Yellow/Lime Colored St. Augustine Grass - Knowledgebase Question

San Antonio, TX
Question by alegraison
June 27, 1999
I have an established St.Augustine lawn shaded by very large oak trees. The lawn is thick and grows quickly but has several variations in color from yellow to very dark green. I use quality fertilizers and and still have the problem. I have used ironite with very little improvement.

Answer from NGA
June 27, 1999


The problem is iron chlorosis due to your high pH soils. Other contributing factors include high phosphorus levels (the middle number on a fertilizer bag), and cool and/or wet soil conditions.

Fertilize you turf with 21-0-0, an acidifying fertilizer at a rate of 5 pounds per 1,000 square feet in mid-April and June. Then in mid-October, use a product similar to 15-5-10 at a rate of 7 pounds per 1,000 square feet. Return your clippings to the turf by mowing with a mulching mower. Water only every 5-7 days applying 1/2 to 1 inch of water when you do. A coffee can or rain gauge can be used to determine how long it takes to apply this amount.

Chelated iron products can be used as a quick fix to the iron deficiency. Applying a pound of wettable sulfur per 100 square feet through a hose end sprayer is another good idea to help in the longer term. This should be done in early spring and again in late fall when temperatures are cooler.

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