. With plants, maximum growth cannot be achieved unless all of the nutrients are available to the roots. Excess phosphorus or pH either excessive or low will deny certain nutrients to the roots.
Reading Soil Test Results
Q I finally obtained a soil test per your recommendation and am sending you the results. I raise vegetables on only 200 square feet and am looking for your suggestions on any amounts of Bloom, compost or any other matters.
–Doug Corner, by email
Your soil should also be tested for sulfur, boron, zinc, copper and iron. The soil lab most likely still has samples of your soil. Contact them and have additional tests suggested. The problem I see most often in soils like yours are a deficiency of sulfur and boron.