JoAnne Skelly: Fall lawn fertilization

This spring, I told myself I would remember to fertilize the lawn in the fall because I forgot in 2019. I noticed the grass didn’t seem as strong this year and I had a lot more weeds such as clover and black medic infesting the lawn. Now fall is here and I’m ready to fertilize!

I have purchased two kinds of generic fertilizers, a 16-16-16 and a 21-0-0. The numbers refer to amount of nitrogen – phosphorus – potassium in the product.

I prefer to use a lower nitrogen rate in the fall to slow growth down a bit, but to give the lawn the other two nutrients that will boost root development and food storage in the grass plants. This will make for strong growth in the spring.

However, I have one lawn riddled with black medic, a clover-like annual plant with runners and yellow flowers. The higher nitrogen rate should help strengthen the grass to out-compete the weed seedlings in the spring. By following up in the spring with a high nitrogen fertilizer, I should be able to slow down the black medic infestation without using an herbicide.

I use a fertilizer spreader with wheels for even coverage because I have so much area. It’s too difficult to do efficiently with a handheld spreader. I dump a 20-pound bag of fertilizer in the hopper with the controller set at half the amount recommended on the bag.

Then, I go one direction first, say north-south, and follow up by going east-west. By using this crosshatch pattern, I apply the full amount and avoid streaks where I missed fertilizing some areas and applied too much in others. Too much fertilizer burns the lawn and turns it brown.

Before I fertilize, I water the lawn well. After I fertilize, I water again to wash the fertilizer off the surface of the grass blades and into the soil. Fertilizer left on the surface of the blades can burn the grass.

Sometimes people ask me if they should mow before fertilizing. If the grass is excessively long, that might be a good idea, to allow the chemical pellets to get to the soil instead of sitting on long grass blades.

A strong healthy lawn is the best defense against lawn weeds. I don’t advise using fertilizers with herbicide in them. These products are primarily weed killer rather than fertilizer. In addition, they may damage trees, shrubs and other plants.

JoAnne Skelly is associate professor and Extension educator, Emerita at University of Nevada Cooperative Extension. She can be reached at skellyj@unr.edu.