Keep it Green, by Michael Womack
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Saturday, September 1, 2001

Lush lawns need nitrogen fertilizers

We are still under water restrictions in Corpus Christi and need to manage not just our lawn watering, but also fertilization accordingly. Frequent applications of nitrogen fertilizers promote fast, healthy grass growth - which in turn increases its water requirement. Reduce your fertilizer application frequency to slow down turf growth and make it more water efficient.
   Don't misunderstand, proper lawn fertilization in fall is particularly important for a thick, healthy lawn next spring. It also reduces risk of cool season turf fungal diseases like take-all root rot.
   But pushing your grass with a lot of fertilizer now may not be the best management practice with our current water considerations.
   Timing of fertilizer application is important. Fall fertilizer applications are typically applied sometime between mid September and early November, depending on the weather. A cooler fall requires an earlier application within that time frame. Late application of nitrogen fertilizers will promote late-season growth and make your grass and perennials more susceptible to freeze damage
   Most of our lawns are warm season grass varieties which grow little above ground during the winter, but the root system continues to develop even with reduced top growth. Fall fertilization promotes good root growth and over-wintering of your grass.
   When buying fertilizer, read the label. Every bag of fertilizer has three percentage numbers that correspond to nitrogen (N), phosphorus (P2O5) and potassium (K2O), and commonly called potash. For example, a 20-10-20 fertilizer con
   tains 20 percent nitrogen, 10 percent phosphorus and 20 percent potash. A 30-15-30 fertilizer has the same nutrient ratio but with less filler.
   Fertilizers also may include sulfur, calcium or magnesium. Micro-nutrients such as iron, zinc, manganese or molybdenum may also be in the fertilizer.
   Don't assume that you are getting any of these micro-nutrients even if the fertilizer is labeled as a 'complete' fertilizer. 'Complete' only refers to the presence of nitrogen, phosphorus and potassium.
   Two important points to remember are:
  

Keep phosphorus (middle number) levels as low as possible; and
  

Use slow-release nitrogen, if possible.
   Soil samples in our area often show an abundance of phosphorus, especially in the heavy clay soils. You don't want to add more phosphorous because excessive levels can tie up micro-nutrients such as iron and zinc in the soil, making them unavailable to your grass.
   Slow-release nitrogen is recommended for fall fertilizer applications because it provides some fertilizer to the grass over a longer period of time, up to three to four months depending on temperature and rainfall.
   Slow release fertilizers also prevent excessive nitrate runoff during this period with traditionally more rainfall than summer months.
   That provides some protection to our bays and estuary system.
   To prevent green stripes caused by application overlap, applying half the fertilizer at first in one direction (for instance east to west); then go back and apply the other half perpendicular to the first application (that is, north to south).
   Remember that you need to water in the fertilizer immediately after application. It is important to wash the fertilizer off of the grass blades to prevent burning. Apply about ½ to ¾ inches of water to wash the fertilizer into the soil.
  
  

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Michael Womack is a horticulturist with the Texas Agricultural Extension Service. Got a question? Michael Womack will answer landscape and gardening questions. Call 886-4648, category 3025 to record your question. Write Keep It Green, Corpus Christi Caller-Times, P.O. Box 9136, Corpus Christi, TX 78469 or email wm-womack@tamu.edu

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