11/6/2012 - By Marshall Horsman

We have all seen it. Plants just kind of "sitting there", color pale and a lack of luster. At first guess, one might say the plants are "running out of gas" or are nitrogen deficient. But they were fertilized, not too long ago. Hmmmm. What you may be seeing is sulfur deficiency. Or as our friends in the United Kingdom would say, "sulphur deficiency". You guessed it. This month’s nutrient of the month is dedicated to our last secondary nutrient, sulfur.

Sulfur plays several roles such as being a major component of proteins, amino acid and enzymes, aiding in chlorophyll formation as a catalyst, helping in root formation and seed development. In agriculture, elemental sulfur will lower pH levels and help minor element availability, in particular iron and manganese. But as it is soluble and leachable, it is not a permanent solution, especially in sandy or high alkaline soils.

Sulfur is available to plants in a sulfate form, often as sulfate of potash, sulpomag, magnesium sulfate (Epsom salts), or ammonium sulfate. Even minors in a sulfate form contribute to sulfur fertility, however there are situations where fertility programs do not offer enough sulfur. Examples of sulfur deficient practices include greenhouse growers who solely use liquid feed, or those on premium NPK fertilizers that have nitrogen and potassium in the nitrate form only.

For years, nutricote programs left soil analysis readings low in sulfur and magnesium. Later, coated magnesium sulfate was added in some blends to compensate for this but as coatings are controlled release, levels are often inadequate.

Harrell’s fertilizer soil and tissue readings are typically better in sulfur and magnesium levels. A blended mix including some coated potassium sulfate and even some upfront more soluble sulfate is the best of both worlds. This is especially true in woody ornamentals, which do have a higher demand on sulfur than say some " foliage" crops. Be careful, because too much sulfate in the soil can lead to high soluble salt levels and create a "salt" burn.1

Those anemic plants, low in sulfur, can actually get corrected quite easily with a few epsom salt sprays at 1.5-2.0 lbs per 100 gallons of water. This is not just for magnesium anymore - yes, sulfur, the 10th most abundant element in the universe, holding at 16 on the atomic number chart. There are a multitude of reasons it is helpful for plants: elemental sulfur as a dust on vegetables as a biological fungicide and miticide; inside plants, for helping make chlorophyll; a pH adjuster as a soil additive; or if you want to assure good sulfur levels in plants, simply use Harrell's.

By Marshall Horsman, Technical Services Manager, Harrell’s LLC