How much fertilizer does my lawn need? What kind should I use? And when should I apply it?
Great questions. Glad you asked! Here in the Houston area our lawns are warm season turf species such as St. Augustine, zoysia and bermudagrass. These turf species benefit from supplemental fertilizing during the growing season to maintain their density. However many residents overfertilize their lawns. This results in nutrients lost to runoff, which can contribute to pollution of our water. Overfertilizing also result in shallow rooted turf that is more prone to damage from pests and less resilient in droughty conditions.
Fertilizer rates and frequency depend on type of turf and its use. For example a bermudagrass sports field with weekly wear and tear will need to be fertilized several times during the growing season, while a home lawn that receives very little foot traffic may only need to be fertilized once or at most twice a year. As a general rule apply ½ to 1 pound of nitrogen per 1,000 square feet of lawn area in the spring after you have mowed the lawn twice (mowing weeds doesn’t count). By that time the lawn will be actively growing and will benefit from the added nutrients. The second time to fertilize is in early October.
A soil test is the best way to determine the actual nutrient needs of your lawn. In the absence of a soil test a good general purpose fertilizer is one that contains a 3-1-2 or 4-1-2 ratio of nutrients. So for example 6-2-4 or 15-5-10 would be examples of fertilizers with a 3-1-2 ratio of nutrients. A simple way to know how much fertilizer to apply is to divide the first number on the bag (nitrogen) into 100 to get the pounds of that fertilizer for 1,000 square feet of lawn.
To avoid streaking, apply half of the fertilizer in one direction and the other half at a 90 degree angle across the lawn. Sweep any fertilizer that landed on the driveway or sidewalks back into the lawn. Then apply ½ inch of irrigation (or rainfall) after application to start to release the nutrients to the growing turf.
One thing to keep in mind is that your clippings are the best fertilizer for your lawn! They contain the right ratios of all nutrients, not just the big three, and decompose rapidly in our warm, humid climate releasing their nutrients to the soil. Over a season of mowing this can add up to a lot of nutrition. Did you know that your lawn mower puts out more nutrients than your fertilizer spreader? So don’t bag your clippings! Recycle them back into the turf. Turf that has the clippings recycled may be fertilized only once per year, or you might even skip a year if the lawn looks fine.
One final comment regards weed and feed combination products. These may not be the best choice for your lawn for several reasons. First, the time to weed is usually not the time to feed. Depending on what herbicide is in the product and whether it is a preemergence or postemergence herbicide, it may not be effective on the weeds you have in your lawn. Finally when overapplied some products can damage trees and shrubs whose roots run under the lawn. The best weed control is a dense, healthy turfgrass so build that over time and your weed problems will be minimized. When you do need to control weeds, have them identified and a proper strategy, product and timing recommended for best results with minimal environmental impact.