by Doc Stalker, El Paso Master Gardener
Credit: First Leaf of Autumn by Eric Sonstroem (CC BY-NC 2.0)
Summer’s temperatures are finally starting to drop, and the school zone caution lights are flashing again throughout El Paso County. That means the deadline for the most important fertilizer application of the year is right around the corner.
A final application of fertilizer each fall helps warm season grasses store up extra energy before going dormant over the winter months. That stored energy is critical for lawns to ‘green up’ next spring as soon as the weather is warm again. It’s important to give enough time for the fertilizer to work before the grass dormancy period starts which in El Paso is usually around mid-November and depends on when the fall temperatures fall into the frost range. So, don’t risk applying any fertilizer to your lawns after early October.
Hopefully you have a recent soil test analysis to tell you the exact amounts of the nutrients (nitrogen, phosphorus, potassium, etc.) your lawn needs throughout this year. No? Well then, applying a recommended maximum of just ½ pound of a soluble nitrogen fertilizer, like ammonium sulfate (21-0-0), per 1,000 ft2 of lawn is all that’s needed to get your lawn ready for next spring.
Without going into the chemistry, in addition to nitrogen, ammonium sulfate also contains 24% sulfur, which will help to lower the pH level of El Paso’s alkaline soils a bit. That’s definitely an added bonus to help keep your lawn healthy.
The number “twenty-one” in 21-0-0 indicates the contents of a bag of ammonium sulfate are 21% nitrogen. By doing some basic math, or consulting an online turf fertilizer calculator, you’ll discover only 2.4 pounds of 21-0-0 fertilizer is required to spread ½ pound of nitrogen over 1,000 ft2. However, applying too much fertilizer can damage lawns. So don’t be thinking, “If that recommended half-pound of soluble nitrogen is good, a whole pound will be twice as good.” It just doesn’t work that way with fertilizers or research-based recommendations.
Knowing the size of your lawn and the right amount and type of fertilizer needed can eliminate doubts about which bag of fertilizer to purchase at a garden center and will probably save you some hard-earned bucks, too. So measure your lawn, borrow the kitchen scale, and weigh out and apply the correct amount of 21-0-0 fertilizer before that early October 1st deadline. And, be sure to thoroughly water-in the soluble fertilizer into the soil immediately after it is applied.